Photo Enlargements And Canvas Prints Glossary
- Acid Free - ( sometimes referred to as "pH neutral") Refers to the fact that a material or substance is not acidic in its composition. The level of acidity is measured using the pH scale, which ranges from 0 to 14. Note that this scale is non-discrete, which means it can take on fractional or decimal values such as 1.5, 4/5 or 6.75 rather than just whole numbers such as 6. A material or substance with a pH value of 7 or slightly more is generally considered to be "pH neutral" and can also be referred to as "acid-free" . A material or substance with a pH value clearly greater than 7 can be referred to as "acid-free" but not "pH neutral". In relation to printing, acidity ( pH less than 7 ) causes paper to decay over time. The first symptom of this is a yellowing of the paper, which will detrimentally change the colour balance of the image. More seriously, the yellowing is part of a chemical reaction that will eventually result in the paper becoming brittle. The speed of this decay will largely depend on the level of acidity initially present in the paper and exposure to other acidic chemicals or gasses over time (also see lignin).
- Aperture - ( or "lens aperture") In photography parlance, refers to one of the key factors that affect exposure. The aperture is controlled by the diaphragm, which is a mechanism built into the lens itself. The diaphragm consists of several overlapping blades which form an opening through which light passes. It is typically located towards that part of the lens which attaches to the camera body. The diaphragm should not be confused with the shutter, which is usually located within the camera's body. The lens aperture is measured in f-stops, which is a ratio calculated by dividing the focal length of the lens (e.g. 50mm) by the diameter of the diaphragm. Some common f-stop values are: f/1.4, f/2, f/2.8, f4, f5.6, f8, f11, f16, and f/22. The smaller the f-stop value, the larger the aperture, and in turn, the greater the amount of light that reaches the sensor / film (assuming that the other exposure factors remain the same). Going from left-to-right, each f-stop value reduces the amount of light by 50% compared to the previous value. (see exposure, shutter)
- Artefacts - In relation to a digital image, describes "unnatural" distortions that are introduced into an image due to some form of over processing. There are a number of different types of image artefacts. File compression artefacts (such as JPEG artefacts) are caused by too much compression being applied when saving a file. An image affected by JPEG compression artefacts will appear to consist of fuzzy squares. Halo artefacts can be caused by over-sharpening (see Print Sharpness), and usually manifest as a pale-coloured "glow" affecting edges or lines. Other forms of artefacts can be caused by the incorrect "handling" of light (see chromatic aberration)
[JPEG artefacts example] [oversharpening example]
- Aspect Ratio - In relation to an image or print, refers to the ratio of the width divided by the height. Put another way, the aspect ratio provides a description of the proportions of an image or print. Most compact digital cameras record photos with an aspect ratio of 4:3. In contrast, most dSLR cameras record photos with an aspect ratio of 3:2.
- Bokeh - (derived from Japanese word "boke", meaning 'blur') - In photography, refers to the creative use of lens blur as a composition technique. The aim of bokeh is to deliberately blur the background or foreground (or both) in order to draw the viewer's attention to a particular area of the photo. One method of achieving Bokeh involves using a lens with a wide aperture setting, which in turn produces a narrow depth-of-field. It should be noted that some lenses tend to be more suited than others for achieving such an effect. Central to achieving effective bokeh is an understanding of the concept of depth-of-field (dof).
[bokeh example]
- Buffering Agent - A substance added to paper during the manufacturing stage to increase the paper's pH value (refer to "acid free" definition) to 8 or higher. This is done to help prevent the paper from becoming acidic over time as a result of the absorption of acidic chemicals or gasses present in the environment (i.e. from the air or from contact with other material). The buffering agent has the effect of neutralising any acidic chemicals or gasses. The preferred buffering agent of archivists is calcium carbonate.
- Bulb Mode - In relation to a camera's shutter operation, refers to a mode that causes the shutter to remain open when the shutter button is pressed, and then to close only when the shutter button is released. Bulb mode can be used to create interesting compositional effects, or to facilitate high-speed photography when used in combination with a high-speed-capable flash (i.e. capable of a very short flash duration, e.g. 1/20,000s). Most modern cameras have bulb mode capability. (see shutter)
- Canvas - In the arts/photographic industries, refers to a heavy, woven material used for printing or painting on. High-grade canvas is derived from either 100% cotton or a combination of cotton and synthetic fibres; is acid-free and optical-brightener-free (OBA-free), and tends to be quite heavy (300 GSM or more) and capable of accepting a large amount of ink (which results in a better dmax, which in turn supports a broader colour gamut, with deeper blacks, better contrast etc). Lower-grade canvas tends to be lighter in weight. It may or may not be acid-free or optical-brightener-free, and is typically not able to accept the same amount of ink as a premium canvas. Relative to other types of paper, canvas tends to have quite a pronounced texture and noticeable weave. Certain types of photos or images are more suited to printing on canvas than others. In general, if it is important to show the very finest of detail in your print, it may be better to choose a smoother class of paper.
- Canvas Prints - Refers to artistic or photographic prints, typically produced using inkjet printing technology. (also see canvas and canvas stretching)
- Canvas Stretching - Describes a popular method used to present canvas. Essentially, it involves wrapping a canvas print over a square wooden frame. Although there is often a small amount of ‘stretching’ involved, this is quite minimal in order to avoid distorting or damaging the print. A better, albeit awkward, description might be "tightly wrapping canvas over a wooden frame". Canvas stretching can be quite labor intensive, sometimes more labor intensive than conventional framing. The techniques and, to a larger extent, the materials used to prepare a canvas frame can vary. For instance, different types of wood with differing strength, weight or shape can be utilised, and different types of fasteners can be used to attach the canvas to the frame. It is important to note that some inkjet canvas is not suited to stretching over a frame as it can be prone to cracking. (also see stretcher bar, gallery wrap, museum wrap)
- Chromatic Aberration - The term 'chroma' refers to colour. The term 'aberration' refers to some sort of unexpected variation. In relation to photography, chromatic aberration describes an undesirable side effect resulting when a camera lens cannot focus the different wavelengths making up light within the same focal plane. Chromatic aberration is evidenced when blurred (or "foggy") colour fringes appear along some of the edges of objects. It is a problem that more often occurs with the cheaper variety of telephoto lenses.
[chromatic aberration example] (see focal point)
- Coating - Refers to a liquid substance that is applied to a print, typically by brushing or spraying, in order to provide additional protection against the fading effect of light and airborne contaminants, and against scratching or scuff marks. Note that the process of coating differs from laminating in that the latter involves encasing the print in a plastic-like wallet using a combination of heat and pressure. The main advantages of coating are: 1) it is more forgiving, and can be applied to a wider range of papers, and 2) It tends to be significantly less prone to yellowing over time. The main disadvantage of coating is that it tends to be more labor intensive to apply.
- Colour Cast - (both subjective and objective measurement) In relation to a photo, describes a situation (not necessarily undesirable, especially in relation to warm colour casts) whereby the overall colour of the photo is affected by the tinge of another colour. Sometimes, a colour cast can be quite noticeable: for instance an old faded photo may show a clear yellow cast as a result of physical deterioration. On other occasions, the colour cast can be quite subtle and can only properly be identified using the features of certain image editors. One of the best ways to minimise the chance of an undesirable colour cast affecting your photo (or reduce the impact of the colour cast) is to manually select the most appropriate white balance setting prior to taking the photograph. More advanced techniques involve the use of tools such as external light meters and grey cards (or colour targets) to determine the most appropriate camera settings.
[colour cast example]
- Collage - Derived from the French word for "gluing". It originally referred to the physical process of gluing a number of pictures, photos or drawings onto a flat piece of paper, in order to create an artistic composition. In terms of digital photography, it refers to the process of compiling a number of smaller digital images into one large digital image, (usually) to create an interesting effect. In addition to photos, the digital collage may contain a number of other elements, such as vector shapes or text.
[digital collage example]
- Colour Proof - It may refer to a reference print that a client supplies to a photo processing centre, along with the corresponding digital image, so that the photo processing centre can reproduce the digital image with colours that are representative of the reference print. Alternatively, it may refer to a reference print (usually smaller in size than the final "real" print) that the photo processing centre supplies to the client in order to assess whether the client would be satisfied with the colours of the final print.
- Colour Quality Control - The processes employed by Giantprint Pty Ltd, both standards-based and proprietary-based, in order to control colour accuracy and colour consistency.
- Crop - In relation to digital image editing, refers to the process of "cutting away" or discarding unwanted parts of an image. Typically, cropping is performed within an image editing program, whereby a square-shaped marquee (i.e. selection area) is placed over the part of the image that is to be retained. Upon clicking or pressing some button within the program, the unwanted parts of the image (i.e. those that fall outside the square marquee) are discarded. Cropping may be performed in an attempt to improve the composition of an image, for instance to remove a distracting object or person. Alternatively, some cropping may be required in order to print an image with an aspect ratio that differs from that of the final print dimensions. This is because, due to the different aspect ratios, the image may not fit within the allocated print dimensions. If, despite the different aspect ratios, the image must not be cropped prior to printing, some form of overall image resize will be required - for instance the image as a whole may need to be reduced in size by 15%. (see aspect ratio)
- Custom Colour Profile - A measurement taken to determine the colour reproduction characteristics of a specific printer, ink and paper combination (note that by "specific", we mean a specific physical instance in use somewhere). By using a profile that is custom-made rather than a generic (i.e. "canned") profile supplied by the manufacturer, the profile will more accurately represent the prevailing colour reproduction characteristics. This, in turn, will help to produce a print that is a closer match to a colour proof. Furthermore, the custom profile will typically allow access to a larger colour gamut than if the generic profile was used.
- Delta-E - (in relation to printed output) An objective measurement used to determine the colour accuracy of a print when compared to some reference print (see colour proof). The lower the delta-E, the lower the difference in colour variation between two prints. Many professionals consider a delta-E result in the range of 3 to 6 to indicate a good colour match.
- Digital Photo Enlargements / Photo Enlargement - Commonly refers to the processes involved in making a digital photograph larger. It may refer to the process of increasing the size of the digital file (for example, a .jpg or .tiff file), increasing the size of the physical print which was derived from the digital file, or both. It is generally accepted that enlarging a photograph from a digital image is considerably more difficult than enlarging a photograph from an analogue (i.e. film/negative based) photograph. This is due to the fact that a digital image has only limited "information" available from which to derive a print. In order to produce a physical print with sufficient resolution and sharpness, special mathematical algorithms may need to be applied to the original digital file. The technique required to enlarge a digital photo will, to a large extent, depend on the size of the original file, the quality of the original photo, and the final print size desired. Poster size photos can be particularly difficult to achieve, and often require the expertise of a professional photo enlargements service in order to produce sufficient resolution and sharpness and thus achieve acceptable results. It should be noted that the techniques used to enlarge a digital photograph can vary quite widely from one processing centre to another.
- Dmax - (in relation to inkjet paper) Typically used as a measurement of the potential maximum optical density of black that can be achieved with a particular paper and ink combination. Optical density refers to the extent to which an ink and paper combination absorbs visible light. The greater the amount of light that can be absorbed, the darker the shade of black that is capable of being reproduced. Therefore, an 'informal' way of defining Dmax is that it represents the darkest potential shade of black that can be achieved. Dmax will fall somewhere within the Density Scale, which ranges from 0.0 to 5.0 (5.0 denotes highest optical density). It should be remembered that, in practice, a Dmax of 5.0 is unachievable. Dmax is commonly used as one of the important indicators of the colour gamut, or range of colours (or the range of brightness/tonal values, in the case of black and white printing) that the paper is capable of reproducing, assuming that the type of ink used remains constant. Another important indicator is the paper's "white point". Some examples: A typical high-end canvas print made with premium pigment ink recorded a Dmax of 1.71. A high-end glossy print, made with the same premium pigment ink, recorded a Dmax of 2.15.
- Dot Gain - (in relation to inkjet/dot-matrix/press based printing) Refers to the tendency for the individual printed dots, making up an image, to physically expand after they have been laid down onto the media and before they have dried completely (to be more precise, we are referring here to mechanical dot gain rather than visual dot gain). Left "unchecked" or unaccounted for, dot gain can have a significant negative effect on the tone as well as the sharpness of the printed image. Dot gain is affected by such factors as: the media used, including the nature of its coating; the ink chemistry; the air temperature, as well as the nature of the printing equipment used. Although the ideal scenario would be for no dot gain to be present, this is virtually impossible. The aim for a given scenario, then, is to (i) minimize dot gain, and (ii) characterize and predict its extent and effects using such processes as linearization and profiling, and (iii) compensate for these effects through software.
- dSLR Camera - An abbreviation of the term "digital single lens reflex camera". A camera that has a viewfinder through which the user views the actual image that is being projected through the lens. Essentially the same as a film-based SLR camera, except that a digital sensor replaces the film. dSLR cameras typically have more manual features and are priced above all-digital compact cameras. Prices vary from approximately $900 AUD to in excess of $60,000 AUD for a top-of-the range medium format Hasselblad dSLR.
- Exposure - Refers to the total amount of light reaching a camera's sensor or film when a particular photo is taken. Other than the prevailing light conditions, there are several key camera settings that determine the exposure. These are: lens aperture, shutter speed, ISO sensitivity, metering mode and the exposure compensation setting, if activated. (see shutter, metering)
- Exposure Compensation - In relation to a dSLR camera's metering system (i.e. not just the light meter, but also the firmware etc involved in making exposure calculations) or the metering system in a digital light meter, refers to an override feature which allows the user to fine-tune the automatically calculated exposure value (EV) based on the need to correct exposure in situations where the prevailing light conditions will fool the system, based on the requirement to expose for a particular area within the scene, or based on some creative aim. The metering system in most modern dSLR cameras performs its EV calculations with the assumption that the total amount of light reflected back from the subject/scene is in the range of approximately 12 to 18 percent reflectance (confusingly called 'middle gray', even though, in this scenario, we are referring to the luminance/"brightness" of the light rather than the colour/saturation of the reflected light). When the total actual light reflecting off a subject/scene is outside this range, the automatic EV calculation will be inconsistent with the prevailing light conditions, and will therefore result in darker-than-expected or lighter-than-expected results. Typically, the exposure compensation value will be a number in the range of -2 to +2. Each 1 EV value change corresponds to an exposure change of 1 f-stop. A negative value will decrease exposure and so will have the effect of darkening the image, whereas a positive value will increase exposure and will have the effect of lightening the image. Note that the EV value is calculated by multiplying the aperture value (AV) by the shutter speed (also known as "time value" and denoted by TV). The significance of the EV calculation is that different shutter speeds and different apertures can result in exactly the same EV value, which provides a fair degree of versatility in composing a photo. (see aperture, exposure, metering)
- Field Of View (FOV) - (sometimes referred to as the "angle of coverage") In relation to a camera, describes either the extent of a scene that can be observed through a viewfinder or the extent of a scene that can be captured by film/sensor (usually close to the same). The fov figure represents an angle measured in degrees, such as 30 degrees. It should be noted that the fov can refer to an angle in either a horizontal plane, vertical plane or a diagonal plane, however the horizontal fov is usually specified. The focal length of a camera/lens combination determines the fov. (see focal length)
- Fine Art Paper - A class of paper that is popular amongst those producing artistic paintings, images or photos. In fact, there is a fine art paper to suit almost any application, including "regular" photographs. This class of paper is characterised by its matte (i.e. "unshiny") finish. It comes in a wide range of textures, from highly-textured to highly smooth. The smoother range of fine art papers are capable of reproducing the very finest of detail in an image or photo. This class of paper is synonymous with high-grade, acid-free paper.
- Focal Length - In relation to a camera's optical system, refers to the distance from the midpoint of the lens to the focal point on the digital sensor or film plane. The focal length is usually measured in millimetres. The focal length determines the lens‘ magnification factor as well as the field-of-view (usually abbreviated "fov", and measured in degrees). The greater the focal length, the larger the magnification factor. Also, the greater the focal length, the narrower the field-of-view. Note that a focal length of 50mm (in terms of 35mm equivalent film or sensor size) is approximately equal to the field-of-view produced by the human eye, and results in close to zero magnification (i.e. "neutral" magnification). (see focal point)
- Focal Point - In relation to a camera's optical system, refers to a point (note: in this context, when we mention a "point", we are referring to a horizontal plane, not a dot-like point) at which light rays (originating from some object or scene) converge uniformly, or mostly uniformly, after passing through the lens. An image that is formed from light rays striking the sensor or film at the focal point is said to be "in focus".
(see chromatic aberration, focal length) [focal point diagram]
- Gallery Wrap - (also called a "mirror wrap") In relation to canvas printing, refers to a print that is stretched over a (usually) wooden frame, so that part of the image extends (or "bleeds") over the sides of the frame. Staples or fasteners are applied to the rear in order to remain hidden from view. This is a popular way to present a canvas print. Additionally, canvas prints can be framed conventionally, or hung on the wall using a poster hanger device. (also see canvas stretching, poster hanger and museum wrap)
[gallery wrap example]
- Global Image Adjustment - In relation to the editing of a digital image, refers to any adjustment or correction that is made to an image as a whole, rather than to a specific area. An alternative definition is any adjustment or correction that does not require the application of selections or selection masks within an image editor. An example of a global image adjustment is an increase in the overall contrast.
- Glossy Paper - A class of paper that has a gloss or "shiny" finish. Glossy paper comes in different levels of shininess. Typically, the shinier variants are referred to as "gloss" or "glossy" paper, whereas the less shiny variants are referred to as "semi-gloss", "satin" or "pearlescent" paper. In general, this class of paper is well suited to reproducing the very finest of detail in an image or photo.
- Greyscale - A type of monochrome image, consisting of grey tones (which may or may not include the colours black or white). This type of image is more often referred to as "black and white", although technically, such a description is misleading.
- GSM - An abbreviation of the term "grams per square metre". Commonly used as an indicator of paper heaviness. Note that it is incorrect to use GSM as an indicator of thickness, even though some correlation exists. Typical office printing paper has a weight of 80 GSM. A good-quality photo paper will tend to weigh 200 GSM or more. (see paper thickness)
- Image Resolution - (objective measurement) In relation to an image on screen, refers to the average number of pixels per square inch (abbreviated "ppi") making up the image. The higher the ppi, the higher the amount of visual "information" in the image. As the average number of pixels per square inch increases, color gradations will appear smoother and the edges of objects will appear sharper. Therefore, increasing image resolution (by capturing, creating or post-processing the image at a higher resolution) results in finer detail becoming perceptible.
- Image Noise - Describes the appearance of 'random' grains or particles in an image (usually distributed fairly evenly throughout the image). It may be helpful to think of image noise as being somewhat similar to the grainy looking interference you may have experienced when watching television. There are two types of noise that may affect an image: chroma noise and luminance noise. Chroma noise refers to 'random' grains that appear as a result of fluctuations in colour. Whereas, luminance noise refers to 'random' grains that appear as a result of fluctuations in brightness (i.e. luminance) levels. Of the two, it is chroma noise that has the greater effect in terms of making an image appear unnatural. There are different algorithms that can be applied to an image to lessen the effect of noise. However, it should be noted that, removing too much luminance noise using such algorithms can in itself result in an image appearing 'plastic-like' and unnatural. The level of chroma noise is largely dependant on the performance of the image sensor in a digital camera. However, the level of luminance noise is largely dependant on the ISO film speed setting (or sensitivity setting) used when taking a photo. For instance, a setting of ISO 1600 is likely to result in considerably more noise than a setting of ISO 100.
[image noise example]
- ISO - An abbreviation for the International Organisation for Standardisation. An organisation, based in Europe, responsible for developing standards in a wide range of areas.
- ISO Brightness - (also known as standard ISO 2470) An ISO standard, popular in Europe, Asia and Australia, that is used to measure a paper's 'whiteness'. It is expressed as a value ranging from zero to 100. The higher the value, the whiter the appearance of the paper. Furthermore, the higher the value, the greater the potential contrast for a printed image (see Dmax). The ISO Brightness test involves directing a light with a wavelength of 457 nanometres (which falls within the blue region of the visible spectrum), onto the paper at a specific angle, then measuring the reflected light. It is important to note that ISO 2470 is affected by the presence of optical brighteners in paper. An alternative measurement, TAPPI GE, is not affected to the same degree. The TAPPI GE standard is popular in North America.
- Lens Barrel Distortion - An optical effect (not necessarily undesirable) which results in an image being distorted in a circular manner. The effect will tend to be more prominent towards the outer edges of the photo, with the centre often being unaffected. It is caused by a lens which has lower levels of magnification away from the centre. Lens barrel distortion is a trait of some wide-angled lenses.
[lens barrel distortion illustration]
- Lens Flare - An undesirable optical effect which is characterised by faint-coloured, circular halos appearing in a photo. Lens flare results when light enters at an angle and then bounces around inside the lens (or between lens elements), prior to reaching the image sensor. The presence of bright light sources in front of the lens (but not necessarily in the field of view) is the most common cause. A lens hood can be used to reduce the possibility of lens flare affecting a photo.
[lens flare example]
- Lignin - Refers to a naturally occurring, "glue-like" compound that is found in trees and certain plants. Lignin is responsible for binding wood fibres together. Over time, lignin breaks down and in the process produces acidic substances. Of course, the existence of acidic substances in paper is detrimental to print longevity, and so archivists prefer to use paper that is lignin-free where possible.
- Local Image Adjustment - In relation to the editing of a digital image, refers to adjustments or corrections that are made to a specific area in isolation, without affecting (or with very little effect to) any other part of the image. An example of a local image adjustment is a correction made to a subject with red eye. Another example is the retouching of a subject's face in order to remove a blemish. In general, it is more difficult and time consuming to make local image adjustments than it is to make global image adjustments.
- Matte Paper - A class of paper that has minimal or imperceptible shine. This is a feature typical of fine art paper as well. However, a paper described solely as "matte" will tend to be smooth and will generally not have any significant texture in its finish. Higher-grade matte papers are capable of reproducing the very finest of detail in an image or photo.
- Metamerism - Although technically incorrect, the popular definition of metamerism is a situation whereby the colours in a print appear different when viewed under alternate light sources. As an example, the black colours in a print viewed under yellowish incandescent light might appear dark brown when viewed under whiter fluorescent light. Metamerism does not represent some flaw in a material or ink (although some pigment inks are known to be better than others at minimising the 'effect' of metamerism). Rather, it describes the fact that the colour of most (if not all) objects will display some variation depending on the light source under which they are viewed.
- Metering - (also called ‘light metering’) Refers to the process of obtaining information about the prevailing light conditions by the use of a light meter. The light meter may be an external unit or it may be one built into the camera itself. Virtually all modern dSLR cameras have advanced light meters built into them. The information provided by the light meter is used to determine the appropriate exposure settings (e.g. expose for the shadows and don't worry about blowing out the highlights, or vice versa). Note that, strictly speaking, the ‘metering system’ is not the same thing as the light meter. The metering system also includes the digital processing engine that performs various calculations based on the light meter readings. For instance, based on the prevailing light conditions, the photographer can program in the desired aperture, and then the metering system can determine the required shutter speed (known as aperture-priority mode). Alternatively, the photographer can program in the desired shutter speed, and then the metering system will determine the required aperture setting (known as shutter-priority mode). The metering system can use a number of different "program modes" to determine the required exposure settings. Although the names of these modes may vary slightly, three of the main metering modes are typically known as: average metering, centre-weighted average metering and spot metering. Average metering uses the entire scene to determine the correct exposure. Centre-weighted average metering exposes for the entire scene, however, it places a greater emphasis on the centre 60-80 % of the scene. Spot metering exposes for 1-5% of the scene, typically located at the very centre of the scene. (see exposure)
- MTF - An abbreviation of the term "Modulation Transfer Function". The MTF is a mathematical formula commonly used to determine the actual resolving power (sometimes referred to as the "true optical resolution") of devices such as cameras and scanning equipment, taking into account possible limitations in the optics used in such devices. Although calculation of the MTF value can be performed by hand, it is usually calculated using software. A digital sensor in a scanner may be capable of capturing, say 1200 ppi of data, however the true resolving power of the device may only equate to 900 ppi after mediocre optics are factored in (think of your eye as the digital sensor, and the mediocre optics as a blurry pair of glasses). When providing specifications of low-end scanners and digital cameras, manufacturers almost always specify the resolution of the digital sensor (even though some still refer to it as ‘optical resolution’), rather than stating the true optical resolution. Sometimes, a digitally-interpolated resolution is stated instead of (or ahead of) the digital sensor's resolution.
- Monochrome - Describes a class of images that consist of a single hue of colour. Examples of monochrome images are black and white (i.e. greyscale) photos, as well as the original film-based sepia photos.
- Multisampling - In relation to scanning / photo scanning, refers to a technique whereby an item is scanned (i.e. sampled) a number of times in order to reduce or remove noise generated during the scanning process. Dark areas (i.e. the shadows) of images are particularly susceptible to noise, given that such areas produce a faint signal relative to noise (this relates to the concept in electronics of the signal-to-noise ratio). Therefore, multisampling is particularly useful when scanning images with a significant amount of dark area. Multisampling takes advantage of the fact that noise is random by nature, and is therefore highly unlikely to appear at the same points in subsequent scans. Multisampling involves "averaging-out" the luminance/colour value of each sample/point after it has been scanned a certain number of times (e.g. 2x, 4x, 8x or 16x, sometimes referred to as the "sampling factor"). The greater the sampling factor, the less visible the noise. It should be noted that there are two forms of multisampling. The first, and crudest method, is called multi-pass multisampling. It involves scanning the entire image from start to finish, and then repeating that process according to the sampling factor. The important point about multipass multisampling is that the averaging process only occurs after the entire image is scanned the required number of times. If the scanner's vertical line-feeding mechanism is not perfectly consistent (quite common), or the scanned item moves slightly during subsequent scans, a blurred image will result. Negatives and film are particularly susceptible to movement during multiple scans/passes, due to the often complex way in which they are loaded, and given that they can have curvature/warping issues. Single-pass multisampling overcomes the potential line-feeding problem by performing the multiple sampling during each horizontal pass. When requesting multisampling from a photo scanning service provider, you should ensure that they will use the single-pass technique. (see scanning resolution)
- Museum Wrap - In relation to canvas printing, refers to a print that is stretched over a (usually) wooden frame, so that the entire image appears on the front of the frame and does not extend over the sides. The sides of the frame may be left as unprinted canvas, or they may be coloured black or some other "solid" colour. As with a gallery wrap, staples or fasteners are applied to the rear in order to remain hidden from view. This is another popular way to present a canvas print. Additionally, canvas prints can be framed conventionally, or hung on the wall using a poster hanger device. (also see canvas stretching, poster hanger and gallery wrap)
- Opacity - (also known as "show-through") - In relation to printing, refers to the degree to which paper resists light passing through it. It is the opposite of transparency.
- Optical Brightener - (also referred to as a "fluorescent brightener" or "optical brightening agent"(OBA)). A chemical agent added to paper during the manufacturing stage for the purpose of making the paper appear whiter (or "brighter") to our eyes. Optical brighteners work by absorbing invisible ultraviolet light and, in return, emitting bluish light that falls within the visible spectrum. It is essentially the same technique used to make "glow-in-the-dark" toys. Archivists argue that high-end archival papers (designed to last for decades or centuries) should not contain optical brighteners because these optical brighteners are likely to lose their effectiveness before the "raw" paper and ink combination show any signs of colour fade. In such situations, as the optical brightener deteriorates, the image will develop a detrimental colour shift as the paper's white point returns to its natural state, which will typically be a shift to a yellowish colour. Another disadvantage of the optical brightener is that its use is often a major factor in cases where a print exhibits ‘metamerism’. (also see metamerism)
- Overexposed - A usually undesirable situation whereby a camera's digital image sensor or film was exposed to too much light under the prevailing conditions (i.e. based on the prevailing light and the camera's exposure settings). At the extreme end, an overexposed photo may appear as ‘constant’ white (i.e. ‘burnt out’) in certain regions or in its entirety (this is known as "highlight clipping"). The ‘brightness’ of this white will be determined by settings in the editing software or RIP, the characteristics of the output medium, printer capabilities, etc. Regardless of the tone of white, clipped highlights will be characterised by an absence of detail, and so cannot be corrected by image editing software. Overexposure and highlight clipping is sometimes used for creative effect. Therefore, to a large degree, the term "overexposure" is quite subjective, and depends on what the photographer intended for the photo to convey.
[overexposure examples]
- Panning - In relation to the handling of a camera, refers to a sideways movement, either left-to-right or right-to-left, usually in order to track a moving subject within the viewfinder.
- Panorama - (in relation to the dimensions of a print) There is no agreed standard as to what print dimensions (or aspect ratio) constitute a panorama. Informally, it refers to a print that has one dimension that is 'considerably' longer than the other dimension. Indeed, this description is vague. We would argue that a panorama is any print that has one dimension that is at least two times longer than the other dimension (i.e. with an aspect ratio of at least 2:1, such as a print measuring 24 inches by 12 inches). Notice that we don't refer to the width being two times as long as the length, or vice versa. This is by virtue of the fact that a panorama can extend either horizontally or vertically.
[panorama example]
- Paper Curl - Describes the tendency of a paper print to remain curled after the printing process has completed. The extent of this undesirable curling will largely depend on (i) the roller mechanism employed by the printer, and (ii) the type of paper used, and (iii) the method used to store the print during transit. Ideally, a print should be stored in a flat position, although in reality this may be impractical during transportation. If a print must be curled up, for instance when it must be placed inside a document tube, it is important to select a tube with a diameter that is as large as practical (typically a minimum of four or five inches) in order to minimise the curling effect.
- Paper Sizes (ISO 216) - The ISO 216 standard paper sizes include the popular A-series and B-series. The A-series includes the following sizes:
A7 - 74mm x 105mm
A6 - 105mm x 148mm
A5 - 148mm x 210mm
A4 - 210mm x 297mm
A3 - 297mm x 420mm
A2 - 420mm x 594mm
A1 - 594mm x 841mm
A0 - 841mm x 1189mm
Whereas, the B-series includes the following sizes:
B7 - 88mm x 125mm
B6 - 125mm x 176mm
B5 - 176mm x 250mm
B4 - 250mm x 353mm
B3 - 353mm x 500mm
B2 - 500mm x 707mm
B1 - 707mm x 1000mm
B0 - 1000mm x 1414mm
In general, standard poster sizes are considered to be A3, A2, A1, A0 and B0. However, it should be noted that these sizes do not match the aspect ratio of photographs. Therefore, photographs that are to be printed in one of these sizes will require some cropping. (see aspect ratio, crop)
- Paper Thickness - (also referred to as the paper's "caliper") Paper thickness is often specified in mils. One mil is equivalent to one thousandth of an inch. Premium papers tend to have a thickness of at least 10 mils. (see gsm)
- Paper White Point - The colour (or colour temperature) of paper before any ink/image is rendered on the paper. The white point will represent some shade of white. When a paper is relatively closer to 'true' white, it is described as "brighter", "cooler" or "bright white" . When a paper has some sort of 'yellow' tinge, it is described as "warm" or "warmer". Artists and photographers may deliberately seek out "warmer" coloured papers for the effect they have on a particular photo or image. It should be noted that, in many cases, the difference in white point between various papers is very subtle, even when they are placed side-by-side (of course, this definition ignores 'fancy' coloured papers with highly saturated hues of purple, red, etc).
- Paper Texture - The degree of roughness or coarseness of a paper, both in terms of feel and in terms of its appearance. A paper with a high degree of roughness or coarseness is described as "highly textured". Sometimes also referred to as the paper's "tooth", although this is more often associated with the tactile feel of the paper alone.
- Perspective distortion - An optical distortion (not necessarily undesirable) that results in part of an object appearing to be 'unnaturally' large in relation to another part of the object. Photographers often encounter perspective distortion when photographing the entire facade of a tall building at a close distance. In this situation, the sides of the building will appear to be converging towards the peak. The effect can be reduced by standing further away from the object when shooting. Otherwise, tilt-and-shift lenses can be used to correct for the distortion, as can certain image editing programs.
[perspective distortion example]
- Pigment Ink - A class of ink created by adding very finely ground colourants (derived from solid coloured material) to a liquid solution. The colourants are insoluble - i.e. they don't dissolve in some solution to produce colour the way dye ink does. The colour of pigment ink is produced by the many tiny coloured particles adhering to the top of the paper. The molecules of these pigments are relatively large, making it more difficult for them to break down. The result of this is that pigment ink tends to have superior fade and water resistance compared to dye ink. The main disadvantage of pigment ink is that it tends to have a smaller colour gamut. However, with recent advances, this difference now tends to be quite small, particularly in the high-end printing market.
- Pincushion Distortion - An undesirable optical distortion which results in an image appearing to be stretched (or pinched) inwards towards the centre (think of the inwards distortion you get when you push your thumb down on a cushion). It is caused by a lens which has lower levels of magnification towards the centre. Pincushion distortion is a trait of some telephoto lenses.
[pincushion distortion example and illustration]
- Pixellation - (subjective) Describes an undesirable situation, either in print or on screen, whereby at a typical (or reasonable) viewing distance you notice that your print or image is made up of individual little squares rather than fine gradations of colour. Pixellation results when there is insufficient resolution in a print or image.
[pixellation example]
- Poster Hanger - As an alternative to conventional framing, describes a device used to display a poster. These devices usually consist of a horizontal rod or strip to hold the top part of the poster, and another rod or strip attached to the bottom of the poster which acts as a weight preventing the poster from curling. Poster hangers vary in terms of their appearance, the mechanism used to load the poster and the mechanism used to mount the device to the wall or ceiling. The main advantages of a poster hanger are: (i) it is considerably easier to attach a poster to these devices than it is to frame a poster, and (ii) it is considerably easier to swap prints between these devices than it is to swap prints between conventional frames, and (iii) it offers outstanding "minimalism". Without the bulk of a conventional frame and without the possibility that light will reflect off glass, there is very little to distract from the actual print. The main disadvantage of a poster hanger is that is doesn't offer the same level of protection offered by a frame with a glass cover, although laminating or coating a print can offset this disadvantage to some degree.
- Posterisation - (also referred to as "banding") Describes a situation whereby the colours or tones making up a photo are restricted in a manner which produces sharp (or less gradual) changes in colour or tone throughout the photo. The more extreme cases of posterisation are typically the result of deliberate image editing, with the intention of making a photo appear cartoon-like. The less extreme cases of posterisation are often caused by: (i) unintentional mistakes made with colour space conversions, or (ii) excessive editing of photos that have a "low" bit depth (e.g. 8 bits of colour or tone), or (iii) the conversion of a photo to a higher bit depth, for instance from 8 bits to 16 bits of colour or tone.
[posterisation example]
- Prime Lens - A lens with a fixed focal length (e.g. only 50mm) , as distinct from a zoom lens which has a variable focal length (e.g. 35-70mm).
- Printer Calibration - Refers to the processes used to ensure that a printer produces colours that are consistent in relation to a pre-determined baseline. Over time, printing devices wear and ink and paper formulations vary (even within the same batch of such items). The result of this change in state is that the same digital signals sent to the printer to achieve a specific colour will no longer produce the same colour. Some level of compensation (i.e. correction) is then required to allow the printer to once again print colours that are consistent with the baseline. As part of the processes required to achieve predictable colour, a printer should be calibrated regularly, and at least each time an ink cartridge is changed or paper is loaded.
- Printer Colour Profile - An objective measurement used to describe the colour reproduction characteristics of a printer, ink and paper combination. Colour profiles are typically specified by using an ICC (International Color Consortium) colour profile.
- Print Colour Accuracy - Refers to how accurate the colours of a print are in relation to the colours of another print (i.e. relative to a printed proof) or in relation to the colours of the image on a screen (i.e. relative to a screen proof).
- Print Colour Fade - An undesirable situation whereby the colours in a print fade over time. One of the main causes of colour fade is exposure to light; in particular, ultraviolet light (uv), either through exposure to sunlight or exposure to certain other light sources. Acidic gasses or substance that come into contact with a print are another common cause of print fade (also see acid-free). A third cause is exposure to ozone gas, which occurs naturally but is also produced by certain electrical equipment, such as laser printers or certain air ionisers. Some common methods used to combat print colour fade are: (i) minimise exposure to uv light by physically keeping the print away from uv sources, and (ii) placing the print in a frame with uv-filtering glass or acrylic, and (iii) directly laminating the print with a uv-resistant laminate or coating, and (iii) using fade-resistant inks (i.e. archival inks). Note that framing, laminating or coating can result in significantly lower exposure to ozone gas and significantly lower exposure to acidic substances. (see lignen, coating)
- Print Ghosting - (also known as "out-gassing" or just "gassing") An undesirable situation whereby a picture frame's glass (or acrylic) becomes fogged from the inside. This is usually caused by inkjet prints mounted within a frame that have not been allowed to cure (i.e. dry) sufficiently. In this situation, liquids from within the ink evaporate and then condense on the inside of the frame's glass.
- Print Resolution - (objective measurement) In relation to a printed photo or image, refers to the average number of dots per square inch (abbreviated "dpi") making up the print. The higher the dpi, the higher the amount of visual "information" in the print. As the average number of dots per square inch increases, color gradations will appear smoother and the edges of objects will appear sharper. Therefore, increasing print resolution results in finer detail becoming perceptible. It is important to note that, due to the different physical rendering methods, an image's ppi on screen will rarely equal the image's dpi when it is finally printed. As an example, in order for a dot-matrix printer to render the equivalent of a single pixel shown on screen, it will have to produce a number of dots (i.e. one screen pixel = multiple printed dots). In general, a print with a resolution of 1200 dpi or greater is considered a high-resolution print.
- Print Sharpness - (subjective) The amount of fine detail or visual "information" perceived to be present in a print. The definition (or lack of definition) in edges and lines is often a large factor in our perception of print sharpness. An alternative definition of print sharpness is the degree to which a photo or image rendered on paper appears "unblurry".
- Red Eye - In relation to a photo, an undesirable situation whereby the colour of a subject's eyes appear reddish. This is caused by the light from a flash reflecting off the retina of the eye. The same effect can occur with animals, although, the reflection from the retina will tend to produce a different colour to red. In order to avoid red eye when taking a photo, it is recommended that an external flash is triggered whilst at some distance (within the same horizontal plane, i.e. to the left or right) away from the camera. If the subject in a digital photo appears with red eye, mathematical algorithms within software can be used to make a correction.
[red eye example]
- Scanning Resolution - In relation to digital photo scanning, refers to the horizontal resolution of a scanning device, with the vertical resolution assumed to be exactly the same value. The scanning resolution is incorrectly expressed as dots-per-inch (DPI) by virtually all scanner manufacturers. In fact, what a scanner is actually doing is reading a certain number of analogue samples-per-inch (SPI), which are subsequently converted into the pixels represented by a digital file. Only after the scanner (and the controlling firmware and software) finishes producing the corresponding digital file, does it make sense to refer to pixels-per-inch (PPI) resolution. A scanner's resolution will be stated in a form such us '1200 x 600 DPI'. It is customary to state the horizontal resolution as the lower figure, with the higher figure merely indicating the number of vertical samples read by the device following a single horizontal pass. When assessing a scanner's capabilities, it is important to determine its true optical resolution. That is, it is important to determine the actual resolving power of the scanner, after taking into account limitations in its analogue optical system and without using any subsequent interpolation by firmware or software. Other important performance measures include the bit depth of the scanner's analogue-to-digital converter, which should be at least 48 bits / 16-bits per channel for a high-end scanner (the higher the bid-depth, the greater the potential colour gradations) as well as its dynamic range (determined by Dmax-Dmin). When requesting a scan from a photo scanning service provider, you may need to request a certain custom resolution, in the event that you need the image saved at a specific size (e.g. 3600 pixels by 2400 pixels). (see Dmax, MTF)
- Sepia - Originally, a reference to a type of monochrome film processing method introduced in the late 1800s. It involved adding a pigment, derived from the cuttlefish ink sac, to the positive print of a black and white (i.e. greyscale) photo. The result was a monochrome image with a reddish-brown tone. In recent times, the definition has been widened to include any monochrome or duotone photo that falls in the ‘vicinity’ of orange-brown to reddish-brown. In relation to digital photography, the sepia effect is achieved during post-processing, using either an image editor or a camera's own internal processing engine.
[sepia examples]
- Shutter - In relation to a camera's optical system, refers to an internal mechanism that opens and closes for a specific interval, to assist in controlling (more than any other camera mechanism) the amount of light reaching the digital sensor or film. Depending on camera make and model, shutter speeds can vary from 30 or more seconds ("long" exposure time), to 1/8000 of a second or less ("short" exposure time). The term ‘shutter speed’ is often used interchangeably with the term ‘exposure time’. Shutters are usually built into the camera's body, and sit immediately in front of the sensor or film (known as focal-plane shutters). Focal-plane shutters essentially work by moving a blind with an open slot (it may help to think of a venetian blind with one or more rungs missing) across the sensor or film. The speed of the blind's movement remains constant, whereas the width of the slot is varied to control exposure time. The narrower the slot, the shorter the exposure time. (see exposure, focal point, bulb mode)
- Stretcher Bar - In relation to canvas prints / canvas printing, refers to a bar, typically made of wood, that is used to construct a rectangular frame which is then used as a support for a canvas print. To help minimise the chance of the canvas cracking or creasing, a stretcher bar should have a profiled (i.e. rounded) edge on the upper-outer side that will be in contact with the canvas. In addition, the stretcher bar should be beveled (i.e. it should slope downwards and away from the canvas) on the upper-inner side, with the aim of having the profiled edge as the only part of the frame that is in contact with the front of the canvas. When a canvas print is mounted on a frame that is made of non-beveled bars, what often happens is that, in due time, unsightly crease marks will appear at the front of the print, manifesting themselves as an outline of the inner edge of the frame. (see canvas stretching, canvas prints, canvas)
[stretcher bar example]
- Triptych - A work of art consisting of three physically separate pieces of photography, drawings, paintings, vector art or sculptures (or a combination of these) that are related visually, intellectually or morally. The three pieces are usually arranged either in a horizontal or vertical manner, with each piece juxtaposed. The concept of the triptych has developed over two thousand years, since its early depiction of religious motifs in many cultures.
[triptych example]
- TTL - An abbreviation of the term "through-the-lens". In relation to cameras, describes a metering system (i.e. TTL-metering) that performs its exposure calculations based on reflective light readings that are measured directly through the lens. One of the main advantages of such a system is that it provides more accurate measurements, since it is taking its data from (close to) the same image/scene that is being viewed through the viewfinder and that the film/digital sensor will be exposed to. (see exposure, metering)
- Underexposed - A usually undesirable situation whereby a camera's digital image sensor or film was exposed to insufficient light under the prevailing conditions (i.e. based on the prevailing light and the camera's exposure settings). At the extreme end, an underexposed photo may appear as ‘constant’ black in certain regions or in its entirety (this is known as "shadow clipping"). The ‘darkness’ of this black will be determined by settings in the editing software or RIP, the characteristics of the output medium, printer capabilities, etc. Regardless of the tone of black, clipped shadows will be characterised by an absence of detail, and so cannot be corrected by image editing software. Underexposure and shadow clipping is sometimes used for creative effect. Therefore, to a large degree, the term "underexposure" is quite subjective, and depends on what the photographer intended for the photo to convey.
[underexposure examples]
- Vignetting - (also called "falloff") In relation to a camera's optical system, describes a usually undesirable situation whereby the corners of an image show reduced levels of brightness, sometimes approaching black. Vignetting can be caused by such things as the design of the lens itself, or by a poorly fitted lens hood. Vignetting is sometimes used for creative effect. It can also be introduced ‘artificially’ by using image editing software.
[vignetting examples]
- White Balance - In relation to a digital camera, refers to an adjustment made to a type of 'colour balance' setting, which affects the way the camera's firmware converts the raw image data to a photo format, such as JPEG or TIFF. The white balance essentially tells the camera's firmware what shade of white (referred to as the colour temperature, and measured in Kelvins) to expect based on the prevailing light conditions. It is quite an important setting, because it is used as a basis from which the various colours in the image are calculated. Although virtually all digital camera's have an automatic white balance setting, it can occasionally produce obviously incorrect values. An inappropriate white balance setting will result in a colour cast, and so, unless this is intended for creative effect, it is important to set the white balance to a value that matches the prevailing light conditions as closely as possible. The problem of white balance arises because our brain adapts to the prevailing light conditions so that we can recognise 'white' in a wide range of conditions. This adaptation in human vision can not as yet be easily compensated for using digital equipment alone. The advantage of setting your camera to save a photo in RAW format is that you can subsequently experiment (in a non-destructive way) with a number of settings, including white balance, before the conversion to a photo format takes place. (see colour cast)
- Zone System - A technique for evaluating exposure, invented by Ansell Adams and Fred Archer in 1939. Although originally intended for evaluating exposure based on film photography, the Zone System has been adapted for use in digital photography. The aim of the Zone System is to allow the photographer to control exposure of specific parts of the scene that he or she deems important (i.e. parts of the scene that should contain appropriate detail). The Zone System is particularly useful to landscape and architectural photographers.
- Zoom Lens - A camera lens with a variable (i.e. adjustable) focal length. An example of a zoom lens is the Canon EF 24-70mm f/2.8L USM, which can vary its focal length from 24mm to 70mm. The term ‘zoom lens’ is often confused with the term ‘telephoto lens’. These terms have different meanings. A telephoto lens is one that produces a magnification effect, and so is often designed for photographing distant objects. Note that It need not necessarily be a zoom lens. A telephoto lens is one with a focal length that is greater than the width of the image formed on the digital sensor or analogue film. A common, informal definition of the telephoto lens is one which has a focal length greater than 50mm (in terms of 35mm equivalent film or sensor size), regardless of whether it is a prime lens or a zoom lens. Some of the "longer range" telephoto lenses start at 300mm, with some reaching 800mm or more. (see prime lens, focal length)
Photo Enlargements And Canvas Prints Glossary
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