Troubleshooting Photos – Definitions
Common Terms in Digital Photography & Photo Printing
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Additive color – The additive primaries Red, Green and Blue (RGB) form white light when combined equally; other combinations produce all the colors of the visible spectrum. Additive color produces the color on monitors, televisions and electronic projectors.
Adobe RGB – A color space with a gamut wider than that available with sRGB. Originally designed to encompass the abilities of best-quality photo printers, whose abilities had exceeded the average monitor's in some important areas.
Aperture – The opening in the camera lens through which light passes to the sensor or film. Aperture is variable by regulating the iris, to control the amount of light received in the camera, and thus the exposure. There are a number of secondary effects, the most important being the increase of depth of field that comes with decreased aperture.
Application – Typically, what Windows users call a program is called an application (or app) by Mac users. A software tool to get something done, be it edit a picture, process a word or write a web site.
Application file – An application file is one written in an application or program's working or native file format. For instance, Word's native file format is .doc. Photoshop Elements' native file format is .psd, the same as Photoshop's. This format typically accommodates all the interim and final stages of work on the file, including various stages of undo. File formats like JPEG (.jpg) may look like native file formats, but they are international standards, shared by many devices and software packages; moreover, JPEG should never be used as a working format. More on JPEG and photo formats here. Often referred to as a program file by Windows users.
Artifacts – The scar tissue of image manipulation and the dirty laundry of digital technology, artifacts are visible irregularities that interrupt the illusion of reality in a photograph. The most common of them may be caused by excessive compression or re-compression of a JPEG (see About JPEG), by heavy-handed sharpening (see here for sharpening techniques) or by digital noise in a long exposure.
Autocorrect/Autofix – In an image editing application, a function that applies a correction to a photo without insisting on decisions about how or how much. They range from the relatively simple ability to fix red eyes caused by flash to very sophisticated changes that will bring light into the darkest shadows of your underexposed (too dark) images. They're not foolproof, but you can make them work for you, as explained on this page.
Banding – Banding is the breakup of an area that should be a continuous flow of color into an area of distinct colors or tones. Banding can be a deliberate artistic effect, but it may also result from the image not having enough available colors to render a smooth transition. This may occur because the wrong file format was chosen, as in this example, or because the bit depth is not sufficient to encompass the complexity of the image.
Black point compensation – Black point compensation is a color management function that preserves shadow detail when a photo is translated to a profile with fewer available dark tones than are present in the original image – for instance, when it will be printed on a paper or with inks that can't achieve the true black of the original. Rather than allowing the unobtainable dark tones to be clipped away, and sacrificing shadow detail, Black Point Compensation re-maps the original tone steps into the available tone range. Black point compensation is usually only required when the Absolute Colorimetric intent is selected. See also About Color Management.
Bit depth – Bit depth refers to the degree of color and tone information contained within each pixel. The number of bits captured by current cameras and color file formats ranges from 8 bits in JPEG and TIFF (which yields 256 levels in each of the three color channels) to 14 bits in RAW files (16,384 levels) and 16 bits in some TIFF files (65,536 levels). Increases in bit depth beyond 8 bits per channel, while useful in more complex color editing operations and in finely toned art prints, impose a heavy time burden on photo processing.
Brightness – Color is described by three attributes: hue, saturation and brightness. Brightness is a factor both of the illumination falling on the colored surface and its reflectivity, or when the color is transmitted, the intensity of the source of illumination.
Cast – A color cast is a color that affects all others in a photo. Its cause may be colored light in the scene, most commonly encountered when the reddish light of sunset tinges all other colors, or when the green of fluorescent light permeates every other color. It may also be caused by incorrect selection of the camera's white balance. More subtle casts are possible – photos taken on the water typically have a slight blue tinge while photos taken in a room with strongly colored walls may take on a cast in that color.
CIE – The Commission Internationale de l'Eclairage, aka the International Commission On Illumination. An international standards body, CIE (say see-eye-ee) is the author of standard models used to define what the human eye can see and various means to measure light and color. By defining color and light with scientific precision in what turned out to be a computer-friendly fashion, CIE models laid the foundation for color management (see also About Color Management). On a social note – talking incessantly about CIE this and CIE that is the sign of a Color Bore; remind him that the CIE provided a measuring system for visible light, not a licence to be tedious. Tell him to help you make better pictures or go show off his useless knowledge to someone else (or better, just go – Color Bores typically have a lot of bits of knowledge that they don't really understand, so they can get you totally confused).
CMYK – The colors used in commercial color printing, Cyan, Magenta, Yellow and Black (say see-em-wye-kay). Simple desktop color printers use this set of inks; more expensive photo printers typically use additional variations on these colors (an additional version of cyan and of magenta are common) to give a more comprehensive and pleasing range of color. More on the differences between monitors and print here.
Color correction – Fixing colors to achieve the photographer's objects. Most often, it's natural color: green grass, blue skies and human-color skin with pleasing levels of contrast and definition – but anything is possible.
Color management – Color management is a set of technologies intended to compensate for the limitations and biases of all color reproduction devices (cameras, scanners, monitors, printers). A color management system begins with calibration (making a device do what it's supposed to) then goes on to profile the inevitable bias in recording devices (for instance, noting that a camera records too much yellow) and reproduction devices (for instance, noting that a monitor displays too much blue or a printer lays down too much magenta). With this knowledge, a color management system can warn you that some colors in a picture cannot be reproduced exactly, then go on to translate some or all of the colors into a picture that reflects your intent for the way the picture should look. This page provides a quick intro to color management.
Color profile – See Profile.
Color space – Color spaces are defined portions of the full range of human-visible colors, and provide a reference between color as defined by scientific means by the CIE and color as defined for image-editing purposes. You may know that it's 30 degrees outside but without knowing if it's 30 F or 30 C, you don't know if it's freezing or sweltering. Similarly, the way that color is defined for image-editing purposes is meaningless unless you have a point of reference. An image-editing color definition like R255, G050, B050 (a wholly saturated red, some green, some blue) by itself means little if you don't know which 'red', 'green' and 'blue' are being referenced. A color space provides that reference by defining a space's primaries, and from this information, everything else can be derived, including the real-world appearance of the color created by those values.
Color spaces have been defined with reference to specific reproduction technologies (which may become a problem, because the technologies have moved on).
- the sRGB model specifies the colors that could be displayed in the mid-90's by an average color monitor (and is the default color space used on the Web);
- the Adobe RGB model specifies the colors then achievable by high-quality photo printers;
- the ProPhotomodel specifies all colors achievable at the time of the specification's writing (late 90's) by best-quality cameras and photo printers.
More on the differences between the color spaces can be read on the color management page.
Most point-&-shoot cameras use sRGB while more advanced cameras will also shoot Adobe RGB and ProPhoto, the native space of RAW. To implement color management, a photo-editing program must recognize at least the first two spaces as color definitions depend on their relationship to a color space.
The colors described by photo-editing applications, particularly the saturated ones, are specific to the color space within which they are produced. Put another way, if you change a photo's color space, you will change the look of the photo, sometimes for better, sometimes for worse. A corollary to Murphy's Law states that if you make the change inadvertently and don't notice until too late, it will be for the worse (most color-management-capable programs have warnings you can set to prevent this). If you do it deliberately, it is creative experimentation and may be good, so experiment and let your eye be the guide.
Compression – Photo files are big; compression makes them smaller. A 640 pixel by 480 pixel RGB image is slightly smaller than a half sheet of paper on screen. Uncompressed, it eats almost 1MB of disk space (640 x 480 x the three channels of color, R, G and B). To make photo files more manageable, people developed techniques to reduce file size while retaining the essential picture information. Some forms of compression are applied by a special-purpose compression program, such as those that do Zip compression. Others are applied as part of the file format, such as the optional compression in the TIFF format or the user-definable compression in JPEG.
The most important thing to remember about compression is that it can be lossless or lossy. Use the first type for pictures you're working on (or just don't compress them), the second type for pictures you've finished editing. See also the article About JPEG.
Depth of field – Depth of field is the distance between the nearest and farthest objects that are acceptably sharp in a photo. A smaller aperture gives greater depth of field, a larger aperture gives less depth of field. You can exploit this, either to blur out a background that you don't want in the picture, or show a range of subjects from the foreground to the horizon. See the page on Depth of Field.
DNG – DNG is an open image file format (see also About Formats) – a so-called Digital Negative – developed to address the archive issues presented by the growing number of RAW file formats. Photographers shooting RAW files can convert these files to DNG knowing that future DNG-capable image-editing applications will be able to read them.
DPI – See PPI – Strictly speaking, dpi (dots per inch) is a commercial printing term with a distinct meaning very different from ppi (pixels per inch), but the terms are inseparably confused, even in professional image-editing applications. Unless there is a reason (as in, you're a printer or graphic artist), use ppi when talking about photos.
DSLR – Digital Single Lens Reflex. The single lens reflex portion of the name refers to a design in which light passes through the lens and, via mirror and prism, to a viewfinder. Thus the photographer sees exactly what the camera sees. DSLR's occupy the upper end of the performance/price range; response times are quick, lenses are interchangeable and the electronics include more features. In film days, this type of camera was once totally manual, but DSLR's typically contain all the functions of a point-&-shoot, implemented with greater finesse. Thoughts on their plusses and minuses are included in About Photo Equipment.
Dynamic range – The difference between the lightest and darkest object that an eye or camera can register at the same time. Your eye can smoothly record subjects in bright sunlight while noting items in deep shade, but neither film nor digital cameras can do this. If you set the exposure for sunlight, the shadows will be very dark – perhaps simply black – and if you expose for shadow, the bright areas will simply be detail-less white. Accordingly, some compromises and accommodations such as supplementary lighting or extensive post-processing may be necessary in some photography situations.
EXIF – Exchangeable Image File Format data is embedded in JPEG, TIFF and RAW files taken by digital cameras. EXIF (some speakers spell it out, others say ek-sif) is an automatic record of everything your camera knows at the time you took the picture: date and time of exposure, aperture setting, shutter speed, metering pattern, flash setting, camera make and model, manual settings, even GPS data if the camera is so equipped. Some of this data is nice-to-know, some of it is useful to you in diagnosing what went right or wrong in a picture. Increasingly, software makers are building on this data to help you post-process photos more effectively. Also, there is no longer any reason to disfigure your photos with visible date stamps.
Most cataloguing and photo-editing programs can display EXIF data. It may be shown automatically when you select a photo, or you may have to find a menu item called something like Photo Info (Paint Shop Pro) or File Info (Photoshop and Photoshop Elements).
EXIF data can be lost when saving a file, sometimes by using the Save command, always by using Save For Web. Read the documentation with your software or try saving a copied file several ways to see what deletes EXIF and what doesn't. In any case, always work on copies of your originals.
Format – Photo files can take many forms, including JPEG (.jpg), TIFF (.tif), GIF (.gif), PNG (.png), RAW, and various formats used natively by applications/programs, such as Photoshop's .psd. All have their strengths and weaknesses, depending on what you're using them for. It's important to chose a file format that matches your use. For instance, JPEG files are smaller than many other formats, but some picture information is always lost every time you save a JPEG (see Compression and About JPEG for ways of dealing with this). Application files and TIFFs save losslessly and may save more of your work process, such as layers, but the files are big. More on photo formats here.
Gamut – The gamut is the range of colors that can be represented (e.g., displayed or printed) or detected (photographed or scanned) by a given method or device. It may also refer to the range of colors within a digital file or print. People can see a broader range of color than a photo can record or a printer can print, and understanding a camera's or printer's limitations is an important aspect of achieving pleasing color, either by editing photos or by color management.
Global change – A global change is one that affects the entire image, rather than a portion of it. If you make the entire photo lighter, or if you have made all the shadows lighter, you have made a global change. Generally these are less obtrusive than local changes(for instance, just making the face of one person among a group lighter or less red, which risks isolating the changed portion from the tone and color of the remainder of the photo. Global changes are also less work than a multiplicity of local changes.
GIF – GIF or Graphics Interchange Format (.gif – say giff as in gift) is an old format that is well suited to simple Web site illustrations with areas of single colors, like cartoons or buttons like the ones used to select pictures on this site, but which causes posterization / banding in photos because it only displays 256 colors. GIFs are useful on the Web because the files are compact and because you can make the background transparent. PNG has a similar but broader feature set. More on file formats here.
Hue – Hue is one of the three attributes of color (the others are saturation and brightness) and describes whether something is red, green, blue or a combination. Hue may relate to a specific wavelength within the visible spectrum, but some visible hues, such as magenta, are combinations of two wavelengths.
Intent – See Rendering Intent.
Interest area – The subject, the reason you took the picture, the part you most want to have correctly focused and exposed.
ISO – ISO (say eye-ess-oh) is a means of identifying the exposure index at which a digital camera is operating. Strictly speaking, the term refers to an International Standards Organization method of measuring film speed but the term was borrowed to minimize the mental adjustments required in switching between film and digital cameras. Most digitals operate most comfortably in the same range as film cameras, 100 to 400 ISO (where 400 ISO indicates more sensitivity than 100). Raising the ISO setting from 400 to 800 typically will allow the use of a shutter speed one step higher at the same f-stop (aperture setting). However, at lower light/higher ISO situations, many cameras exhibit color mottling of the image very similar to pronounced grain in film (see Noise).
JPEG – JPEG (filename extension is .jpg – say jay-peg) is a photo file format widely used in digital cameras, on various types of picture CD's and on the Web. It is a lossy file format. JPEG has been extended to make it more friendly to interchange between cameras, the Web and computers, and to allow the inclusion of EXIF data. See also About Camera & Photo File Formats.
Lab – Like RGB or CMYK, Lab (say ell-ay-bee) is a method of representing color. The letters refer to the Luminance of the image (whether it is light or dark at any point), its a channel, which represents colors ranging from green to red and the b channel, which contains colors ranging from blue to yellow. Lab (available in most full-featured image-editing applications) is very useful for some color-correction and sharpening operations.
Local change – A local change is a modification to a limited part of the picture. Using the selection tool on a scene, then sharpening an object that shallow depth of field has rendered slightly blurred is an example of an acceptable local change. Some people, however, will color-correct a picture object by object, with the result that every portion looks a bit different. Lots of local changes, too, are much more work than global changes.
Lossy – A class of file compression, lossy compression typically reduces file size by simplifying some of an image's less important picture information. The most common lossy compression format is JPEG, which allows you to define the level of compression that will be applied (read a fuller discussion in About JPEG). The JPEG codec (compressor / decompressor) looks for areas that are similar and makes them more similar, so they can be described in the same terms, then creates compact descriptions of all the similar areas. This makes a much smaller file, but some picture information is discarded every time a JPEG is saved, particularly if a high level of compression is used. Pictures should not be saved more than absolutely necessary in a lossy compression format like JPEG or you will start to see degradation of the image and artifacts. See About JPEG for ways of dealing with this.
Lossless – A class of file compression, lossless describes a compression method that enables a file to be compressed then decompressed into an exact copy of the original. Also see Lossy.
Megapixel – One million pixels, usually expressed as 'a 6-megapixel camera' or 'a 7-megapixel camera'. Used this way, it is a measure of the maximum size of image that a camera can record; this is only a small part of the quality of the image. A camera that can shoot a maximum-size image of 3070 pixels wide by 2300 pixels high would be described as a 7-megapixel camera (3070 × 2300 = 7,061,000 pixels). See also About Buying Photo Equipment and About the Printable Size of Photos.
Metadata – Information about the photo file, carried as an internal appendix to that file. See EXIF and the tags of TIFF.
Metamer – Metamers are pairs of colors that appear identical under one set of lighting conditions, yet differ under another. Colors that appear identical under fluorescent light often look different in sunlight, for instance. A related condition is color inconstancy, where a change in lighting causes a single color to change noticeably. Dye enhancers called optical brighteners, often found in sports clothing, sometimes make your subject's clothing light up like a bike reflector when you take a flash picture.
Native format – See Application file. More on photo formats on this page.
Noise – Image noise comes from a variety of sources but is most often seen as a fine spotty effect in photos taken in low-light exposures. This happens because there is so small a signal being produced by light striking the camera sensor that its signal is matched or overwhelmed by the signal produced by the sensor's own internal workings. Think of it as akin to the hum made by a sound system when the sound source is faint or off, but the system volume is high. Your camera may have a noise reduction setting for long exposures (check the manual). Also check your image-editing application for a noise filter.
Non-lossy – A class of file compression; see Lossy. Lossless, immediately above, means the same and makes more sense as a word than non-lossy, but some people enjoy saying non-lossy.
Pixel – Short for 'Picture Element', 'pixel' is commonly used to describe a recording point on a camera sensor or the output from that point, which is tone and color information that represents a minute part of an image. By themselves, pixels in photos are pure information about the image; they do not have dimensions until a size relationship is assigned by the computer that is displaying them or the printer that is printing them. For instance the pictures on the first page of this site are 450 pixels by 341 pixels, which display at about 4.5 by 3.5 inches on a 96 pixel-per-inch monitor, but print at the size of a postage stamp at the standard 300 pixel-per-inch print resolution.
PNG – PNG (Portable Network Graphics; you're supposed to say ping, but many people say pee-en-gee) is a file format that was developed in response to patent problems with GIF. In the development process, PNG acquired a number of attractive features for the display of Web and other graphics, discussed on the World Wide Web Consortium pages (search for PNG within the site). The only problem with PNG is that some older browsers don't support it. More on file formats here.
Point-&-shoot camera – A camera, typically pocket- or purse-sized and thus more portable than a DSLR camera, with auto-focus, auto-exposure and a variety of other automated functions to isolate the user from the technicalities of photography and allow him or her to concentrate wholly on framing the picture. Few if any manual functions. Looked down on by camera snobs but capable of taking good photos if you respect their limitations. Thoughts on their plusses and minuses are included in About Buying Photo Equipment.
Post-processing – Messing around with your photos in an image-editing program until you've either fixed them to your satisfaction or gotten fed up with them.
PPI – Short for Pixels Per Inch, ppi is a measure of the information density in a photo. A print made at 300 ppi has 300 points of information vertically and horizontally for each inch of surface, which obviously gives it greater ability to shape and model a subject detail than a picture made at 150 ppi. The more pixels per inch you have in a picture, the more information and therefore the more detailed and lifelike an image will be formed. Unfortunately, ppi and dpi (which is properly a measure for material that is being prepared for a printing press) are often used interchangeably. In photography, it's better to use ppi.
Profile – A profile (also referred to as a color profile, ICC profile or Colorsync profile) is a detailed description of a camera, a monitor or printer's ability to reproduce color, used in the process of color management. See also About Color Management.
Program – A set of codified instructions whereby the computer and occasionally the user conspire to get something done. An application to Mac users.
Program file – A program file is one written in a program's working or native file format. For instance, Word's native file format is .doc. Photoshop Elements' native file format is .psd, the same as Photoshop's. This native format typically accommodates all the interim and final stages of work on the file, including various stages of undo. File formats like JPEG (.jpg) may look like native file formats, but they are international standards, shared by many devices and software packages; moreover, JPEG should not be used as a working format. More on JPEG and photo formats here. Often referred to as an application file by Mac users.
Prophoto – A wide-gamut color space supported within RAW files and by top-quality photo printers.
Puddling – Puddling is the breakdown of a continuous ink film on a print into distinct small drops. Usually caused by specifying the wrong paper type in a print dialog, so excess ink is deposited on the paper. An extreme instance is shown here.
RAW – RAW (it's usually written in caps like an acronym, but it's not initials for something else – just say the word raw) is not a file format but a type of output file for digital cameras. A RAW file is simply the unpolished data that streams off the camera's chip when you squeeze the shutter button. The virtues of RAW files are that you get all the data that the chip is capable of delivering, plus your final image won't be shaped by the decisions you made while shooting; you can continue to manipulate the image until it suits you or until you get sick of it. The downside is that RAW files are large and they require more work back on the computer. More on RAW and other photo formats on this page.
RGB –Red, Green & Blue (say arr-gee-bee) are the additive primary colors. Combined equally, they form white light; other combinations of equal or different intensity combine to form all the colors of the visible spectrum. Monitors display RGB color; desktop color printers use RGB, which they convert internally to ink colors. More on the differences between monitors and print on this page.
RGB printer – Strictly speaking, there's no such thing – RGB is for additive-color devices like monitors – but desktop printers including photo printers work from RGB files, so they acquired that name to distinguish them from the specialized printers used for proofing (testing) files intended for printing on a commercial printing press. The term used to be dismissive, but desktop photo printers now have much broader color gamuts than CMYK printers because they typically have a wider range of ink colors to work from – six and eight are common in photo printers. Sending a CMYK file to an RGB printer will yield unpredictable results.
Reciprocity – For any given scene, there are several possible combinations of shutter speed and aperture, all of which will yield a correct exposure – a fast shutter speed combined with a wide-open aperture, a slow shutter speed combined with an irised-down aperture or something in between. The first will yield shallow depth of field while the second will provide much greater depth of field; as compositions, the two photos will be markedly different. Camera controls are arranged so that if you get a correct exposure at, for instance, f4 at 1/90 sec., you will get the same correct exposure at f5.6 at 1/45 sec. (the aperture allows in only one-half the light, but the shutter is open twice as long). This relationship is known as reciprocity. Digital cameras typically have a P or Program mode that allows you to vary aperture and shutter speed in reciprocal lockstep, to get correct exposure at high speed with little depth of field, or slow speed with better depth of field.
Rendering intent – Rendering intent describes the four modes by which color management systems adapt some or all colors in a picture to the limitations of a given display or printer.
Resampling – Resampling is changing a picture's pixel dimensions by adding or subtracting pixels while maintaining the photo's credibility. If you are enlarging a picture (sometimes called 'upsampling'), your image editing application creates new pixels of a color and lightness that are a weighted average of the adjacent or surrounding pixels. In reducing a picture's size (with remarkable consistency, sometimes called 'downsampling'), the image-editing application generates a pixel that is the average in color and lightness of the pixels being replaced. The averaging process is called interpolation and the larger the number of pixels that are considered in this process, the better the resulting photo will look. More on resampling in About Resizing Photos I – How and About Resizing Photos II – Why.
Resolution – Broadly speaking, resolution is the amount of detail that a camera, your printer or ultimately, your print is capable of recording or displaying. In the camera, it's mainly determined by the number of pixels on the sensor that captures the photo (and to some extent by the bit depth of the file it records). On a monitor, resolution is determined by the number of pixels on the screen. In a printer, resolution is determined by the number of pixels it can print per inch or per centimeter. In a photo, the print resolution is determined by the number of pixels printed per inch or per centimeter. The resolution of a photo, its pixel dimensions, can be changed by resampling it (either to increase or decrease those dimensions), but increasing pixel dimensions this way will not create the detail that would have been captured if the photo had been taken at a higher pixel-dimension setting.
Saturation – Saturation, one of three attributes of color that include hue and brightness, expresses the degree to which a color is one wavelength, without the addition of white or other wavelengths of light.
Sensor – The sensor in a digital camera is the light-sensitive chip that records an image as you press the shutter button. Small point-&-shoot (p-&-s) cameras use a smaller sensor than DSLR cameras and this accounts for some of the difference between the image quality of the two types. Bear in mind that this is a relative difference – you can still take much better pictures with a good digital p-&-s than with a p-&-s film camera.
Sharpening – Sharpening is a simple illusion that makes the edges of objects in your pictures more prominent. This makes the picture look more crisp, always a benefit if done carefully. Sharpening can even hide minor focusing errors. Your image editing application may call it 'Sharpening' or 'Unsharp Masking' (also known as just USM). Unsharp Masking usually provides more control over the process. Excessive sharpening produces odd-looking photos. Your camera probably gives you the option of doing this in the camera; you'll get better results if you turn the in-camera function right off and do it on your computer. See the Sharpening page.
sRGB – A subset of RGB, sRGB (say ess-arr-gee-bee) is an HP- and Microsoft-authored color space that includes all the colors that can be rendered by an average color monitor. sRGB is the default color space of the Web and of most digital cameras (many cameras can work with others, but they are usually shipped set to sRGB).
Subtractive color – Subtractive color is the color model that describes the effect of ink or other colorants on paper. The subtractive primaries are formed by subtracting an additive primary color from white light. Thus,
- white – red = cyan (blue + green);
- white – green = magenta (blue + red); and
- white – blue = yellow (red + green).
The subtractive primaries are the core colors of commercial printing (CMYK) and of photo printing, but in photos, this range is extended by the addition of modified versions of the original four inks.
Tone – The amount of light in any area of a photo; synonymous with 'shade' as in 'shades of grey'. Sunlit areas are light or high tones, shadows are dark or low tones. The eye is more sensitive to changes of tone than changes of color.
TIFF – Tagged Image File Format or TIFF (filename extension .tif – say it like the first part of Tiffany) is a photo file format widely used for photo-editing because it's broadly supported, hence universally exchangeable, because it's lossless and because it's reasonably compact when used with its built-in compression capabilities. The tagged part refers to its ability to include informative 'tags' relating to copyright, a caption, color management settings, etc. More on photo formats here.
Unsharp Masking – Unsharp Masking (sometimes called just USM) refers to sharpening. A confusing term, it derives from a pre-electronic method for making photos look sharper by re-photographing them through a slightly blurred or 'unsharp' mask. Sharpening is not a one-size-fits-all process – correct sharpening depends on variables like the photo size, viewing distance and whether the photo is to be printed, projected or displayed on a monitor. See the definition of sharpening and the Sharpening page.
White balance – White balance is a camera setting for the color of light in the area where the photo is taken. For instance, mid-day summer light contains all colors equally; it's really white light. Incandescent light has more red and yellow, while fluorescent light has a lot of green, so people shot under incandescent light will be more red and when under fluorescents, rather green. Most digital cameras now sense the color of light and make a correction for it, so the light usually appears white and the picture's people and objects are the right color.
Workflow – Workflow refers to the sequence of processes required to print a graphic or photo file, such as copying the files from the camera, cataloging them, correcting their flaws and then forwarding them to their destination (printer, web page, etc.). Because of the number of files they have to get through every day, graphic artists and professional photographers put considerable effort into standardizing and optimizing their workflows.
Zoom – Zoom refers to a lens' ability to change its focal length. A zoom lens can change from wide-angle (able to take in a broad scene while close to the subject) to telephoto (able to bring distant subjects closer at the expense of having a narrower field of view). Properly speaking, setting the focal length is something done in the lens, so the scene fills the full image area. Camera makers now sell something called 'digital zoom', which is really only a form of in-camera enlargement of a portion of the scene. This may enlarge the subject, but the quality is significantly lower than the same photo taken with a real telephoto lens.
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