Digital Darkroom Glossary

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(lens) aberration: Any distortion in an image caused by a lens' inability to properly reproduce an image. Some common forms of aberration are: barrel distortion, pincushion distortion, spherical and chromatic aberration.
absolute colorimetric: A rendering intent used to convert out of gamut colors. For in gamut colors, maps color to color between source and destination color spaces. For out of gamut colors, remaps the color to the closest in gamut color. Does not remap source white to destination white but rather converts white as a color, so whites may look different once converted to the destination color space. To learn more about the Absolute Colorimetric rendering intent, read the Photoshop Color Settings page.
achromatic: Lacking hue and saturation. Having color only in the neutral grays, whites and blacks.
ACR: Unofficial acronym for Adobe Camera Raw.
acutance: The sharpness of edges in an image.
alpha channel: That part of an image file where selection and layer mask information are stored. Both selection and layer mask information are stored in an alpha channel as a grayscale mask. There can be many alpha channels for a single image. Alpha channels are also used to store layer opacity information. However, that is not discussed in detail in this web site. Alpha channels used for selections and layer masks can be seen in the Photoshop Channels palette. However, a layer mask alpha channel cannot be seen in the Channels palette unless the layer is the active layer. For more about using alpha channels for storing selections, read the Savings Selections page.
apochromatic: A lens that is corrected for both spherical and chromatic aberrations.
aspect ratio: The ratio of width to height. 35mm film has a dimension of 36mm wide x 24mm high. This gives an aspect ratio of 3:2.
astigmatism: A lens defect that prevents it from refracting light to form a sharp image.
art: A non-functional, non-practical product (other than aesthetic) of human creativity that touches or stirs one's emotions. If it stirs one to action, or to try to right a wrong, it is more a news feature or a documentary, than pure art.
artifact: Any missing, incomplete or extraneous pixel data in an image caused by data conversion. The most common form of data conversion that can create artifacts is lossy file compression, such as JPEG. In simple terms, lossy file compression discards pixels when creating or saving a file. When the file is opened for processing, the algorithm works in reverse and restores the discarded data. This delete/recreate process can lead to an image having superfluous pixel data, known as artifacts.

Whereas noise is created during signal conversion, artifacts are created during data conversion.

barrel distortion: A lens aberration that causes straight lines in an image to bow outward, especially near the edges. Compare to pincushion distortion.
bit: Data is stored in computing hardware using discrete units known as bits. A bit is the smallest unit of information a computer can store. A bit has a single on/off value. It takes several bits grouped together, called a byte, to store letters and numbers.
bit depth: Channel bit depth is the number of computer bits per color channel used to store color and tonal information. Pixel bit depth is channel bit depth times the number of individual color channels. For more information, read the Channels and Bit Depth page.
bitmap image: The technical term for bitmap images is raster images. Raster images are composed of pixels. Raster images are resolution dependent because the amount of detail is dependent on the number of pixels. The most common way to store digital photographs is as a raster, or bitmap, image because of its ability to store gradual changes in tone. Compare to vector graphic.
black point: The tone at which a printer can no longer distinguish between it and darker tones. For more in depth information, read the Printer Black Point page.
black point compensation: Tells the color space conversion engine whether or not to adjust for any differences in black between the source and destination color spaces. To learn more about black point compensation, read the Photoshop Color Settings page.
bpc: bits per channel
bracketing: A technique used to take several photographs of the same subject in sequence at slightly different exposure settings. The purpose is to increase the chances of getting a properly exposed image under difficult lighting conditions.
brightness: The amount of light being reflected off an object. Same as lightness. Compare to luminance and tone.

capture: To record an image digitally. Either by taking a picture with a digital camera or by scanning film or print.
CCD: Charge Coupled Device. One type of sensor in a digital camera.
CF card: Compact flash card.
chromatic: Having to do with color or colors.
chromatic aberration: A color fringe that appears along edges in a photograph. Caused by a lens' inability to focus different color wavelengths onto the same plane on film or digital camera sensor.
clipping: When an image has been over or under exposed to the extent there is a significant loss of detail. When plotted in a histogram, clipping is seen as a bunching up against the edge of the histogram. For more in depth information, read the Histogram page.
CMOS: Complementary Metal Oxide Semiconductor. One type of sensor in a digital camera.
CMYK: A color model based on the reflective properties of light that stores color information as four color channels of cyan, magenta, yellow and black. Cyan, magenta and yellow are subtractive, or secondary, colors. As light strikes ink on paper, some colors are absorbed (subtracted) from the light while others are reflected. It is the reflected light that we see. The CMYK color model determines what we see by controlling what is removed by absorption. Compare to RGB.
codec: Coder-Decoder. 1. In the telecommunications industry, it is any technology that converts data from analog-to-digital and from digital-to-analog. See modem. 2. In the audio-video industry, in addition to converting audio and video tracks to and from analog and digital signals, it can also be used to compress/decompress the signals. 3. In the digital photography industry, it is a computer program (i.e. software module) that decodes a camera manufacturer's proprietary Raw format such that the Raw file can be read by non-manufacturer software. For example, many camera manufacturers provide codec software so that your computer's operating system may read their Raw file format.
color balance: An image's overall color bias toward a primary or secondary color. For information about adjusting an image's color balance, read the Color Balance page.
color cast: An unwanted color balance.
color channel: A color channel stores the color and tonal information for one of the colors in a color model. For example, the RGB color model has three color channels; one for red, one for green and one for blue. The red information is stored in the red channel, the green information in the green channel and the blue information in the blue channel. All three channels blended together create our image. In the Adobe Photoshop Channels palette, channels are represented as black and white masks. For more in depth information, read the Channels and Bit Depth page.
color correction: As used in this web site, is the removal of unwanted color casts by neutralizing blacks, grays and/or whites. Refer to the Levels Color Correction page or the Curves Color Correction page for color correction techniques.
color gamut: The specific colors in a color space. For more in depth information, read the Profiles and Color Spaces page.
color management: The hardware, software, techniques and processes used to maintain control of color reproduction.
color mode or model: A high level category of how color and tonal information is represented. Grayscale, RGB and CMYK are examples of color models. For more in depth information, read the Profiles and Color Spaces page.
color profile: There are two types of profiles: device and file. A device profile, such as printer and monitor profiles, tells hardware and software how to interpret and render color and tone based on an image file's color profile. An image file's color profile tells hardware and software what color space is associated with the image. A color space is a predefined set of visible colors. For more in depth information about profiles, read the Profiles and Color Spaces page.
color range: A series of one or more colors that are contiguously located on the color wheel. An example of a narrow color range is the reds. An example of a broader color range is the cyans-blues. To read how a color range is different than a color channel, read the Color Ranges and Color Channels page.
color replacement: The changing of an object's hue without changing the object's underlining tone and texture.
colorimeter: An instrument used to quantify the red, green and blue components of emitted light. Often used in the creation of monitor profiles. Compare to spectrophotometer.
color space: A predefined set of visible colors. sRGB and Adobe RGB (1998) are examples of two different color spaces. However, both are members of the RGB color model. For more in depth information, read the Profiles and Color Spaces page.
color tag: The embedded color profile in an image file .
color temperature: A measure of the color balance of light stated in the kelvin temperature scale. For example, 6500 K.
color wheel: A graphical representation of the color ranges found in the visible portion of the electromagnetic spectrum (i.e. light). A color wheel is similar to a pie chart. Each ‘slice’ represents a specific color range. Because it represents the color spectrum laid out in a circle, the primary and secondary colors will be opposite each other in the wheel . Color wheels do not have a fixed number of slices. They have as many slices as the author needs to show. The position on a color wheel is represented by degrees, ranging from 0° to 360°. Since it is a circle, the color range at 0° and 360° is the same. Going clockwise around the circle is positive degrees. Going counterclockwise is negative degrees. For example, if red is 0°, then yellow is + 60° and magenta is - 60°. To read more about the color wheel, read the Light page. To read more about color ranges, read the Color Ranges and Color Channels page.
CompactFlash card: See memory card.
complementary colors: Colors that are opposite each other on the color wheel.
component channel: See color channel.
composite channel: The individual, or component, color channels blended together. See color channel.
contrast: An indication of the difference in brightness between the lightest and darkest areas of a scene, negative, slide, image or photograph. High contrast in a scene means a larger difference in brightness between the lightest and darkest areas as compared to low contrast.
crop: 1. To intentionally leave off (crop) one or more edges of an image while editing. If the edges contain undesirable or distracting elements, this technique can be used to eliminate them. 2. To compose the image in the viewfinder in order to leave out extraneous objects.
cyan: A complementary color consisting of the primary colors green and blue. This text is in cyan.

daguerreotype: The first commercially successful form of photography. Invented in the 1830s in France. Named after Louis-Jacques-Mandé Daguerre.
demosaic: A mosaic is a pattern composed of contiguous, same-sized squares or rectangles that form one large square or rectangle. A chess board is a mosaic pattern. A digital camera's sensor is also a mosaic pattern. Contrary to popular belief, even though a digital picture is composed of image pixels, a camera's sensor is not physically composed of image pixels. It is composed of photosensors arranged to form a mosaic pattern. Each photosensor can record only one color. These photosensors are also known as sensor pixels. Whereas an image pixel contains the complete color and tonal information for a single point in a photograph, a sensor pixel contains the information for only one color. The process of interpolating and combining sensor pixels and converting them into image pixels is known as demosaicing.
depth: The impression of distance.
depth of field: The area on either side of the plane of focus that is in acceptable focus. The part of an image, from foreground to background, that is in acceptable focus. It is a function of aperture size, subject magnification and camera to subject distance.
desaturate: To remove the dominance of any particular hue. The result is no color other than black, white or a shade of gray. To learn about the Tone Management System desaturation method, read the Tone Management System Measured Luminance page.
destructive: Any image editing technique that permanently alters pixels. Not all destructive techniques are bad. Resampling an image to be larger or smaller is destructive, but is commonly done.
detail: Any and all parts of an image with distinguishable characteristics due to differences in hue, saturation and/or tone. For example, smooth, single color paper will have no detail. Coarse paper will have detail because the coarseness causes variations in tone (and possibly hue) which gives the perception of texture.
DICOM: Digital Imaging and COmmunications in Medicine. A medical imaging standard.
digital art, photograph-based: 'Photograph-based digital art' is this web site author's term for a photographic image that has been so heavily modified in the digital darkroom that the image no longer resembles a traditional photograph.
DNG: Digital Negative. An open source Raw format developed by Adobe. For more information about file formats, read the File Format page.
document: Adobe Photoshop's term for an image file.
dot gain: When a printer's ink hits paper, some spreading and absorption occurs. This causes the actual size of the ink dot to be larger than its theoretical size. The gain in size is measured as a percent and is referred to as the dot gain. Matte papers usually show more gain than glossary papers.
dpi: Dots per inch. A means for denoting printer/print resolution. For more about resolution, read the Resolution page.
DSLR: Digital Single Lens Reflex Camera.
duo tone: Grayscale images colorized with two colors. One color is applied to a specific part of the tonal range, such as mid tones, and the other color is applied to a different part of the tonal range, such as highlights or shadows. If three colors are used, it is referred to as a tri tone. If four colors are used, it is referred to as a quad tone.
dynamic range: The ability of film, sensor or paper to capture smooth gradations of tone across the entire tonal range. All films and sensors can capture black and white, which are the extremes of the tonal range. Dynamic range is an indication of how much between black and white can be recorded. A narrow dynamic range means less of a complete tonal range can be reproduced as compared to a wide or broad dynamic range. Images with a small dynamic range have a tendency to appear contrasty because fewer tones can be captured.

EXIF: EXchangeable Image File. While the name has the word file in it, it is not a file per se. It is metadata contained within an image file. It is widely used by digital cameras to store image metadata. In addition to typical metadata, such as resolution and color space, it includes the camera's settings (such as shutter speed, ISO, etc.) when the image was captured. Compare to XMP.
exposure: The total quantity of light reaching film, sensor or paper. Total quantity is a function of the amount of light and how long that amount of light is allowed to touch the medium. In a camera, the two main controls of exposure are shutter speed and lens aperture.

f-stop: 1. Focal length stop. 2. A refracting lens' focal length divided by the aperture's diameter. 3. A value corresponding to a specific aperture size in a lens and the amount of light that passes through the lens. In the same light, a given f-stop represents the same quantity of light regardless of the lens' focal length.
file format: Denotes how pixels are arranged and stored in a file. For more in depth information about the various file formats, read the File Format page.
flash memory card: See memory card.
firmware: Software embedded in hardware.
form: Shape with depth. It is three dimensional. It is best shown using sidelight because sidelight creates shadows which are essential for depicting three dimensions in a two dimensional image.

gamut: See color gamut.
gaussian: A non-linear distribution. The Gaussian distribution in statistics is a normal 'bell shaped' distribution that results when using weighted averages.
giclée: French word meaning 'squirt' or 'spray'. A term used to convey a high quality print made on an ink jet printer using fine art grade paper and archival inks. Occasionally used, inappropriately, to conceal the fact the print was made on an inkjet printer.
golden rectangle: A rectangle that can be divided into a square and another rectangle with the second rectangle having the same aspect ratio as the original rectangle. A golden rectangle has an aspect ratio of 1.618:1. This ratio is also known as Phi, after the Greek sculptor Phidias (493 - 430 BC) who studied the concept. The shape of a golden rectangle is considered pleasing to the human eye. The United Nations Secretariat building in New York City, USA is a golden rectangle. 35mm film, which has a dimension of 36mm x 24mm, has an aspect ratio of 3:2. If a 35mm image were to be cropped to the shape of a golden rectangle, its dimensions would be 36mm x 22.25mm.
gray card: A cardboard or plastic card where one side is a solid, neutral, 18% reflectance gray and the other side is the same gray or white. The gray side represents the exact midpoint of the tonal range from white to black. Used in photographic sessions to calculate exposure by reading the light being reflected off the card using a reflected-light meter. They come in various sizes, but 8 x 10 inches is common.

HDR: High Dynamic Range.
histogram: A graph that plots the distribution of an image's tones across the digital tonal scale. The X axis is the digital tonal scale with black (0) on the left and white (255) on the right. The Y axis is the relative quantity of the number of points in an image that fall into a digital tone. For more information, read the Histogram page.
hue: One of the three characteristics used to describe light in a tristimulus color model. The other two are saturation (also known as chroma) and tone (also known as brightness, lightness, or value). Hue describes the base color, regardless of its saturation or tone. Words such as red, green, yellow, blue, purple, etc. are how we denote hue.

ICC: International Color Consortium. An association that "promotes the use and adoption of open, vendor-neutral, cross-platform color management systems".
indexed color: A color model where color information is stored in a lookup table instead of in individual pixels. Each pixel will have an indexed reference to the table to denote its color. Indexed color images can have at most 256 colors. GIF files use an indexed color model.
IPTC: International Press Telecommunications Council. A UK based consortium of major news agencies, news publishers and news industry vendors that develops and maintains technical standards for improved news exchange.
ISO: International Organization for Standardization. A world-wide network of national standards institutes for establishing weights, measures and other standards for businesses and governments. In photography, the ISO measure is a numeric rating that denotes film's or sensor's sensitivity to light.

JPEG: A digital file format. The JPEG standard, originally developed in 1986 by the Joint Photographic Experts Group (hence, the name JPEG), defines various ways for storing digital image files as small as possible. To learn more about digital file formats, read the File Format page.

K: 1. Abbreviation for the color black, as in CMYK. 2. The symbol for the kelvin temperature scale. The kelvin scale is often used in imaging as the measure of the color balance of light. For example, 3200 K is the color temperature of tungsten and 5500 K (pronounced 5500 kelvins) is considered the color temperature of daylight on a sunny day at noon. While the degree symbol and the word degrees are used with the Celsius and Fahrenheit temperature scales, they are not used with the kelvin scale. 3. The symbol for kilo, or 1000, when expressing decimal values. 4. When used to express computer storage, memory or file size in binary values, the symbol represents 1024, not 1000. For example, one kilobyte is 1024 bytes, not 1000 bytes. Kilobyte is sometimes abbreviated as Kb or KB.

latitude: The tonal range of film, sensor or paper.
light: The visible part of the electromagnetic spectrum. To learn more about light, read the Light page.
lighting: The quality, direction and quantity of the light being photographed. Quality is the difference between the color balance of the light being photographed and the color balance desired by the photographer. The closer they are, the higher the quality. Direction is described as front light, back light, side light, overhead light, etc. Quantity is how much light there is.
lightness: The amount of light being reflected off an object. Same as brightness. Compare to luminance and tone.
lossless, non-lossy: A type of file compression that retains all file data while reducing the file into a smaller size.
lossy: A type of file compression that deletes some data or pixels in order to compress the file into a smaller size.
luminance: The measurement (quantification) of an object's brightness/lightness. Same as tone.
luminance, measured: Tone as measured by the Photoshop Curves control. For more in depth information about perceived and measured luminance, read the Perceived and Measured Luminance page.
luminance, perceived: Color (specifically hue and saturation) can affect the way people perceive which tones are darker/lighter than others. People generally perceive blue to be lighter in tone than green even though they may in fact have the exact same luminance. For more in depth information about perceived luminance, read the Perceived and Measured Luminance page.
luminosity: An object's brightness/lightness. The quantification of an object's luminosity is its luminance.
LUT: Look Up Table. A table containing a cross reference between an index value and a color value. Color models like RGB and CMYK store color information in each pixel. Images using the indexed color model store color information not in each pixel, but in a lookup table. Each pixel will have an indexed reference to the table. The index points to the color value. The indexed color model allows images to have very small file sizes. However, indexed color images can only have 256 colors. GIF files use an indexed color model.
LZW: A lossless, file compression method named after Abraham Lempel, Jacob Ziv, and Terry Welch, who invented the compression algorithm.

magenta: A complementary color consisting of the primary colors red and blue. This text is in magenta.
master file: The non-flattened image file that contains the full image with all corrections and adjustments. The primary purpose of a master file is to create the image we envision using non-destructive techniques whenever possible. Compare to scan file and print file.
megapixel: Million(s) of pixels. 1 megapixel is one million pixels. 2.5 megapixels is two and a half million pixels.
memory card: A small, portable, power free, digital storage medium that uses specialized computer memory chips enclosed in a thin plastic case to store data, audio and image files. Also known as flash memory card. Being power free, the data and image files remain intact on the memory card even when the card is removed from its master device, such as a digital camera. The two most common sizes and formats of memory cards used in digital photography are SD (Secure Digital) and CompactFlash.
memory color: A color, or colors, that most people (in a given culture) would recognize as being correct based solely on past experience, such as the color of gold.
metadata: In digital photography, it is the information about an image, such as resolution, dimension, color space, bit depth, etc. This data is either stored in the image file itself or stored in a separate file, such as the Photoshop XMP file.
mil: An industrial unit of measure for specifying the thickness of coatings, paper, plastics, etc. 1 mil is equal to .001 inch, which is 0.0254 millimeters.
modem: A hardware and software device that modulates/demodulates computer signals, which are digital, into analog signals that can be transmitted over telecommunication lines, e.g. telephone. Modems are special purpose codec devices.
monitor profile: See color profile.
monochrome: Having one or more tones of a single color.
mosaic: A single image composed of numerous photographs arranged in multiple rows and multiple columns. Compare to panorama.

nodal point: The optical center of a lens. Which is not the same as the physical center of a lens.
noise: Any undesired interference with the conversion of light (an analog signal) to a digital capture (a digital signal) that causes a visible disruption to the integrity of the image. The capture can be via digital camera or the scanning of film or print. Digital photography noise is manifested as missing, incomplete or extraneous pixel data and falls into two categories: luminosity (tone) noise and chromatic (color) noise. Luminosity noise gives the image a grainy appearance in continuous toned areas, such as the sky. Chromatic noise appears as small colored speckles or spots in shadow areas. Compare to artifact.
non-destructive: Computer based image editing techniques that change an image's appearance without permanently altering the image's pixels.

outgas: Gases released by printer ink solvents.
outgassing: The act of printer ink solvents releasing gases as the ink cures.
output file: A general term used to describe an image file that has been prepared for print or display by being flattened, corrected for out of gamut colors, cropped and resized. Compare to scan file and master file.
out of gamut: A color that cannot be reproduced accurately by the device processing the image file.

parallax: The apparent shift in position of one object to another when seen from different points of view. The difference in the angle of view between one line of sight and another. For example, what the right eye sees is slightly different than what the left eye sees. This difference is called parallax. In a range finder camera, the difference between what is seen in the viewfinder and what is actually recorded on film is parallax. Parallax will be more pronounced the closer objects are.
panorama: A single image composed of multiple photographs arranged in a single row or a single column. Compare to mosaic.
pattern: The repetition of lines, shapes, forms or colors.
perceptual: A rendering intent used to convert out of gamut colors. If out of gamut colors are encountered, the Perceptual intent will shift both in gamut and out of gamut colors so as best to preserve the visual relationship between the colors while remapping out of gamut colors to a color that is in gamut in the destination color space. To learn more about the Perceptual rendering intent, read the Photoshop Color Settings page.
pincushion distortion: A lens aberration that causes straight lines in an image to bow inward, especially near the edges. Compare to barrel distortion.
pixel: An image pixel is the smallest, complete unit of color and tonal information about a single point in a digital image. For more information about image pixels, read the Pixels page. An image pixel is not the same as a computer bit, nor is it the same as a sensor pixel. For more information about sensor pixels, see demosaic.
posterization: The visible banding in an image due to the lack of smooth gradations between tones.
ppi: Pixels per inch. A means for denoting file resolution. For more about resolution, read the Resolution page.
print file: The image file that has been flattened, corrected for out of gamut colors, cropped and resized for printing. Compare to scan file and master file.
printer profile: See color profile.
profile: See color profile.
PSD: Photoshop Document. Adobe Photoshop's native file format. For more information about file formats, read the File Format page.

quantization: The process of compressing a wide range of values into a smaller range of numerical quantum values. For example, taking a picture with a digital camera converts light (an analog signal) to discrete units of data known as pixels. This conversion is a quantization process. Another example is file format conversion. The TIFF file format is capable of storing millions of colors. The GIF format can only store 256 colors. Therefore, when an image in the TIFF format is converted into GIF, it is processed by a quantization algorithm to convert all the colors in the TIFF image to no more than 256 color values.
QVGA: Quarter Video Graphics Array. A display standard used in the mobile device market. Also refers to a screen resolution of 320 pixels x 240 pixels. Has an aspect ratio of 4:3. It derives its name from the fact that its area is one fourth (a quarter) of the area of a VGA display.

raster image: The technical term for bitmap images.
Raw: Unprocessed data captured by a digital camera. Since Raw is a word and not an acronym, this web site spells it Raw, not RAW. To learn more about digital file formats, read the File Format page.
reciprocity: The relationship between shutter speed and f-stop that allows the same exposure to be achieved when one is changed to increase the amount of light and the other is changed to decrease light by the same amount. Therefore, shutter speed and f-stop are reciprocally related.
reciprocity failure: At extreme shutter speeds (extremely fast or slow) the reciprocal relationship between shutter speed and f-stop (see reciprocity) begins to break down and results in a loss of image quality.
relative colorimetric: A rendering intent used to convert out of gamut colors. For out of gamut colors, remaps the color to the closest in gamut color. Maps source white to destination white. To learn more about the Relative Colorimetric rendering intent, read the Photoshop Color Settings page.
rendering intent: The color space conversion option that determines how out of gamut colors are converted. To learn more about rendering intent, read the Photoshop Color Settings page.
resolution: A numeric value of how much information is being stored/can be created, per unit of measure. For example, 360 ppi. For more in depth information, read the Resolution page.
RGB: A tristimulus color model based on the properties of emitted light that stores color information as three color channels of red, green and blue. Red, green and blue are additive, or primary, colors. Light producing devices, such as computer monitors, projectors, TVs, etc, create millions of different colors simply by blending, or adding, various amounts of red, green and blue. The RGB color model determines what we see by controlling how the three colors of red, green and blue are mixed. Compare to CMYK.
RIP: Raster Image Processor/ing. Basically, there are two ways of printing an image: print drivers or a RIP. Either one will use a profile to interpret and render an image's colors and tones. However, print drivers come with the printer and RIPs are usually third party software packages that are purchased separately. RIP software bypasses the print driver and takes control of the printer directly. RIPs usually do a much better job of color management and printing. They also often come with additional features, such as batch printing and layout control.
RLE: Run Length Encoding. A lossless file compression method.
rubylith: 1. A distinctive, light ruby colored acetate film used for various masking purposes in graphics design and printing. 2. The default color used by Photoshop when in Quick Mask mode. This background color is rubylith.
rule of thirds: A guideline for where to place the subject in two dimensional art. Divide the media into three imaginary rows and three imaginary columns of equal height and width. There will be four points of intersection. Placing the subject on one of these four intersection points is the rule of thirds.

saturation: 1. Saturation is how pure hue is. The saturation 'range' goes from vivid to dull to grayscale (the absence of hue). A hue that is 100% saturated would be vivid. As hue is desaturated, it will become duller and if further desaturated, it will eventually become grayscale. In tristimulus color models, a color is desaturated by adding its opposite color. For example, to desaturate red, one would add cyan.

2. A rendering intent used to convert out of gamut colors. Converts the image's colors to highly saturated in gamut colors in the destination color space. This rendering intent should not be used where color accuracy is important. It should not be used for critical photography. To learn more about the Saturation rendering intent, read the Photoshop Color Settings page.
scale: A reference to size, distance or proportion created by including a known shape or form in the image. Depth is a particular scale referring to the perception of distance.
scan file: The digital capture of film or print. The first digital generation of film or print. The primary purpose of a scan file is to retain as much digital information as possible. Compare to master file and print file.
SD/SDHC card: Secure Digital/Secure Digital High Capacity memory card.
shape: The outline of an object. This is the characteristic of recognition. It is best shown using front or back light. It is two dimensional. A silhouette is a shape without texture or color.
signal to noise ratio: A digital image is a digital signal. Signal-to-noise ratio is the ratio of desired data to undesired data.
sidecar file: A XMP (Extensible Metadata Platform) file that contains the parameters for processing a Raw file.
soft proof: Soft proofing is previewing, on a monitor, how an image's colors (or shades of gray if a black and white image) will look when reproduced by another device, such as a printer. To soft proof in Photoshop, Photoshop must have access to the profile the targeted device will use to process the image. For more about soft proofing, read the Soft Proofing and Correcting Out of Gamut Colors page.
spectrophotometer: An instrument used to measure spectral reflectance (reflected light). Often used in the creation of scanner and printer profiles. Compare to colorimeter.
specular highlight: Light of such intensity and concentration, it is solid white with no color or texture and well past Zone X of the Zone System. Glare is a form of specular highlight.
spherical aberration: A blurred image caused by the way light passes through spherically shaped (rounded) optics. It is caused by the light at or near the center of the element coming into focus on a separate plane than the light near the edge of the spherical optic.
stitching: The process of combining multiple photographs into a single panoramic or mosaic.
stop, stop of light: A doubling or halving of light or the sensitivity to light. If the quantity of light is x and it is changed to 2x, then the quantity has doubled and has been changed by +1 stop. If the quantity of light is changed to ½x, then the quantity has been halved and has been changed by -1 stop. Example A, if a camera’s shutter speed is changed from 1/125 to 1/60, then exposure has been changed by +1 stop. Example B, if a lens’ aperture is changed from f/2.8 to f/5.6, then exposure has been changed by -1 stop. Example C, if the film in a camera has an ISO of 50 and it is replaced by a film whose ISO is 100, film speed has changed by +1 stop.
subject: The dominant visual design element or theme being photographed, or in a photograph. The center of interest. The subject is not necessarily an object. For example, the subject may be 'color' and the object may be tree leaves.

texture: The structural characteristics of a surface. It is the characteristic that affects the viewer's sense of touch. It is best shown using sidelight.
TIFF: Tagged Image File Format. A file format commonly used to store master and print files. For more information about file formats, read the File Format page.
tonal range: The digital tonal scale ranges from 0 to 255, for a maximum of 256 tones. Solid black has a digital tonal value of 0 and a Zone System value of 0. Solid white has a digital tonal value of 255 and a Zone System value of X. Mid tone has a digital tonal value of 127 or 128 (either can be used) and a Zone System value of V. For more information on the Zone System, read the Zone System page.
tone: The measurement (quantification) of an object's brightness/lightness. Same as luminance. For in depth information on tone, read the Tone page.
tristimulus color models: Any color model that uses numbers to describe color in terms of the three characteristics of 1-hue, 2-saturation or chroma, and 3-brightness, lightness or value.

UDMA card: Ultra Direct Memory Access memory card.

URL: Universal Resource Locator. The address syntax used by the Internet. It typically consists of the www prefix, a domain name, one or more folder names (optional) and a file name.

vanishing point: 1. The point in the distance where parallel lines, running from the viewer to the horizon, appear to converge. 2. In Adobe Photoshop's Photomerge perspective composition, it is the image that appears to be the furthest away.
vector graphic: A graphic file composed of mathematically defined curves and lines; referred to as vectors. Vector images are resolution independent because the image can be resized without losing detail since the data is stored mathematically, not as pixels. A good format for images composed of sharp lines and edges. Not a good format for storing gradual changes in tone. Compare to bitmap image.
VGA: Video Graphics Array. An outdated analog computer display standard. However, it is making a comeback in the mobile device and pocket PC markets. Also used to refer to a screen resolution of 640 pixels x 480 pixels. Has an aspect ratio of 4:3.
vignetting: The unwanted shading or darkening of the corners of an image. Usually caused by objects mounted on the front of the lens penetrating the lens' angle of view. Common causes are a mismatched lens hood or using too many filters on the lens.
visualization: The art of looking at a scene and using one's imagination to see the final image/print in one's mind and then using various photographic and darkroom techniques (both film and digital) to create the image.

white balance: A feature used to ensure white and other neutral colors are rendered as neutral in the image, thus removing any color casts. In film cameras, color correcting/compensating lens filters are used to remove color casts.

XMP: Extensible Metadata Platform. Non image file that contains Camera Raw adjustment instructions. It should not be confused with XML (Extensible Markup Language), which is a programming language used to describe the structure of data. Compare to EXIF.

yellow: A complementary color consisting of the primary colors red and green. This text is in yellow.

Zone System: A method developed by Ansel Adams (1902-1984) for determining exposure by analyzing tones and tonal range. For more information on the Zone System, read the Zone System page.