Glossary of Common Digital Photography Terms
Anti-Aliasing Smooths out hard edges in a drawing by blending colors. This is especially apparent when applied to text.

 
Aperture Refers to the camera's adjustable opening (also known as a diaphragm or iris) that allows light to reach the camera's sensor (or film). The size of the aperture is measured using an f-number also called the f-stop (F8, f/8, etc). The smaller the f-number, the larger the camera's opening. The size of the aperture directly affects depth of field and shutter speed.

A low f-stop like F2 requires a higher shutter speed, which creates a shallow depth of field. A higher f-stop like F16 requires a slower shutter speed, which allows for a greater depth of field. Lenses usually have a minimum and maximum aperture. A lens with a large maximum aperture (or a low f-stop like F2) is often called a fast lens.
 

 
Artifact Unwanted distortions in an image caused by lossy image compression.

Artifacts like the ones on the left are typical of compressed JPEGs. The visibility of the artifacts depends on the level of compression used.

 
Bit The smallest unit of computer memory, short for binary digit. A bit has two states: zero (off) and one (on). Eight bits create a byte. Therefore, a byte can represent any one of 256 states (2 to the 8th power).

 
Bit Depth or
Color Depth		 The number of colors (or shades of gray) available in the image. Each pixel in an image is created by mixing the values for red, green, and blue. Currently, consumer-level graphics cards limit each color to one byte (or 8 bits) of memory. Consequently, the maximum color depth an image can have is 24 bits (3 x 8 bits for each color). These 24 bits allow for 2^24 (or 256 x 256 x 256) colors creating the rich 16.7 million color display you are used to. You can manually reduce this color depth for any individual photograph in an image editing software like FotoFinish. Reducing the bit depth reduces the number of colors displayed in the image. This smaller palette of indexed colors requires less memory to store than a regular 24-bit, or True Color, photograph. However, by reducing color depth, you also open the door to color banding and dithering.

 
Bitmap image Images created or captured as a grid of colored dots called pixels. Because a bitmap image - also known as a raster image - contains a finite number of pixels, the way a bitmap image looks is affected by its resolution. If you scale a bitmap image, it will lose detail and quality. See also vector image.

 
Blooming A distortion caused by an overflow of charge from one image sensor pixel to another. Blooming typically occurs with heavily backlit subjects such as leaves shot against the sky.

 
Blur A lack of sharpness in the image caused by resampling, a missed focus, or by camera or subject movement during a slow shutter speed.

 
Bracketing Taking two or three extra shots of the same subject with different exposure settings to ensure a perfect exposure.

 
Brightness Describes how light or dark we perceive a color to be. The higher the brightness value, the closer the color will be to white. The brightness of a color is the same as its value.

 
Burn To darken a small area of the picture in an image editing software or a darkroom.

 
Chroma Refers to the purity of color. The less gray, white, or black a color has in it, the more pure and vivid it will appear. Sometimes this term is used interchangeably with saturation.

 
Chromatic Aberration Purple fringing that occurs along the edges of backlit subjects such as plants, people, and buildings. Chromatic aberrations occur when the camera lens can't focus the different wavelengths of light onto the same spot on the image.

Notice the purple light along the edges of the bars on the picture to the right.

 
CMYK A color model based on four process colors: Cyan, Magenta, Yellow, and Black. The colors are mixed to create a full-color image on a printer. The printing press prints an image in four separate layers starting with yellow, then cyan, magenta, and black. The CMYK color model is different from the RGB model used on your computer display and digital cameras. Unlike a computer screen which emits light, ink absorbs it and the color our eyes perceive is the color that is reflected from the paper. Because the process involves absorbed instead of emitted light, CMYK is a subtractive color model (you start with white light and create colors by absorbing certain wavelengths of that light). Cyan absorbs the red component of white light, magenta absorbs green, and yellow absorbs blue. As you mix cyan, magenta, and yellow together, you will eventually get black.

 
Color or White Balance Refers to the relative intensity of colors in your image. Without correction, a picture taken at sunset can seem too yellow or orange and a picture taken under fluorescent lights might seem too green. Some cameras come with built in automatic white balance correction. You can also adjust the color balance in an image editing software. The colors are divided into three pairs: Cyan and Red; Magenta and Green; and Yellow and Blue. As you increase the amount of one color, you also automatically reduce its inverse.

 
Color Banding The appearance of visible bands of colors that replace subtle gradations in order to accommodate a reduced palette.

 

The original image
Colorbanding caused by reducing
the image to only 8 colors

 
Color Model A system of classifying individual colors. CMYK is the color model used in printing. RGB is the color model used in TV sets and computer monitors. HSL, HSB, HSV, and LCH are color models that describe how we perceive color.

 
Compression Storing image data in a way that results in a reduction in file size. Compressing data is especially important when you want to publish images to the web or e-mail. GIFs, JPEGs, and PNGs are all common compressed file formats. Compression can be lossy or lossless. Lossless compression doesn't lose any image data. GIFs and PNGs are lossless file formats (although GIFs lose color depth). Lossy compression results in the loss of image data every time the image is saved. JPEG is a lossy file format.

 
Contrast Measures the rate brightness values change in the image. A high contrast image has a narrow range of relative brightness values. As you increase contrast in an image editing software, the dark colors become darker and the light colors become lighter. For some images, increasing contrast can help bring out details in the image.

 
Depth of Field Refers to the distance between the closest and farthest sharp or in-focus portion of a photograph (also called the focal range). A large depth of field means that a large area both in front and behind your main subject will appear sharp. A shallow depth of field implies that anything other than your main focus point will appear blurred. A smaller f-stop (F2) will create a shallow depth of field. A larger f-stop (F11) will create a greater depth of field.

 

A picture taken with
the camera set to F8
A picture taken with
the camera set to F2

 
Digital Zoom A cropping and interpolation of an image within the camera to get closer to the main subject and mimic a greater zoom without actually gaining any additional image detail. Because it often results in a blurry and pixelated image, you should avoid using digital zoom.

 
Dithering The process of mixing existing colors to create the illusion of another color that is not available in the given palette. There are two types of dithering: pattern and diffusion. Pattern dithering arranges pixels in a rigid pattern. Diffusion dithering applies a random pattern of pixels that adds a subtle grainy texture to the image.

 
Dodge To lighten a small area of the picture in an image editing software or a darkroom.

 
DPI Short for dots per inch, DPI measures the resolution or density of dots within a given area. Originally DPI was used to describe printing resolution and PPI referred to the embedded resolution of a digital image, today many people use the two terms interchangeably.

 
Exposure The amount of light that your camera captures while taking a picture. Too much light can create an overexposed image while not enough light can result in an underexposed photograph. An overexposed photograph is lighter than it should be and an underexposed photograph is darker than it should be. Exposure is the result of any combination of aperture size and shutter speed.

 
Flare A series of bright polygons in the image caused by internal reflections within the camera's lens. Lens flare usually occurs when you shoot directly at a strong light source like the sun or a street lamp.

 
Gamut The range of colors that can be captured or displayed by a device.

 
GIF Stands for Graphics Interchange Format developed by Compuserve-Unisys. It is one of the main graphic formats displayed by web browsers. GIFs store bitmaps in patterns of indexed 8-bit color (256 colors or less) using a special algorithm called Lempel-Ziv-Welch (LZW). Using this algorithm, gifs compress the raw bitmaps into smaller file sizes. Because of their limited color depth, GIFs are better suited for images made up from solid colors such as logos, icons, and buttons.

 
Halftone The process (also called screening) by which a printer simulates continuous shades of colors while only using four colors: cyan, magenta, yellow, and black (CMYK). When printed, individual pixels in an image will be represented by a random pattern of these smaller, various-sized printer dots.

 
HSB A color model that describes color in terms of Hue, Saturation, and Brightness.

 
HSL A color model that describes color in terms of Hue, Saturation, and Lightness.

 
HSV A color model that describes color in terms of Hue, Saturation, and Value.

 
Hue The distinct characteristics of color that distinguishes blue from red and yellow from green, etc. Technically, hue is the dominant wavelength in the reflected or emitted light.

 
Interpolation An algorithm used to create pixels based on existing pixel data when you scale an image.

 
ISO (ASA) speed A measure of a film's sensitivity to light. A 400 speed film is more sensitive to light than a 100 speed film. Consequently, the faster film is better suited for low-light photography. Unfortunately, faster films also create more noise and reproduce colors less accurately than slower films. Digital cameras either have a preset ISO sensitivity or they allow you to choose from a variety of film speed settings.

 
Jaggies The stair-like appearance of diagonal lines.

 
JPEG Stands for Joint Photographic Experts Group. Along with GIFs, the JPEG file format is one of the main graphic formats displayed on the web. JPEGs use a compression method that sacrifices image information to reduce the file size called lossy compression. This means that every time you save an image as a JPEG, some of the original image data will be lost. JPEGs store images in 24-bit color (GIFs only use 8 bits or less) allowing you to save millions of colors. Consequently, JPEGs are better suited for photographs and images with fine gradations of tone and color.

 
LCH A color model that describes color in terms of Luminance, Chroma, and Hue.

 
Lightness See luminance.

 
Lossless compression A type of file compression that reduces file size without losing image date. PNGs and GIFs are common lossless file formats.

 
Lossy compression A type of file compression that results in the loss of image data every time the image is saved. JPEG is a lossy file format.

 
LPI Stands for lines per inch. LPI measures the frequency of lines a printer can create while halftoning.

 
Luminance The lightness or luminance of a color is similar to its value or brightness but the two are not the same thing. In the physical world, luminance is the physically quantifiable intensity of light measured in energy per unit area. On your computer the sun may appear brighter than a tree, but in reality each pixel on the screen is emitting the same amount of energy. Luminance is a way to recreate that light effect on the computer. Colors wash out as luminance increases and colors darken as luminance decreases.

 
Macro A one to one or higher magnification of a subject captured on film.

 
Noise An unwanted grain pattern in an image often caused by slow shutter speeds and high ISO settings.

 
Pan Moving the camera horizontally to capture a subject in motion.

 
Panorama A series of images stitched together to create a picture wider than what the camera is normally capable of capturing.

 
Pixel Short for a picture element, a pixel is the smallest unit of space in a computer image or display. Every image on your computer is made up of a colored grid of square pixels.

 
Pixelization The appearance of recognizable square pixels in an image. Pixelization usually occurs when a bitmap image has been enlarged beyond optimal range for its given number of pixels.

 
PNG Stands for Portable Network Graphic. The PNG file format is a great alternative to the GIF format. PNGs compress bitmaps without loss and also support transparency and 24-bit color. You can save a photo-quality image as a PNG without losing image information (like you would with a JPEG) or color (like you would with a GIF).

 
PPI Stands for pixels per inch. PPI is a way to measure resolution or the density of pixels within a given area. This measurement allows the software program to tell the printer how large to print a given image.

 
RGB An additive color model that starts with black, the absence of light. Computer monitors emit a combination of three colors: red, green, and blue to create a full color display. Unlike the subtractive CMYK model, with all three RGB colors combined, we get white light.

 
Resample Changing the pixel dimensions of a bitmap image. When you decrease the number of pixels in the image, you are downsampling, which results in a loss of image data and a blurrier image. Use downsampling to reduce the file size and viewing dimensions of an image for web or e-mail publishing. When you increase the number of pixels in the image, you are upsampling. Upsampling also often results in a blurry, pixelated image. You should avoid resampling images that are going to be printed.

 
Resolution Refers to the total number and density of pixels available in a bitmap image. Read this quick lesson for more detailed information.

 
Saturation The intensity of a color with respect to its brightness or value. Given a level of brightness, saturation measures the amount of gray in a color. A color that lacks gray impurities will seem more intense and vivid. Saturation is closely related to chroma.

 
Sepia A brownish colored, old-fashioned look to an image often created as a special effect either within a digital camera or in an image editing software.

 
Shutter Speed The length of time the image sensor is exposed to light anywhere from a few seconds (8s, 1s, etc.) to fractions of seconds (1/125, 1/500, etc.). You'll need a fast shutter speed to capture action. Slower shutter speeds (speeds below 1/125s) are more likely to create blurring from either camera shake or subject movement. The combination of shutter speed and aperture create a picture's exposure.

 
TIFF Stands for Tag Image File Format, a lossless cross-platform (both Windows and Macintosh) bitmap file format.

 
True Color A 24-bit color depth. See bit depth for more information.

 
TWAIN A standardized interface that allows software to communicate with scanners and digital cameras.

 
Value Describes how light or dark a color is. Value can be used interchangeably with the term brightness. A pale yellow color will seem lighter than dark blue. The higher the value of a color, the closer it will be to white and the lower the value the closer the color will be to black.

 
Vector image Images created using mathematical statements that define geometric shapes. You can move, resize, and change the color of vector graphics without losing any quality. Unlike bitmaps, vector graphics are not dependent on resolution. You can scale a vector graphic to any size and it won't lose detail or clarity.