Digital Photography Glossary

The Digital Photography Glossary – This glossary will be updated periodically, so be sure to check back for new information.

Additive vs. Subtractive Color - Monitors project light to produce additive, or transmissive, colors, whereas printers use pigments or dyes to absorb light and create subtractive, or reflective, colors. Monitors use a combination of red, green and blue (RGB) pixels with twice as many green as red and blue pixels, whereas color printers use at least cyan, magenta, and yellow (CMY) inks. Most printers also include black ink (CMYK) because the CMY combination cannot produce deep shadows.

Bit Depth – Color bit depth is determined by how many different colors are available in an image color palette in terms of the number of computer “bits” (also known as O's and 1's) which are used to specify each color. Images with higher bit depths can display more shades of colors since there are more 0's and 1's available. With greyscale images, the bit depth is determined by how many unique shades of black, grey, and white are available. Most digital cameras produce color images that have 8-bits per channel. This allows for 256 different combinations—translating into 256 different intensity values for each red, green, and blue color. When all three primary colors are combined at each pixel, this allows for as many as 16,777,216 different colors. This is known as 24-bits since each pixel is composed of three separate 8-bit color channels.

Color Management – Color management refers to the process of ensuring that the best possible colors can be created in an image, starting with proper camera settings, to proper manipulation in computer software, to using the proper output adjustments depending upon whether the image is to be used on the web or to be printed, and selecting the proper printer settings and paper.

Color Space – Color space refers to the amount of colors and color variations in an image that can be displayed, whether on the web or in print. The most common color spaces are (in order of less colors to most colors) sRGB, Adobe RGB(1998), and ProPhoto RGB. Generally, the smaller sRGB color space is used for web applications, while the other wider color spaces are used in printing applications.

Compression Artifact – See “File Compression”

D.P.I. - DPI, or dots per inch, refer to the numbers of dots of ink sprayed per inch onto a digital printer. Generally, the higher the numbers of dots per inch, the better the color quality and detail in the print image. Do not confuse this with P.P.I., or pixels per inch, which refers to the resolution of the image file.

File Compression - Compressed files are significantly smaller than the original files and are in two general categories: "lossy" and "lossless." Lossless compression ensures that all image information is preserved, even if the file size is a bit larger as a result. Lossy compression, by contrast, can create file sizes that are significantly smaller, but achieves this by discarding color data, detail, and other image data so that lossy compressed files are not identical to the original. Visible differences between these compressed files and their originals are called "compression artifacts."

ICC Profiles – ICC profiles are used when accurate color renditions is desired when printing. Most high-end digital inkjet printing papers have their own ICC profiles which help communicate the proper color rendering from the computer to the printer by controlling the amount of ink.

JPEG - JPEG stands for "Joint Photographic Expert Group" and was developed for storing digital photographic files and has become the standard format for storing displaying photos on internet web pages. JPEG files are significantly smaller than TIFF files, however this smaller file size comes at a cost, since JPEG uses a lossy compression. Also, every time a JPEG is saved, it is further compressed.

Pixels - Pixel is a combination of the words "PICture ELement." Each pixel contains a series of numbers which create the colors. The precision to which the pixels can create colors is called the “bit depth” or color depth and, the more pixels the image contains, the more detail it has the ability to display.

P.P.I. - P.P.I., or pixels per inch, is a universal measurement that refers to how many pixels an image contains per inch of distance, whether horizontally or vertically. PPI does not vary no matter which digital device is being discussed because file resolution is not determined by the device. A megapixel is a million pixels and the number of megapixels determines the maximum print size that a camera can create, however, even if two cameras have the same number of pixels, that does not mean that the size of the pixels are equal. The major difference between an expensive DSLR and a compact point-and-shoot camera is that the DSLR has a much larger digital sensor area. So, even if both a DSLR and a point-and-shoot camera have the same number of pixels, the size of each pixel in the SLR camera will be much larger and a larger pixel has more of a light-gathering area, which means the light signal is stronger over a given interval of time and that creates a smoother and more detailed image.

Printing Settings: Relative Colorimetric vs. Perceptual Colorimetric – The relative colorimetric settings retains a near exact relationship between in gamut colors, even if this clips out of gamut colors. The perceptual colorimetric rendering also tries to preserve some relationship between out of gamut colors, even if this results in inaccuracies for in gamut colors. Perceptual maintains smooth color gradations throughout by compressing the entire tonal range, whereas relative colorimetric clips out of gamut colors. One other difference is that perceptual does not destroy any color information (it just redistributes it), while relative colorimetric does destroy color information. Color conversion using relative colorimetric intent is irreversible, while perceptual to colorimetric can be reversed. 

RAW - The RAW file format is similar to a negative in film photography as it contains untouched, "raw" pixel information straight from the digital camera sensor which has yet to undergo processing, and so contains just one red, green, or blue value at each pixel location. Many cameras have an option to create images as TIFF files, but these can use a lot more storage space. If your camera can create a RAW file format this is the best choice, since these files are considerably smaller and can retain even more information about your image.

TIFF - TIFF stands for "Tagged Image File Format" and is a standard in the printing and publishing industry. While TIFF files are considerably larger than JPEGs, they can be either uncompressed or compressed by using lossless compression which leaves all of the file quality intact. TIFF files can have a bit depth of either 16-bits per channel or 8-bits per channel, and can have multiple layers.