Frequently Used Terms

Bitmap - A specific file type, usually associated with artwork or photos that is made up of pixels. Examples are TIFF and PICT.

CMYK - A method of representing color based on the standard printing inks of cyan, magenta, yellow, and black. This is also known as 4-color process. Printing these colors on top of another will create a full color image.

Channel - There are two kinds of channels, color and alpha channels. Color channels are the fundamental building blocks of color images while alpha channels are created from selections.

Curve - A line graph that controls the ratio of input to output values for grayscale values in an image. A curve is often used to control the brightness and contrast of images and is used to adjust the distribution of grayscale values in individual color channels to accomplish color correction.

Dot Gain - The increase in the size of halftone dots that occurs when an image is printed. If not compensated for, dot gain often results in images that print too dark.

Dots Per Inch - A measure of the resolution of a screen image or printed page. Dots are also known as pixels. The typical screen display is 72 dpi, a laser printer can print at 300 dpi, and a plate setter can print at 2400 dpi or more.

EPS file - Encapsulated PostScript file. A picture file format supported by Adobe Systems and third party developers. It allows PostScript data to be stored and edited and is easy to transfer between Macs, PCs, and other systems. Will output only to PostScript devices.

Font Files - Files containing information used in the creation, display and printing of type characters. There are several font file architectures including PostScript and TrueType. PostScript font files are the preferred font files to use for PostScript printing.

Halftone - Because printing presses and laser printers cannot produce gray, the reproduction of a continuous tone image, such as a photograph, is processed through a screen that converts the image into dots of various sizes to provide the illusion of gray.

HSV - Hue, Saturation, and Value are used to describe the color of a pixel. Hue is the basic color determined by its frequency or wavelength of light. Saturation is controlled by the amount of white color added to the basic color. Value is the grayscale value or amount of black added to a pixel.

Image Resolution - The number of pixels per unit area in an image. Should be expressed as ppi (pixels per inch) and not dpi (dots per inch) which refers to output resolution.

Output Resolution - The dots per inch (dpi) of the output device.

PDF - Portable Document Format. A platform, OS, and application independent document format that allows for the viewing and printing of PostScript based documents without requiring the use of their native applications.

Pixel - Building block of a bitmap image.

Pixel Depth - The number of bits per pixel in an image. The pixel depth controls the number of shades of gray an image contains.

Preflight - The testing and preparation of a digital file before it is sent to print. Pre-flighting chores can be streamlined considerably by the use of a preflight utility. This is to be sure all elements are included such as fonts and images.

Raster Image Processor, or RIP - A device or program that translates the instructions for a page in a page description or graphics output language to the actual pattern of dots (bit map) supplied to a printing or display system.

RGB - Red, Green, Blue; a method of displaying color video by transmitting the three primary colors as three separate signals. Also, RGB refers to a method of specifying color by its component proportions of red, green, and blue. Files should be converted to CMYK to insure correct color for printing purposes.

Transparency - The fourth characteristic, in addition to HSV, used to define a pixel. The transparency of a pixel determines the amount of background that shows through that pixel.

Vector/Outline - A type of file, typically line art and logos, that is created out of lines and curves rather than dots. These files can be scaled without losing resolution. Vector images added to Photoshop images are rasterized or converted into pixels. If a Photoshop image (pixels) is enlarged, the resolution will be less and the image will not print as clearly.