I

Image File Format : A representation (usually binary) used by a computer system as an agreed format to store an image. Examples of image file formats include the Graphics Interchange Format (GIF) and Tagged Image File Format (TIFF).

Inbetweening : Inbetweening is the generation of intermediate transition positions from a given start and end point or keyframes. This technique is often used in animation, where a lead artist generates the beginning and end keyframes of a sequence (typically 1 second apart), a breakdown artist does the breakdowns (typically 4 frames apart), and an ‘inbetweener' completes the rest.
Indexed Color : In PhotoShop, an image mode in which there is only one channel and a color table that can contain up to 256 colors. All the colors in an Indexed Color image are displayed on its table.
Indexed 16 and 256 Color Images : An indexed color image consists of a set of references to values stored in a color table or palette. The palette, which is often contiguous in an image file, lists all the colors as sets of coordinates in color space. An indexed 16-color image contains a palette with 16 color entries (4 bits), whereas in an indexed 256 color image 256 colors are listed (8 bits).

Interpolation : A process that occurs automatically when an image's dimensions or resolution are changed which results in re-coloring the pixels. Interpolation may cause an image to look blurry when it's printed. You can choose an interpolation method in PhotoShop from slower, but better, to faster but lower quality.
Interlaced Display : A technique for displaying images at a higher resolution than the monitor. Two images consisting of every second row of pixels are alternately displayed during every screen refresh (e.g. every fiftieth of a second). There is hence a flickering artifact.

Inverse Kinematics (IK) : The study of how movement of a body part affects other attached body parts.
Invert : To reverse an image's light and dark values and/or colors.