Types of Digital Image Files

A digital image is composed of a finite number of elements called pixels, each of which has a particular location and value (intensity). Typically, pixels are organized in an ordered 2-dimentional array (Matrix). The size of an image is determined by the dimensions of this pixel array. The image width and height are the number of columns and the number of rows in the array respectively. Thus, the pixel array is a matrix of M columns x N rows. To refer to a specific pixel within the image matrix, we define its coordinate at x and y positions.

Each pixel has its own intensity value, or brightness. If all the pixels have the same value, the image will be a uniform shade i.e. all black, white, gray, or some other shade. It is in the type of intensity used for each pixel that image types vary from one another. Black and white images only have intensity of the black and white. Grayscale images have intensity from the darkest gray (black) to lightest gray (white). Color images, on the other hand, have intensity from the darkest and lightest of three different colors, Red, Green, and Blue. The various mixtures of these color intensities produce a color image.

Intensity values in digital images are defined by bits. A bit is binary and only has two possible values, 0 or 1. An 8-bit intensity range has 256 possible values, 0 to 255.

Two most basic types of digital images are:

• Black & White
• Grayscale
• Red-Green-Blue.

TIFF (also known as TIF), file types ending in.tif

TIFF stands for Tagged Image File Format. TIFF images create very large file sizes. TIFF images are uncompressed and thus contain a lot of detailed image data. TIFFs are also extremely flexible in terms of color and content.

JPEG (also known as JPG), file types ending in.jpg

JPEG stands for Joint Photographic Experts Group, which created this standard for this type of image formatting. JPEG files are images that have been compressed to store a lot of information in a small-size file. Most digital cameras store photos in JPEG format, because then you can take more photos on one camera card than you can with other formats.

GIF, file types ending in.gif

GIF stands for Graphic Interchange Format. This format compresses images but, as different from JPEG, the compression is lossless (no detail is lost in the compression, but the file can’t be made as small as a JPEG).

PNG, file types ending in.png

PNG stands for Portable Network Graphics. It was created as an open format to replace GIF, because the patent for GIF was owned by one company and nobody else wanted to pay licensing fees. It also allows for a full range of colour and better compression.

Raw image files

Raw image files contain data from a digital camera (usually). The files are called raw because they haven’t been processed and therefore can’t be edited or printed yet. There are a lot of different raw formats–each camera company often has its own proprietary format.