The amount of pixels contained in the width and height of an image is referred to as an image’s dimensions. For instance, an image might be 320 pixels wide by 200 pixels high (commonly expressed as 320x200.) Image dimension is a key element of web design. Currently computers have a common group of fixed desktop dimensions ranging from 640x480 to 1280x1024 or higher. Web sites are usually designed “resolution-safe” meaning to the lowest com480 pixels high (640x480). Within the browser itself a width of 600 pixels is the common limit. This ensures that everyone viewing web sites with image capable browsers will be able to view your site.mon denominator, a desktop display at 640 pixels wide by 480 pixels high (640x480). Within the browser itself a width of 600 pixels is the common limit. This ensures that everyone viewing web sites with image capable browsers will be able to view your site.

Dimensions Dimensions in Browser 640 x 480 600 x 300 800 x 600 760 x 420 1024 x 768 955 x 600 1280 x 1024 1600 x 1200 Color Depth (Bit-Depth) Color depth describes the maximum amount of colors an image can contain. The number of colors an image contains is dependent on the image’s bit-depth. Confused? When users describe an image’s color depth, they might also describe it in terms of bit-depth.

The higher the bit value the more colors the image can contain.

Images are made up of one of four standard bit depths: 1 bit, 8-bit, 24-bit, and 32-bit. A 1-bit image consists of either black or white, or two colors. 8-bit images contain a maximum of 256 colors or 256 shades of gray.

24-bit images contain a maximum of 16.7 million colors. A 24-bit image is made up of three 8-bit channels, a Red channel (256 shades of Red), a Blue channel (256) shades of Blue), and a Green channel (256 shades of Green). 32-bit images would contain over a billion colors; however, the final 8 bits of the image are commonly reserved for alpha channel information rather than color. Alpha channels are covered later.

Bit-Depth Colors 1-bit 2 8-bit 256 24-bit 16.7 Million 32-bit 16.7 Million A 24-bit image consists of three (3) 8-bit channels (256 x 256 x 256), which make up a potential of 16.7 million colors.

Digital Image Types: Vectors and Bitmaps There are two digital image types: bitmaps and vectors. Bitmap images are the most common type of image file outside the professional print world. Bitmap files map out or plot the image on a pixel-by-pixel basis. Computer displays are made up of a collection of individual points or dots, called pixels, organized in columns and rows (similar to a table or a grid) where each cell represents each pixel in the image. The bitmap image file basically plots each pixel, such as pixel 300 wide by 250 high is red. Pixel 301 wide by 250 high is also red. Pixel 302 wide by 250 high is yellow and so on. Because bandwidth is a major concern when developing web sites, keeping the size of images to a minimum is very important.

The main benefit of bitmap images is photographic color, tone, and texture is accurately produced.

If you were to plot a bitmap on a grid, each pixel is detailed. Essentially, this is what your computer does when it displays bitmaps.