Image Storage Bitmapped Graphics – in which an image is represented as a collection of dots Vector Graphics – in which an image is represented as a set of instructions telling the computer how to draw the image.

Bitmapped Graphics

Vector Graphics

Color Depth Color Depth – the number of colors that an image could contain. Eight bits (one byte)– allow 256 colors. Two bytes – allows colors. 24 bit color gives one byte to each of the three primary colors thus allowing 256 intensity levels for each of red, green and blue. 32 bit color allows 16 million different colors although typically few displays are capable of showing that many colors.

Color Representations Subtractive Colors – red, yellow, blue are primary colors for pigments. Additive Colors – red, green, blue are primary colors for light. Since computer screens use light, additive colors are used for images on computers.

Compression When an image is compressed, there is a potential loss of quality. If quality is not lost then the compression is called lossless. If quality is lost then the compression is called lossy.

Lossy Compression formats JPEG (joint photographic experts group) (.jpg or.jpeg) typically used for photographic images. Color depth of 24 or 32 bits is common. GIF (graphics interchange format) (.gif) typically used for drawings. The color depth is only 8 bits so 256 colors are all that are available. However, these can be drawn from many different pallets, so depending on the colors used the image could be realistic. Both JPEG and GIF are web standards, which means that all browsers can render images in these formats.

Lossless formats. Typically used when the highest quality must be retained. PNG (portable network graphics) is also a format suitable for photorealistic images. It is a web standard. Typically the image size will be larger than jpeg. BMP (microsoft bitmapped image) TIFF (adobe tagged image file format)