Adobe PhotoShop 6.0
Image Types

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Overview

There are two main types of computer images: vector images and raster (or bitmap) images. Photoshop deals only with raster images. Adobe Illustrator is an example of an imaging tool that creates vector images.

Raster images are stored in the computer in the form of pixels: tiny squares on a grid. Unless one zooms in on an image, those tiny squares may be hard to see. Variations in the colors of the pixels produce areas of colors in the picture. Resizing raster images can be problematic, because as you stretch the picture out, the "pixellated", or gridlike, effect becomes much more obvious.

The "grid" of a raster image

Vector images are stored in the computer as mathematically defined lines, curves and shapes. Shapes and lines (called "paths") are colored to create a picture. Vector images remain clear no matter what size they are scaled to, because the equations for the lines can easily be recalculated at new sizes.

The "paths" of a vector image

Photoshop uses a proprietary type of file (the Photoshop Document, or .psd) to store information important to further editing in Photoshop (such as layers and text information). But Photoshop also supports a variety of other file formats including bitmaps (.bmp) CompuServe GIFs (.gif), PICTs (.pct), TIFFs (.tif), and JPEGs (.jpg). These are all raster image types.

Raster (Bitmap) Graphics

• Use a grid of small squares known as pixels to represent images.
  
  
• Resolution-dependent: contains a fixed number of pixels,can lose detail and appear jagged when magnified, enlarged, or printed at too low a resolution.
  
  
• Can show gradations of color, detailed images such as photographs well.
  
  
• Generally larger file size, especially with larger, higher-resolution pictures.

Vector Graphics

• Consist of outlines and fills.
  
  
• Resolution-independent: can be scaled to any size and printed on any output device at any resolution without losing its detail or clarity.
  
  
• Best choice for type and bold graphics that must retain crisp lines when scaled to various sizes.
  
  
• Generally smaller file size

Examples

Which image type is more appropriate for the picture?

Additional information about JPEGS and GIFs