Device-Independent/Device-Dependent Bitmaps

A bitmap image, also called a raster image, is an image held in the form of successive rows (called rasters) of pixel data. As already stated, ImageGear's bitmap images use 1, 4, 8, or 24 bits to represent each pixel. But besides these pixel bits, additional information is necessary to describe an image. For example, the width (number of pixels per row) and height (number of rows in the image), are required. For some images, a color palette may be required. Depending upon how the bitmap is to be used, additional information may be required or useful.

To hold bitmap images in memory, ImageGear uses two types of bitmaps, both widely used by many other software products and supported by development platforms such as Microsoft Windows. These are the Device-Independent Bitmap (DIB) and the Device-Dependent Bitmap (DDB). The DIB is by far the more widely used for in-memory operations. It has become the common denominator format because it is so simple: it describes just the image, without reference to characteristics of the device(s) upon which it may later be displayed. While ImageGear provides convenient ways to convert between DIBs and DDBs and to display DDBs, nearly all ImageGear operations are performed on DIBs exclusively.