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Pixel Storage

The Macintosh pixel storage format is big-endian. This format has the following general characteristics:

• All the bits that define any single pixel on the screen (ranging from 1 to 32 bits) are adjacent in memory.
• The bit groups that define each pixel are successive and contiguous in memory, starting with the pixel at the upper-left corner of the screen and ending with the pixel in the lower-right corner of the screen.

For example, a frame buffer that defines a screen 640 pixels wide by 480 pixels high (307,200 pixels), using 1 bit per pixel, contains 38,400 bytes. The most significant bit of the first byte corresponds to pixel 0, located in the upper-left corner of the screen. The least significant bit of the last byte corresponds to pixel 307199. This example is diagrammed in Figure 2-3.

Figure 2-3 Sample frame buffer format

If the same frame buffer had a color depth of 8 bits (thereby containing 307,200 bytes), all of the first byte would be used to store information about pixel 0 and all of the last byte would be used to store information about pixel 307199.

For further information about Macintosh pixel formats, see Graphic Memory Formats