The multimedia drivers VGAGRAY.DRV and VGAPAL.DRV, and the Windows driver VGA.DRV produce the high resolution of the MMV7VGA.DRV or MMWD480.DRV driver with a limited range of color or gray-scale. The advantages of these displays include small image files, relatively fast disk transfers, and use of a standard VGA display.
Images produced for a 16-color display might be incompatible with a gray-scale display; conversely, images produced for a gray-scale display might be incompatible with a 16-color display. If your images must appear on both 16-color and gray-scale displays, you might want to check your images for undesirable color or brightness shifts. The changeable palette of the VGAPAL.DRV lets you control the display of both 16-color and gray-scale images on a standard VGA display without the unanticipated color or brightness shifts. You can set the 16 changeable colors in the palette to shades of gray for a gray-scale display, or set it to the 16 colors you want.
With a 4-bit display driver, the system remaps 256 colors to the existing 16-color palette by default. This is the fastest way to display an 8-bit image on a 4-bit display. Unfortunately, the standard system colors don't usually provide enough color range to adequately display a 256-color image. Selecting the colors in the palette of the VGAPAL.DRV display driver can let you display many color images on a standard VGA display. While this driver limits the number of colors to 16, you can select the exact color shades you need to effectively display your images.
With a gray-scale display driver, the system remaps 256 colors to the gray-scale palette. Instead of attempting to match colors, GDI effectively matches brightness values from the 256-color image into the 16 levels of gray. This approach is as fast as remapping to 16 colors, as it uses the same method to display the image.
Remapping of 256-color images has some performance implications due to the additional time required to load an 8-bit image from disc (compared to a 4-bit image). You can improve performance at the expense of disc space by preparing two versions of images on disc—one in 256-color, and the other already mapped to standard system colors or gray scale. Applying a custom remapping algorithm (for example, one based on brightness for gray-scale) to your images lets you control the final appearance of your images. Remapping using a custom algorithm can also reduce the loss of information due to loss of color or color shifts.