Multi-Monitor Color Rendering on Displays with Different Color Depths (281495)

MORE INFORMATION

The behavior that is described in this article is a limitation of how display palettes can be realized across multiple displays.

A palette is a set of index values that identify the colors that can currently be drawn on a display that is capable of generating more colors than can be simultaneously shown. A display driver specifies its palette so the Windows Graphics Device Interface (GDI) can determine how different color indexes are to appear on the device. High and True color display settings are not generally palletized, but a 256 color display setting is.

Colors that are not solid on a 256-color display are those whose red green blue (RGB) values are not evenly divisible by 8. For example, the Desktop (background) color in the Windows Me Windows Standard scheme is RGB=58,110,165, which is not solid in the 256-color palette.

The operating system retains control of 20 colors, to provide VGA color functionality to programs that do not use palettes. The remaining 236 colors are available for general program use. A desktop scheme can yield dithered colors for some items when it is not possible to reconcile a non-solid color to the reserved colors on both displays.

For additional documentation about palette management, please view the "References" section of this article.

Note that if there is only one display and a non-solid color is selected, the Windows 95, Windows 98, and Windows 98 Second Edition desktop will dither the color, but Windows Me will not. Microsoft Windows 2000 has enhanced palette management that normalizes color mappings so that they remain solid on multiple displays.

The following tables list in detail how multiple displays can react to non-solid 256 color selections. In addition to dithering, the Appearance tab may render colors improperly under the following circumstances:

• The color scheme preview window and the color control may incorrectly show a color item as dithered.
• The color control may render the wrong color when the tool is dragged from display to display.
• Quitting and then restarting the Display tool fully reinitializes the Display tool, and can reduce any preview or display conflicts.

Legend:

   Display Color Settings (Primary and Secondary display):
      Colors  - the Settings tab Color control selection
   Value Headings:
      Desktop - the Appearance tab Item control 'Desktop' selection
      Preview - the sample desktop on the Appearance tab
      Color   - the Appearance tab Color control selection
   Heading (suffixes):
      Pri     - the primary display (display 1)
      2nd     - the secondary display (display 2, and so on...)
   Values
      D = Dithered
      S = Solid
      E = Error (wrong color when tool is dragged to another display)
				

Windows Me

Colors(Pri)	Colors(2nd)	Desktop(Pri)	Desktop(2nd)	Preview(Pri)	Preview(2nd)	Color(Pri)	Color(2nd)
256	256	S	S	D	D	D	D
256	High/True	S	S	D	D	D	S
High/True	256	S	D	S	S	S	D, E
High/True	High/True	S	S	S	S	S	S

Windows 98, Windows 98 Second Edition

Colors(Pri)	Colors(2nd)	Desktop(Pri)	Desktop(2nd)	Preview(Pri)	Preview(2nd)	Color(Pri)	Color(2nd)
256	256	D	D	S, E	S, E	D	D
256	High/True	D	S	D	D	D	S
High/True	256	S	D	S	S, E	S	D
High/True	High/True	S	S	S	S	S	S

Note that this behavior can be easily demonstrated on a Windows Me-based computer that is using the Windows Standard scheme. The Windows Standard scheme includes colors that are not solid on a 256 color display.