PUB3: Why Some Objects Dither with 256-Color Video

Q133173

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The information in this article applies to:

 - Microsoft Publisher for Windows 95, version 3.0
 - Microsoft Publisher 97
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SUMMARY
=======

If you run Publisher while your display is configured for 256 colors, many
different objects will appear dithered. If you open the same publication
when your display is configured for 32,000 or more colors, the same objects
display without dithering.

Dithering is the process of simulating one color by breaking it up into a
pattern of dots of different colors.

These types of objects may dither when displayed at a color depth of 256
colors:

 - Imported graphics
 - OLE objects
 - Recolored pictures
 - Publisher drawing objects filled with tints, shades, or gradients

These types of objects will not dither when displayed at a color depth of
256 colors:

 - Text
 - Single-pixel thick lines
 - Publisher drawing objects filled with any color in the Colors dialog box
   with the Basic Colors button selected

MORE INFORMATION
================

Many Windows 95 programs have a fixed palette of 256 nondithering colors to
use when Windows 95 is running with a display configured for 256 colors.
Publisher is one of these.

When Publisher renders an object to the display driver, it determines
whether the video driver should display that object using one of the colors
on the palette or using the best approximation of the actual color through
dithering.

The objects that Publisher does not dither are those objects that become
hard to use if they are dithered. Dithered text, for example, is often very
difficult to read.

The types of objects that Publisher allows to dither are those objects that
suffer visually if their colors are changed too much--for example, if you
have an object that has a gradient fill from light-blue to black. The
standard 256 color palette may only have two or three shades between light
blue and black, which is not enough to display a nice gradient. In this
case, a dithered gradient gives a better approximation of what the object
will look like when you print it.

For the same reason, it would be difficult to tell the difference between a
tint of 10-percent yellow and a tint of 2-percent yellow using the standard
palette. Dithering these tints makes it possible to visually identify and
compare objects filled with these colors.

If you change your Windows 95 display settings to a color depth of High
Color 15-bit (32,768 colors), High Color 16-bit (65,536 colors), or True
Color (16,777,216 colors), Publisher won't use its palette, and no objects
will dither.

You cannot modify the algorithm Publisher uses to decide which object to
dither and which to display as pure colors.

Additional query words: 3.00 dots stripes x's patterns halftone spots
spotted dotted band banded