GeoExpress - Knowledge Base Articles

A060403 - Adverse effects of transparency specification

Products:

GeoExpress 6 and earlier

Summary:

Specifying a separate RGB value for input transparency and output background may produce adverse color effects. The RGB or grayscale value specified in input transparency, if not replaced by valid image data, is replaced by the value specified for output background. When encoding indexed color images, specifying a separate RGB value for input transparency and output background may produce adverse color effects in the output image.

Cause:

Because indexed color images have such wide expanses of single color values, specifying any one of these color values as transparency and specifying an alternate color to act as a “nodata” background may cause valid image data to be replaced by the new background color.

Solution:

To avoid this color-replacement effect, particularly in indexed color images, specify the same RGB value for both input transparency and output background.

In later versions, GeoExpress disallows setting different values for transparency and background.

This article was last updated or verified on 18 October 2012.