This filter works on color borders. It spreads pixels that differ in a specified way from their neighbouring pixels.
The result of your settings will appear in the Preview without affecting the image until you click on
.The examples will be about the following image:
Pixels will be propagated from upper value pixels towards lower value pixels. So bright areas will enlarge.
Pixels will be propagated from lower value pixels towards upper value pixels. So dark areas will enlarge.
On a border between the selected thresholds, the average of both values is propagated.
The propagated areas will be filled with the foreground color of the toolbox.
Only areas with the Toolbox Foreground color will propagate.
Only areas with the Background color will propagate.
These commands work like “More white” and “More black”. Opaque (transparent) areas will be propagated over less opaque (transparent) areas. These commands need an image with an alpha channel.
A pixel will be propagated (spread) if the difference in value between the pixel and its neighbour is no smaller than the lower threshold and no larger than the upper threshold.
That's the propagating amount. The higher it will be the more colored the propagation will be.
You can select one or more directions.
If checked, the pixel alpha value will be propagated, otherwise the pixel will get the alpha of the neighbouring pixels. This checkbox is only visible when the active layer has an alpha channel.
If checked, the pixel's color channels (gray channel on grayscaled images) will be propagated. The option is checked by default, of course. This checkbox too is only visible when the active layer has an alpha channel.