The examples will be about the following image (zoom x8):

More white (larger value)

Pixels will be propagated from upper value pixels towards lower value pixels. So bright areas will enlarge.

Figure 16.72.  More white

Bright pixels have been propagated to dark pixels in the four directions : top, bottom, right and left. Filter applied several times to increase effect.

More black (smaller value)

Pixels will be propagated from lower value pixels towards upper value pixels. So dark areas will enlarge.

Figure 16.73.  More black

Figure 16.74.  To bottom only

The same as above with To bottom direction only checked.

Middle value to peaks

On a border between the selected thresholds, the average of both values is propagated.

Figure 16.75.  Middle value to peaks

A thin border with a transitional color has been added to objects. It is not visible around objects with smoothed borders.

Green area zoomed x800. A thin border (one pixel wide) has been added. Its value is the average between grey (90%) and green (78%) : (90 + 78) / 2 = 84.

Foreground to peaks

The propagated areas will be filled with the foreground color of the toolbox.

Figure 16.76.  Foreground to peaks

In this example, the foreground color in Toolbox is Red. A thin border, one pixel wide, red, is added around objects. With smoothed objects, this border is located at the furthest limit of smoothing. Here, another border appears inside. This is an artifact due to the small size of the object which makes the smoothing area of opposite sides to overlap.

Only foreground

Only areas with the Toolbox Foreground color will propagate.

Figure 16.77.  Only foreground

In this example, the foreground color in Toolbox is that of the green object. After applying filter several times, the green area is clearly enlarged.

Only background

Only areas with the Background color will propagate.

More opaque / transparent

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.

Figure 16.78.  More opaque

Original layer, with a transparent background.

Filter applied several times: the green, opaque, area got increased.

Lower / Upper threshold

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.

Propagating rate

That's the propagating amount. The higher it will be the more colored the propagation will be.

Propagating direction

You can select one or more directions.

Propagating alpha channel

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.

Propagating value 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.