4.15. Value Propagate

4.15.1. Overview

图 16.70. Example for the Value Propagate filter

Example for the Value Propagate filter

Original image

Example for the Value Propagate filter

Filter Value Propagate applied


This filter works on color borders. It spreads pixels that differ in a specified way from their neighbouring pixels.

4.15.2. Activating the filter

This filter is found in the image window menu under FiltersDistortsValue Propagate.

4.15.3. Options

图 16.71. Value propagate filter options

“Value propagate” filter options

Preview

The result of your settings will appear in the Preview without affecting the image until you click on OK.

Mode

The examples will be about the following image:

More white (larger value)

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

图 16.72. More white

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.

图 16.73. More black

More black

图 16.74. To bottom only

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.

图 16.75. Middle value to peaks

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.

Middle value to peaks

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.

图 16.76. Foreground to peaks

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.

图 16.77. Only foreground

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, More 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.

图 16.78. More opaque

More opaque

Original layer, with a transparent background.

More opaque

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


Propagate
Lower threshold, 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.

To left, To top, To right, To bottom

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.