4.15. Value Propagate
| 4. 扭曲滤镜 |

### 4.15. Value Propagate

#### 4.15.1. Overview

图 17.71. Example for the Value Propagate filter

Original image

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 Filters → Distorts → Value Propagate.

#### 4.15.3. Options

图 17.72. “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 17.73. 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 17.74. More black

    图 17.75. 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 17.76. 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.

    图 17.77. 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 17.78. 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 17.79. More opaque

    Original layer, with a transparent background.

    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.

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