Image Processing Reference
In-Depth Information
Creating a Sky Graphically — The Difference Clouds Filter
GIMP has a filter that lets you create clouds graphically. To use it, choose Filters
> Render > Clouds > Difference Clouds .
Try out the following.
Create a new layer in bluesky.xcf in the Layers dialog. Name the layer
cloudysky . Fill the layer with the color white with the help of the Bucket Fill tool .
Then open the Difference Clouds filter. The cloud structure is depicted in gray
in the preview window and will be colored later. You can experiment with the
slide controls to create the structure and density of the clouds. For our needs,
the default setting is good enough. Confirm the selection by clicking OK. The
cloudysky layer will be filled with a gray cloud structure.
Now from the Colors menu, select the Colorize function. Using the Hue
slider you can select the color tone of the clouds. By moving the Lightness
slider, you can determine how bright or dark the clouds should be, and with
Saturation, you can choose how intense your color should be. Depending on
the settings, you can create a stormy or sunny effect for your clouds.
The Colorize filter is also suitable for dying your black and white photos.
We'll go more into depth on this topic in section 4.4.1.
As the last step, you can compress your cloudysky image with the Scale
tool to get a perspective effect of a view from below. More on the use of the
Scale tool can be found in section 3.6.5.
When you select the Tilable check
box in the Solid Noise window of the
Difference Clouds filter, the edges of
the cloud structure will be created
(depending on the image size) so
that image can be merged together
like tiles. This is how you can create
seamless merged background
images for websites or patterns that
you can fill and paint with other
GIMP tools.
Figure 3.32
The options available in the Solid Noise window of the
Difference Clouds filter and the preview of the created gray-
scale image
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