[ Pobierz całość w formacie PDF ]
series will soon peter out... dialog via the context menu. Right click on the
image in the layers list and choose the Apply Layers
Mask. In the dialog which appears, select White (full
covering power). If you now paint in the image with
black as foreground colour and any painting tool,
the image becomes transparent at the Figure 6: X Files here we come...
68 LINUX MAGAZINE 11 · 2001
066gimpNewsbd.qxd 29.06.2001 20:17 Uhr Seite 69
WORKSHOP GIMP SOFTWARE
plug-in Semi-Flatten (/Filter/Colours/Semi-
Flatten) to some extent: This plug-in ensures that all
semi-transparent pixels (thus those which the GIF
format would ruin) are made non-transparent, by
counting them against the background colour. If
one has selected a colour here which matches the
average colour of the web page background, this
effect can be considerably weakened.
In Figure 9 the three different variants can be
seen. At top left there is a brushstroke with clean
anti-aliasing. In the middle this stroke has simply not
been converted into the GIF-type indexed format of
Gimp (colour chart with maximum of 256 colours).
The clean edge has given way to steps. On the right
below the brushstroke has been prepared, with the
Semi-Flatten plug-in, for a web page with a scarlet
background. Of course one should now only show
the image against a red background - otherwise it
looks very ugly. But against a red background one
can enjoy impeccable anti-aliasing.
Figure 7: With the curve dialog, you can increase the glow
Future prospects
In the next part we will make a foray into the Gimp
menus. We will look at a few gems among the
plugins and see how these can be combined to
make a few nice effects. %
Figure 9: Problems with the alpha channel in GIFs Figure 8: With the layer mask it is easy to release image elements
Alpha channel: refers to that part of a layer which contains information on transparency. The
alpha channel can be manipulated deliberately (with the curve tool) or protected (Retain
transparency in the layers dialog).
Release: is the name for the technique of separating a motif from the background. In our case the
tiger is separated from the landscape. The main motif can then later be inserted into other images.
GIF: is a file format which is very widely used on the WWW. Images saved in the GIF format can
define one (of the maximum 256) colours as transparent . This means a pixel can be either
transparent or again, not. Gimp s model of transparency goes further: A pixel can have one of 256
levels of transparency. Since the GIF format unfortunately has a few licensing problems (LZW
compression), you should avoid it as far as possible in your own web projects and instead use PNG or
similar. Unfortunately support for PNG is not yet available in every web browser.
%
11 · 2001 LINUX MAGAZINE 69
[ Pobierz całość w formacie PDF ]