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Another cool set of
effects can be found in DoggFXs "Other FX" collection. For example, the
White Noise effect creates something that looks like TV snow.
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When applying some of
these effects filters, you may find an optional checkbox to use the
Alpha channel.
Let's take a look at how to create such a selection or mask in the
alpha channel.
< click for
fullscreen view
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In the main Tools panel
you can find several tools that can be used to create a selection:
Lasso, rectangular, oval or magic wand tools, they all are part of the
'Alpha' tools. Right-click them for more options. Left cick to
activate.
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For example, using the
Oval (circle) Alpha tool, we can click and drag from about the center
of the image to the outisde and create an oval selection. The marching
ants show the curent selection.
You can use the Shift key while working with these alpha tools in order
to add to the current selection. When drawing the selection with the
left button, it will then add to the current selection. When drawing
with the right button, it will remove from the current selection.
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It is a good idea to
occasionally take a snashot of the alpha channel, work in progress,
especially if you're creating very complex masks.
Use the menu:
Alpha>Store alpha...
to grab a snapshot.
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The Alpha menu aso has a
Transform option. This can be used to reposition the mask, or scale and
rotate it.
< click for
full view
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Here we used the Transform Apha to re-center the seection and slightly
increase the size.
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You may aso want to blur
the Alpha a little, so that the selection is not a sudden switch from
fully enabled pixel to fully disabled. A gradual ransition is ften
preferable.
Alpha>Blur alpha...
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Set the amount of
blurring. Click OK.
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Two stored alpha images:
lower left is showingthe original, with a crisp and sudden transition
from black to white. The upper-right version shows a blur effect on the
alpha was applied. There is a gradual transtion through greyscale
values.
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The dashed lines on the
marching ants display may not look much different after blurring the
alpha. That's because the dashed lines show where the level is at
50% - between fully selected and fully non-selected. Blurring
that doesn't change much about where the 50% level is - it typically is
still at the same place. But instead of transitioning there from fully
enabled to fully disabled, or from opaque to transarent, or from white
to black if seen as a greyscale, you will expect to see a grey gradient
around that line. Be sure to Store the alpha again, or click "Get
Alpha" in the currently stored view of the earlier alpha image.
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The current selection is
on the inside of the oval zone. We would like to use the outer part.
Simply Invert the alpha from the Alpha menu, or click 'Invert' on the
stored version, followed by 'Replace'.
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With the alpha channel now
in place and ready to go, use the DoggyFX tool with 'Use Alpha?'
selected.
Notice also that in this case you could limit the scope of the effect
to some of the frames instead of it affecting the entire clip. By
default however, all framesare selected. This clip has 120 frames, so
it starts at frame 0 and goes through frame 119.
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And here it is.
Below is a version converted to a Flash stream after saving it as an
AVI.
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