I am working with an image with an alpha channel, and I am noticing some brushes work with the alpha channel (the channel blocks out the pas in that area) and some brushes cover the whole area, regardless of the alpha channel.
How do I modify a brush to recognize an alpha channel?
For instance, the brush acycle swirl works with the alpha channel, but the brush abstract 2 does not. Why is that? Can I modify the brush to recognize an alpha channel?
I hope I am explaining this right...
Thanks, SA is a beast with a ton to learn!
Replies
In the Brush Type control panel, the setting of the Brush Type parameter determines whether the alpha channel associated with an image or movie brush is used or not. If Brush Type is set to Source Brush, then the RGB channels of the brush are used for the brush shape. If the Brush Type is set to Source Alpha Brush, then the alpha channel of the source brush is used for the brush shape.
By brush shape, i mean the brush image that defines the Fill From - Fill To mix. Fill From and Fill To being specified in the Paint Fill Setup control panel.
If you are using a 'region fill as brush' pen mode paint preset, then there is an additional setting you need to be aware of. In addition to the Source Alpha Setting mentioned above, you'd also need to set the Brush Option to Alpha Only in the region as Brush Mode control panel. Region Fill as Brush pen mode derives a temporary region that overrides the brush source to define a paint nib. By using alpha only for the Brush Option, then you can still use whatever image or movie brush RGB values are loaded in the Brush Source control panel, and use the temporary generated region shape to just override the Brush Source alpha channel.
thank you! this has helped immensely.
The other thing to be aware of is that luminance = 255 in a brush image will act as a mask (so full on white). So if you had a sphere on a white 255 background, the white background would be acting like a full off alpha channel for masking purposes with a normal Source Brush Type. And with a normal Source Brush Type, a brush value of 254 will be mixed fully to the Fill To signal, and a brush value of 0 will be fully mixed to the Fill From signal, and anything in between will be a smooth transition ( if you are using the Blend algorithm for the Fill Option parameter in the Paint Fill Setup control panel ).