The Edit Alpha Channel command can be used to manually edit a 32-bit picture's alpha channel. The alpha channel will be opened in a separated window for editing. Any of PixelNEO's tools, special effects, etc. may be used to make changes to the alpha channel.


An alpha channel is a special mask used to identify which portions of a picture should be transparent (see through) and which portions should be opaque (solid). In addition to completely transparent or completely opaque, an alpha channel can also include partial transparency.


An alpha channel is essentially a grayscale mask containing up to 256 shades of grey. Each pixel in the mask represents a transparency level for the corresponding pixel in the original picture. A mask pixel with a value of zero (black) means the corresponding picture pixel is 100% transparent. A mask pixel with a value of 255 (white) means the corresponding picture pixel is 100% opaque. A mask pixel with a value of 128 (medium grey) means the corresponding picture pixel is 50% transparent.



The illustration below shows a typical 32-bit picture and its alpha channel mask:


The original picture (left) and its alpha channel.

The black portions of the alpha channel are 100% transparent and the white portions are 100% opaque. However, if you zoomed in on the alpha channel, you would see that the edges of the leaf image, which appear to be only black and white, actually include a very subtle transition with lots of grey shades. This translates into a subtle transparency along the edges of the leaf. The importance of this becomes clear when we superimpose the leaf picture on top of complex background. The alpha channel allows the edges of the leaf to blend seamlessly with the background using an anti-aliased effect, which results in a picture that appears smooth and crisp.


This feature is only available when editing 32-bit pictures.