Hi Max,
PixInsight fully supports pixel transparency via
alpha channels. Alpha channels are additional channels besides the nominal channels of an image; for example a fourth channel in a RGB color image, or a second channel in a grayscale image.
In PixInsight, the first alpha channel is what we call the
active alpha channel, and it defines the
opacity of an image. When a pixel in the active alpha channel is white, the corresponding image pixel is opaque. When the alpha value is black, the image pixel is completely transparent. Intermediate (gray) alpha values define proportional opacity values.
When an image has at least an alpha channel, you may decide whether to represent it as a transparent image or not, and how transparency is rendered on the screen. The options you have mentioned control these functions:
- Show Transparency toggles between showing transparent images as such, or as normal images (ignoring the active alpha channel).
- Background Brush. If this option is selected, transparent images are rendered over a canvas filled with a special transparency brush, which you can define with Preferences (Transparency section, under Colors and Fonts -- but, please be careful because there is a bug in PI 1.5.2 that can cause a crash if you change these settings; this bug is fixed in the next version).
- White Background / Black Background. If one of these options are selected, transparent pixels are rendered over a canvas filled with the corresponding opaque color.
- Default Color. This is similar to white/black background, but you can define a canvas color with Preferences.
Here is an example of a transparent image loaded in PixInsight:
http://forum-images.pixinsight.com/legacy/1.5.5-preview/Transparency.jpgThe CreateAlphaChannels and ExtractAlphaChannels standard processes (Image category) allow you to manage alpha channels.
