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16.117 - Sample Alpha

Quick Reference to Scripting Command
a=SAMPLEA(MODE[0-2]) (result is SAMPLE)
Items in CAPS are 0/1 or ranges with more options than just 0/1.
Ranges other than 0/1 are indicated by brackets, such as [0-2].

Sample Alpha returns the alpha level for the region selected. You can use the returned value to adjust the alpha channel, using the Make Alpha operator.

16.117.1 - Alpha Action Summary

Alpha channel transparency is 100% and opacity 0% when an alpha channel value is 0.

Alpha channel transparency is 0% and opacity is 100% when an alpha channel value is 255.

Transparency and opacity vary linearly between 0% and 100% depending on the alpha value present for each pixel in an image.


If you're experiencing trouble displaying alpha for an image, you might need to use the Change Image Info command in the Window menu. This will allow you to turn on the "Has Alpha" flag for any image. Image types such as JPEG do not have alpha, and so images of this file type, and similar "alpha-challenged" file types, will not have this flag on. Some operators (e.g. Make Alpha) turn this flag on automatically, but there are conditions where the flag is not set as you desire and this dialog can allow you to easily remedy that situation.

Operator Dialog

16.117.2 - Sample Alpha Controls - Level

This is the level determined by the operation. Once taken, this level is also made available to the Make Alpha operator, via the <--Sample Alpha" button in that operator's control dialog. - Method

You may choose the bulletsel.png Average , bulletsel.png Minimum  or bulletsel.png Maximum  of the alpha levels collected from within the region of your area selection.

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