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Convert Red channel into Alpha

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Hello, i've got a image, it contains a red channel only, i would like the red channel in this image to be a alpha channel, the darker the red the more alpha, i.e. 255 red, 255 alpha. 0 red, 0 alpha, i've tried blending but i cant seem to get the right result, is there a way to convert a single channel?

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The simpliest way is to use Curves+ plugin.

Choose Advanced mode, in: Red, out: Alpha.

Default curve shape (straight line from bottom left to top right) represents 1:1 conversion from red to alpha as you described (R255->A255). You may want to bend the curve to adjust the effect. Reversed curve (top left to bottom right) converts in opposite direction (R255->A0).

Color to Alpha plugin may be too difficult to set up for that task. Thanks for publicity, though. :wink:
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