Adjust alpha

[wizofaus]

Hi,

Is there a way of selecting an area of the image and adjusting ONLY the alpha channel to make it partially transparent?

The gradient tool can do a transparency gradient, but it seems odd that I can't just set it to all the same level of transparency.

Actually what I would really like is the ability to translate saturation into transparency levels - i.e. anything white should be fully transparent (alpha = 0), whereas as the color increases in saturation, the alpha value is increased. This is useful for taking images that are designed with a solid background color that use shadowing effects and converting them to transparent-background images.

Thanks,

Dylan

[pyrochild]

Is there a way of selecting an area of the image and adjusting ONLY the alpha channel to make it partially transparent?

There are several plugins that can adjust the transparency channel, including BoltBait's Transparency plugin, and my Curves+. Search the Plugins sub-forum for "alpha" or "transparency" for more.

Actually what I would really like is the ability to translate saturation into transparency levels - i.e. anything white should be fully transparent (alpha = 0), whereas as the color increases in saturation, the alpha value is increased.

For that, you specifically want my Curves+ plugin. Open it up, choose Advanced transfer mode, choose Saturation as the input and Alpha as the output, and adjust the curve appropriately.

[pyrochild]

Alternately, you can download the attached ZIP file from this post, extract the XML file from it, and load that into Curves+.