Modify the rgba data pixel per pixel on the pixmap (so load pixmap not image and load the image from the modified pixmap afterwards)
Ok thats the noob approach at least.
Interstingly, if you check the Pixmap Documentation you will find out that it supports more formats than just the RGBA format, especially the a8 format ...
Haven't checked that but theoretically you might be able to load the grayscale to a8 and draw it over the original to apply alpha (perhaps with alphablend, don't know if it works on pixmaps) and then grab it again.
Ok thats the noob approach at least.
Interstingly, if you check the Pixmap Documentation you will find out that it supports more formats than just the RGBA format, especially the a8 format ...
Haven't checked that but theoretically you might be able to load the grayscale to a8 and draw it over the original to apply alpha (perhaps with alphablend, don't know if it works on pixmaps) and then grab it again.