A while ago (march) I posted about colorisation using painted layers and "overlay" mode in Gimp (instead of using duplicated-and-colourised layers).
http://www.rootschat.com/forum/index.php?topic=86634.msg5257755#msg5257755Following some recent wonderful colorised images:
http://boredomtherapy.com/colorized-history-photos/my interest in colorisation was renewed.
I had never fully understood overlay mode (although it seems to work beautifully), so I read the manual. It became apparent (I'm a mathematican and programmer) that overlay mode is purely mathematical. It's just a complicated formula. This led to a sort of important thought.
Given a colour image, it's easy (in virtually any package) to make a monochrome version of it.
I have written an imagemagick script that, given a colour image and mono image will
create the colorlayer that when used in overlay mode on the mono will recreate the colour image.This means that, at least for self teaching purposes, it is possible to see what a
perfect colorlayer would look like. As guidance, I think this is valuable in the extreme.
I have attached an example. To demonstrate it to yourself, go into Gimp and load the mono and the colorlayer as layers, with the colours on top. Set the color layer's mode to "overlay" and watch the magic.
BugBear