Thanks guys.

I have to note two things:

1) there's a slight flaw in the luminance script, which actually is due to gimp's limitations on colour management and layer modes - if the layer you extract luminance from has very bright and saturated colours, for example bright yellow (ffff00) then it the resulting image after extraction will have a slightlky lighter shade of yellow. This is because the grain merge mode works as a simple addition - it basically converts the layer colour to a signed byte (-128 - 127) and adds it to the image colour. So when you have a yellow that has high luminance, but the blue channel is already 0, not enough luminance gets extracted from it, since the blue can't go any lower... and the grain merge mode will still add value to the blue channel.

I'm not yet sure how to fix this, but I have some ideas and I'll be working on it. I might even completely rewrite this script... I'm looking into manipulating layers directly by pixel regions in python-fu... so stay tuned on it. Meanwhile, this script works fine if you don't have any really bright & saturated colours in the cyan-green-yellow range.

2) Refering to O's post... when you extract the luminance and then modify the chroma layer with the h/s/l tool, you have to remove the luminance every time after adjustment from the chroma layer (with the remove-script) if you want to keep the luminance the same. The chroma layer has a constant luminance of 50% after extraction, but when you modify it with gimp's h/s/l tool, it doesn't preserve that luminance.

ps. Sorry if my explanations are rambling a bit... I'm a bit drunk atm.

I'm pretty sure that what I'm doing with your script is nothing like you had intended for it to be used.

I love being able to preserve the luminance and have the ability to change the chroma to what I want.

I got the cup here and like the option of changing the chroma layer to the color and lightness/darkness/saturation that I like.

The first one on the top left is the original coloring of the cup.

very nice "O"

Love the copper (reddish) cup.

Excellent dd!
Another fine python script.

Rod, that's gorgeous! Isn't the plug-in fun to play with?

I'm having all kinds of fun with this image. It needs to be changed from grayscale mode to rgb first.

That is very pretty O.

Thanks O.
This is one filter that i will keep secure in my box of photo enhancement tools.
Definitely a lot of fun to play with.

Borrowed your image O.