Re: [Gimp-developer] B&W digital, compose w/weighted color channels?
Hi, [EMAIL PROTECTED] writes: > Recently there's been a lot of excitement in the digital camera world > among former B&W film afficianodos who are simulating the use of colored > filters by manipulating color channels prior to converting a digital > image to greyscale. > > Photoshop has a feature that lets you weight color channels when > you recompose them. > > In Gimp, you can decompose color channels by: > > Image->Color->Decompose > > and then later: > > Image->Color->Compose > > I understand the function of weighting the channels is not there. > > Is there some combination of existing functions that would let > you re-compose an image as: > > 0% red, 50% green, 50% blue (i.e., a red-blocking filter) > > Is there some way to use blending of layers and opacity to do > this? Or some other tools or scripts? I'm sure there is a way but reading your mail I came up with an idea of what could be a nice feature for GIMP-1.4: What if we add an opacity slider to the channels dialog similar to the one on the layers dialog? The opacity would affect normal selection channels (where it can now be set in the dialog that pops up when you double-click the channel's name). For the red, green, blue and alpha channels it would affect the projection thus allowing for easy interactive color-correction of the whole image. Is that a good idea or not? Salut, Sven ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] B&W digital, compose w/weighted color channels?
On Monday 17 December 2001 20:47, Lourens Veen wrote: > I just realised that you could just add a layer with colour (0, 255, 255) and put it in front of your image, then set its layer mode to multiply. Much easier. Brightness might be a problem though, make sure your highest percentage is always equal to 255 (so for 25%/75% you would do 85/255) and I think it should be ok. Lourens ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] B&W digital, compose w/weighted color channels?
On Monday 17 December 2001 20:18, [EMAIL PROTECTED] wrote: > > Is there some combination of existing functions that would let > you re-compose an image as: > > 0% red, 50% green, 50% blue (i.e., a red-blocking filter) > > Is there some way to use blending of layers and opacity to do > this? Or some other tools or scripts? Maybe this is more a question for gimp-user, but since it's here...It's possible, but a bit tricky. Here's what I can come up with (using your 0:50:50 example): Decompose the image into R, G and B images. For each channel image, add a greyscale layer, black for 0% for that channel, white for 100%, or anything in between. In your example, red would get a black layer on top while red and green would get 128,128,128-coloured layers. Set the layer mode on these new layers to multiply. Flatten the R, G and B images. Create a new image the size of the others, and add three layers, a red one (255, 0, 0), a green one (0, 255, 0) and a blue one (0, 0, 255). Set the layer mode to addition for the topmost two layers. Now add layer masks to each of the layers, and paste the corresponding channel image into the layer masks. In your example, this would give you 0*R + 0.5*G + 0.5*B, which is the image you're after. The only problem I can see is that you might run into rounding errors, 8 bits isn't that much accuracy, but given the simplicity of the operation I think you should be fine. I think this would also be easy to make into a script, but I'll leave that to someone else. Lourens ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
