Using Channels to separate an object from its background

[Gandwarf]

Man, you are all masters of Photoshop

I am still struggling with The Gimp... and seeing the stuff you guys are using makes me jealous
Cutting out cliffs like that in 2 minutes and brilliantly at that... ack!

[RobA]

Man, you are all masters of Photoshop

I am still struggling with The Gimp... and seeing the stuff you guys are using makes me jealous
Cutting out cliffs like that in 2 minutes and brilliantly at that... ack!

Using channel separations to set up masks works almost exactly the same way in Gimp.

Speaking of which, I found a handy script Lasm's Channel Extract that will extract any/all of the channels (RGBA, HSV, CYMK, LAB) into separate B&W layers. I find it handy to quickly eyeball the best channel for separation. Here is a mosaic of the channels:


-Rob A>

[Redrobes]

Yup, I use channel separation all the time to generate alpha masks and I was going to point out CMYK too as alternatives to get the best contrast so kudos again to Rob for pointing out a nifty way to see them all at once. After a while you just instinctively know whats going to be the best based on the colors in an image tho.

Another tip I could just shove in at the last minute which you might have mentioned cos I didn't read it all that thoroughly.... When you have your greyscale image from the separation, I used to use brightness and contrast to do the black and white range expansion but I find now that I get a dropper out and check the brightness just at the point where I want to separate it and then use a color curve and draw a box filter right at that point. Save faffing about trying to get the value right.

I'll dish some rep in a mo...