For anything you want to do in Photoshop there are a dozen ways to do them. Greenscreen removal is no exception. If you're lucky enough to have a program like Mask Pro by On One, it will do the job nicely with just a few clicks. However, those programs can be expensive, and with just a few extra steps you can do the removal and clean up yourself. This is a method I picked up from a tutorial originally written by Ryker Beck on the old Rezzable website back in 2009 (thank you 1Angel for locating the source since my memory and HD wipe failed). However, this method continues to work well for me when I'm not using Mask Pro. If you have other methods you've found that work well for you please do share them in the comments area. I am by no means an expert in Photoshop. I'm self taught and am always looking for new/easier/better ways to do any given task.
"Greenscreen" is a generic term for any picture where the subject is photographed in front of a solid, bright/neon, primary color. Neon lime green tends to be the most commonly used, however a bright electric blue or hot pink (or any similar striking color) works as well. In Second Life the "Greenscreen" is created using a solid colored prim set to full bright as the background.
For this tutorial I am using an older greenscreen picture taken before my new graphics card, so many of the edges are not as clean as they would be with a higher end graphics card. However it still works for the purpose of this tutorial.
1. Start with your picture. You can see the solid green background, as well as a variety of colors and transparency levels in the image.
Duplicate the background layer. Select the top copy layer and then click on the eye on the original background layer to hide it.
2. Next from your menus at the top of your screen go to Select > Color Range > choose 'Selection'. Your cursor will turn into an eye dropper and just click anywhere on the background where the green would be. Check the Invert box, then ok. You'll notice the marching ants around your image.
3. Copy your selection using ctrl + c. Make a new layer, then paste your copied selection using ctrl + p onto the new Layer 1. At this point I also hide the background copy.
4. You'll notice on the new layer the semi-transparent areas still have green. Always start by working with the semi-transparent areas that have color, and then move to areas that are black and/or white.
5. Ctrl click on the Layer 1 thumbnail to select the entire image. You'll see the marching ants around the outline again. Create a new blank layer on top of Layer 1. Change the new layer (Layer 2) to Color. Go to your eyedropper tool and select a color from Layer 1 that is next to the green that you want to replace. In this case I have a few areas of red in the hair, tan, yellow, blue on the wings, and brown that still have a green edge to them. One by one I select each color sample from the base image, choose my paintbrush tool, a small soft brush and 100% opacity, and paint along the edge. You'll see the green gets covered up with the selected color.
6. After you've painted away the green in all the color zones (leaving only the semi-transparent areas that are either black or white) you can merge your top color layer 2 with the base layer 1. At this point you can use deselect to remove the marching ants outline.
7. Now we want to remove the green from the semi-transparent black and/or white areas. Go to Image > Adjustments > Hue/Saturation. From the drop down box select "Greens". Move your Saturation slider all the way to the left. If you are working with black, move the Lightness slider all the way to the left. If you are working with white, move the lightness slider all the way to the right. Click ok.
8. And there you have your image completely extracted from the Green Screen and ready for any other work you need to do on it in Photoshop. I always create a new layer below the final image and use the paint bucket tool to make it solid black or white to check my image and make sure all the green was removed and I didn't miss any spots.