There are few if any decent tutorials on how to chroma key a green screen image in Photoshop. In fact, I couldn’t find a single decent one, so I created my own.
One of the problems with many 3D programs I use (specifically KeyShot and Vue), is they don’t render out a transparency channel with the alpha. So the light bulb shown below only has an alpha channel showing the silhouette of the bulb, with nothing in the interior. So, the challenge is to how to render an image which can be post processed in Photoshop so that the interior transparencies are preserved.
This tutorial does a good job of explaining how to take a green screen image with transparencies, like a glass or a light bulb, and create a really nice mask for compositing over all sorts of other images. This is great for creating transparent PNG files which you can use in presentations, or on websites, or in advertising. Hope you enjoy the tute..
Creating a Transparent Green Screen Effect using KeyShot or Vue and Photoshop
First of all, create a glass model and set the background color to GREEN 0,255,0 RGB. This supposes you have little to no green in your original image. If you have green in your original image, then can use RED (255,0,0) or BLUE (0,0,255) for a background color. Set up your render so the final looks like this, and save as TIFF or EXR with Alpha or some other non destructive format. Do NOT use JPG!
After you have the image rendered, open it in Photoshop and double-click on the Background layer to change the name so it is editable for transparency.
Choose the Channels tab and Ctrl-click on the Alpha 1 layer to select the lightBulb. Invert the selection (Ctrl-Shift-I) under the selection menu and delete. Now you should have only the green bulb.
Change the Mode of the image from RGB Color to Lab Color (Image > Mode menu) then duplicate the a layer by drag dropping it onto the new layer icon. You should now have a new layer named “a copy."
Switch back to RGB mode (Image > Mode menu) and then ctrl-click on the ‘a copy’ channel layer to select it, and with the Green bulb showing, click the Layer Mask icon to add a layer mask. Your layer should now show a gray mask.
Add a background layer. It can be a photo or a solid color, but something which you can use to view the transparent object through.
Now for the magic. First, let’s get rid of the green hue. Click on the RGB channel (the green light bulb on the left) of Layer 0, and then open the Hue/Saturation dialog (Ctrl-U or Image>Adjustments>Hue/Saturation menu). Select ‘Greens’ and then slide the Saturation slider all the way to -100 and press OK. All the green is now removed from the light bulb.
Now, the problem is the object is transparent throughout. To fix this, click on the Layer Mask for Layer 0 and open the Levels dialog box (Ctrl-L or Image>Adjustments>Levels menu). Check to make sure the Channel is named Layer 0 Mask then click the Auto button to auto set the histogram sliders. Then select the right most slider and drag it to the left, all the while watching your image to find the correct point which looks natural. Press OK and now you should see your light bulb at full opacity at the base, but clear in the transparent areas.
Lastly, I’ve created a new layer (Layer 4), and with the brush settings shown clicked a couple times in Layer 4 to create a nice bulb glow. If I want, I can hide Layer 3 and export this bulb as a tranparent PNG which will composite nicely with just about any presentation or background image.