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keying white
Hi!
I had to shoot some footage in a photo studio, where we only had that white background they usually use for taking photographs. When I later checked the tape I realized that the “white” wasn’t the one I shot. It became a little grey or something, although the white balance seemed to be OK at the time of the shooting.
Fortunately, I only have to use small portions of the footage (max. 2-3 seconds), but keying haven’t succeeded yet. I tried the color picker, but when I adjust the slider, it “picks” pixels form the actor’s body as well (where it finds similar pixels to the one I picked).
Is there any trick, tutorial, or special “filter setup” to solve this problem?Laszlo
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Life is too short to drink poor wine. -
4 Replies
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Umm could you try a luma matte?
If the white has picked up enough light it might be an easier key. you could also try a garbage matte of the talent’s face and animate the keyframes if needed.
Hope that helps
Graham
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Yeah, you may need something on the lines of a moving matte somewhere between straight up roto and a garbage matte.
I imagine 2 mattes. One just inside the edges of the person. One just outside the edges. So that your luma key is just working on the edge area.
For future ref, if you know you have to key off of white, make the person’s keylight lower than what the BG is lit with. So that the BG is about a stop brighter than the person. That way you have a chance of keyeing as clean as a luma can w/out affecting the person. But even good lumas are never as good as a color key.
Chris Smith
https://www.sugarfilmproduction.com -
Thanks guys, I’ll give both ideas a shot!
Laszlo
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Life is too short to drink poor wine. -
If there’s a nice contrasty line between the background and the subject, I would export the 2-3 seconds (60-90 frames) as an Targa image sequence. Then, open up one of the frames in Photoshop, choose the appropriate tolerance in the magic wand tool, and click an area of the white to set that as your selection. Then go into the channels tab, create a new channel (it’s going to automatically call it “alpha 1”) and hit delete (or alt+backspace depending on what you have your foreground and background colors set to) that should make your selection area white, and leave your subject shape as black. Now deselect (Ctrl+D) and hit Ctrl+i to invert the colors. What you should now see in the alpha 1 thumbnail is all black, with your subject pure white. Now save the targa with 32-bit color depth.
Now, I’m sure you’re not looking forward to doing this for all 60-90 frames, but you can just record an action within Photoshop with the steps I’ve described, open all the images at once, then go to file -> automate -> Batch. Choose the action you created, and set the source to “opened files” (or something similar, you’ll have to forgive me, I don’t have the program in front of me). Once all the frames have alpha channels, import them as an image sequence into After Effects. Have a great night. I’m heading home from work now, I’ll check the forum tomorrow to see if this helped you.
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