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Old September 10th, 2007, 11:26 AM   #1
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Fluorescent Lighting color shift due to high shutter speed

I have some interview footage shot under a fluorescent light. The shutter speed was to high and has a color shift or "phasing" issue. I saw the thread on why this happens (http://dvinfo.net/conf/showthread.php?t=98260). I'll add a little extra here to help with keywords for people with the same problem. It is as if the white balance were alternating from warm to cool and back again. The image is very warm (deep yellowish brown) and over the next 3 seconds it becomes cool (bluish hue). In It is a contant 6 second cycle.

Here is my question: Any ideas on how I can fix this problem in post? I am editing the footage in Premier CS3 and do not have the ability to make it black and white. I only need a usable 15 second clip to identify the speaker and can fill the rest with b-roll.

Screenshots are attached.

Thanks for any help you guys can offer!! Hopefully someone has an idea FAST!!!

Attached Thumbnails
Fluorescent Lighting color shift due to high shutter speed-cool.jpg   Fluorescent Lighting color shift due to high shutter speed-warm.jpg  

Eric Dallin is offline   Reply With Quote
Old September 16th, 2007, 09:23 PM   #2
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Maybe you could keyframe some color correction so it gradually changes from one color to another. Thats all I can think of really
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Giuseppe Palumbo is offline   Reply With Quote
Old September 16th, 2007, 09:45 PM   #3
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I have an idea. Most of the frame is static, so you can duplicate it and set its blend mode to color, then create a mask (perhaps a bezier) for the moving parts. Then you only have to do the keyframed color correction on the moving part.
Emre Safak is offline   Reply With Quote
Old September 16th, 2007, 09:56 PM   #4
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Following on Giuseppe's line, the color shifting will be periodic. Review the footage on the timeline to try to work out the period - i.e., how long it takes for the color shifting to complete one cycle. Now the somewhat tedious/tricky bit:

Apply the color correction effect at one extreme of the shift - e.g, when it is most blue. Go to the opposite extreme - e.g., when it is most brown/yellow - a place a key frame there. Go to the next extreme blue and place another key frame. At this stage, you have three key frames and the color correction effect will simply go from one extreme to the other (literally) in a linear fashion (a triangle wave). The problem is that the actual color shifting is most likely sinusoidal. See attached image of the triangular and sinusoidal shapes (strictly cosinusoidal but it doesn't matter).

So, a simple linear change in the color correction may underestimate the correction required. I would try it first. If it does, then I'd start adding extra key frames to define the sinusoidal shape more accurately.

Once you've got one cycle done to your satisfaction, you should be able to copy the correction effect to the rest of the timeline.

Good luck! I don't envy you this one. Maybe someone else will have a simpler solution.

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Fluorescent Lighting color shift due to high shutter speed-cosinetriangle.gif  
John Miller is offline   Reply With Quote
Old September 16th, 2007, 10:05 PM   #5
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Post a bit of the clip, maybe, so we could try a few things.

I have a sorta weird idea, but I think it's promising.

If there isn't too much movement, this could really help a lot.

Make two layers of the footage and make the top layer set to the blending mode of color. I haven't used Premiere for a couple years now, and not since v. 6.5. However, this blending mode is available in FCP as well as photoshop, so I have to assume it is in premiere as well.

Now, you can be creative with your color correction with just the color that is much less noticable to the human eye than luminance. I would suggest actually just using an image of the frame with lighting you like and placing that as the color layer on top. See how that works for his head (which is moving). You might be very surprised. You could also blur the color layer slightly. Don't be too scared, since it really will be a subtle change to the human eye.
As for the movement, you may need to be more creative there. Maybe mask his head and just color correct that. Less to worry about than the whole frame at least.
You could also use a solid color layer to cover that part and hope it works fairly well.

The sinusoidal problem is well noted. I'd be wary of that too.
Daniel Ross is offline   Reply

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