Black turned into brown?

YesMaestro wrote on 12/5/2008, 12:56 PM
I just finished shooting a subject on green screen with an EX1and everything looked fine on the LCD screen. My trusty JVC monitor is currently being serviced so I couldn't use it. When I brought it into Vegas, the subject's black pants look brown. The pants weren't the exact same shade of black as the jacket but not this far off. Any suggestions as to how to fix this and why this occurred?

Paul

http://www.themediazoo.com/Green2.jpg

Comments

musicvid10 wrote on 12/5/2008, 1:10 PM
Just a crazy guess here -- synthetic dyes can reflect UV, so under bright lights the colors may be strange. If that is the problem, it might be solved by placing a standard clear UV filter over your lens.

As far as correcting your shot, I'll leave that to the masking experts amongst us.
farss wrote on 12/5/2008, 1:23 PM
Were you using tungsten lights by any chance?

The EX1/3 suffers from a problem with infared contamination. Different materials reflect IR differently causing a magenta shift.
An IR cut filter is kind of mandatory on these cameras, I use the B&W 486 slim filter under the lens hood. I never take it off the camera.

Also worth a mention that using tungsten lights for lighting a key is not optimal.

Fixing the problem in post is very difficult, You do need to mask out the offending item(s). Good luck.

Bob.
musicvid10 wrote on 12/5/2008, 2:02 PM
Ahh, so it's IR rather than UV in this case. Thanks Bob.

One quick and dirty approach might be to use the Color Corrector in Vegas to cool down the darks only. It's worth a try.

Edit: Try Low settings of 302.5 Angle, .250 Magnitude, as a starting point. Not perfect, but less objectionable.
Xander wrote on 12/5/2008, 2:09 PM
Looking closely at the picture, the trousers are definitely a different color to the jacket - that is a manufacturing defect. Look at the border between the two and the color follows the item. The above reasons exasperate the issue. Personally, I would use AE for the color correction of that.
farss wrote on 12/5/2008, 2:18 PM
"One quick and dirty approach might be to use the Color Corrector in Vegas to cool down the darks only. It's worth a try. "

Been there, tried that
Trying to correct only part of the lowlights is the problem. There's some classic posts about this on DVInfo. Take a black object made of natural fibre with synthetic trappings. One shifts, the other doesn't. Good luck trying to use any CC tool to pick one and not the other. General consensus from those even with the skills and the high end CC tools is to either live with it or shoot it again.

Bob.
musicvid10 wrote on 12/5/2008, 2:28 PM
Oh, I never thought I could correct one color without shifting the other; I said "quick and dirty" because I was talking about moving the low balance toward the cool side to make the difference between the two less apparent visually. If you have a minute, try the numbers I posted above. "Not perfect, but less objectionable."

Building a mask is the real, but labor-intensive, solution.
YesMaestro wrote on 12/5/2008, 2:36 PM
Yes I was using tungsten light Bob. Unfortunately, that's the only light setup I have. I've been thinking of getting a new lighting kit. I guess this is a good reason as any to get one. I'll order the IR filter as soon as B&H opens Saturday evening.

I'm not looking forward to try and mask it out and color correct it because she initially walked on from camera right. Ugh!

Paul
kairosmatt wrote on 12/5/2008, 2:39 PM
How does tungsten lighting affect keying?
Yoyodyne wrote on 12/5/2008, 2:59 PM
Hey what about this:

http://www99.pair.com/yoyodyne/vegas/

Just a VERY quick pass in Vegas (chroma key and Secondary cc)

The key is meh but fixing the pants...

Instead of masking the pants and following her around with mask keyframes try splitting her in half with a mask. the top mask is her from the suit bottom up and the second video track is her from the pants down. If you get lucky with the hands maybe you can just take all/a bunch of the saturation out of her "lower half" to create the black.

Just a quick 02 - good luck
farss wrote on 12/5/2008, 4:38 PM
"How does tungsten lighting affect keying?"

The key uses a primary color, green or blue.
Tungsten light shifts the key color towards skin tone making it harder for the keyer.
Also worth a mention that every imager used for video that I know of is less senstive to shorter wavelengths. To WB under tungsten light the camera has to increase the gain in the blue channel and that means more noise. That too doesn't help a key.

On top of that daylight light sources are more efficient that tungsten. Less heat = cooler talent and crew. Tungsten lamps need to time to cool before you move them, that can slow you down.

Bob.
Serena wrote on 12/5/2008, 7:58 PM
Why not tungsten? This is the article of which farss is thinking.
http://www.bluesky-web.com/greenscreen-6.htmWalter Graff: green screen & skin tone[/link]
farss wrote on 12/5/2008, 8:22 PM
Thank you,
I should bookmark all the treasure trove of articles I can recall but never explain as well as the original author.

Bob.
Serena wrote on 12/5/2008, 9:01 PM
That's one of my resolutions also, but I can never find where I've saved the stuff. My ideas of organisation seem somewhat too flexible.
GlennChan wrote on 12/5/2008, 11:36 PM
You should be able to use the secondary CC to target the pant color, and use a very quick and dirty mask to mask off the effect if needed. Wouldn't take that long.... no rotoscoping needed, unless the talent makes some wild movements.

2- The saturation adjust filter might also work... just de-saturate low saturation colors.
farss wrote on 12/6/2008, 4:16 AM
How is any correction tool going to target the pant color, the parts that are lit by the IR are magenta, the parts that aren't are black. Luma values have a pretty wide range as well that overlap areas that you don't want shifted. Also as various light sources mix at the edges of the folds the amount of correction needed changes as well.

Even rotoscoping the mask doesn't work that well. Each edge can need different amounts of feathering depending on the angle of the fold. This is HD, not fuzzy SD NTSC, every pixel is visible.

The saturation adjust doesn't work either, you end up desaturating all the lowlights, yuck. Even within the fabic there's a shift accross the thread of the fabric. Drop the gross saturation of the fabric and it looks wrong, the texture changes,

The talent doesn't need to make any wild movements, black clothing has folds and creases. They move a LOT and aren't the best things for trackers to lock onto even if you've got them, even if they could they're still not going to help much.

I've spent a few hours trying to correct this problem. Others with more experience and better tools than I've mastered have also declared it a nightmare to fix. There's plenty of samples posted over on DVInfo although they're just frame grabs I'm certain someone will oblige you with some footage to have a go at, if not I can shoot some for you.

On the other hand the IR cut filters can introduce a green vignette offset at the wide end of the lens. That is a piece of cake to correct compared to the problems IR contamination creates.

Bob.
GlennChan wrote on 12/6/2008, 12:46 PM
Here's what's possible in Vegas:
http://www.glennchan.info/Proofs/forums/sony/Green2-fix.jpg

veg:
http://www.glennchan.info/Proofs/forums/sony/green2-fix.veg

We can cheat and it should probably work. I dont have the original footage so I don't know if noise is a problem... if it is, you can try to blur/erode (or blur + color curves and other craziness in Vegas) the matte until it works.
farss wrote on 12/6/2008, 3:29 PM
I think you and me are talking about different matters.

Certainly in the very low res frame from the OP fixing that minor offset is pretty trivial. I was speaking in general because I'd hate any EX owner to think they mightn't get themselves into serious bother not using a IR cut filter and hoping to fix it in post.

I've shot a stage event before I put the filter on my EX. There's shifts in the blackout curtains, shifts in parts of the covers on the foldback monitors and varying shifts in the talents clothing. Fixing one frame of it is trying enough, 3 hours of it is beyond the pale with people dancing around. The problem was made worse by the mixture of IR rich tungsten lights and HID lights used to light the stage.

Another problem someone emailed me footage of has a tungsten light being switched on and off repeatedly. It only lights part of the talent but that's not the worst of it. As the lamp heats up the shift varies over a few frames. Again not a trivial task at all.

I'm certain that any shot that must be rescued can be however your initial post read to me like IR contamination was a trivial problem easily fixed in post. My point was that it's much better to deal with the problem at the source because it might not be easy to fix later on.

Bob.
GlennChan wrote on 12/8/2008, 12:46 AM
I think you and me are talking about different matters.
Got it. I agree that getting rid of IR in camera is definitely the way to go... and it renders in real-time and takes no effort in post. :)