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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Green Screen color is below black?

J

jbeale

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I'm using the current REDCINE - [Build: Dec 10 2007] to look at the first frame of this file: A001_C001_071024_002.R3D
which you can download from ftp://redcam:red@ftp.chimney.se/RAW/green screen/A001_C001_071024_002.R3D

Notice that the unlit black sandbag has R,G,B values around 11, and yet the hot-spot on the green background has R and B values of 0 ? That may make it easier to key, but still something doesn't seem right. I did no color correction at all, default values using format Rec 709 and gamma: Rec.709
 
I have noticed that the RGB tool in the last two builds has some very strange behaviors, this is obviously one of them.
 
I should add this is not my camera, or my test, this file is from those "TheChimneypot.com" Red tests that went online a few days ago. I'm not sure when they were done, but they may have been using some older firmware- so that may be a factor.
 
Actually, its easy to tell the date by looking at the file name.

The field 071024 is in the form of YYMMDD or 2007 10 (October) 24
 
I really don't think it's the tool lieing to you. Look at each of the individual channels and you'll probably find that the channels actually are clipped.

REDCine and REDAlert both will suddenly crush the blacks in a channel if you aren't careful. Often this'll happen when tweaking the individual channel exposures.

It must have something to do with the debayer process. The only other time I've seen software react similarly is when working in lab color in photoshop. The histogram seems a lot faster in the latest build of REDCine which makes it much easier to leave it open and actually use it. If the new build is working for you I recommend pushing it off to the side to use as a guide.
 
Hey Gavin,

Are you saying that the clipped value is wrapping around and causing the RGB tool to indicate a value of 0 for one or more of the contributing channels?

Kevin
 
I know that any image capture device has some gamut of colors that it can record, and anything outside is clipped in some way. Are there settings in Redcine that would prevent the green screen in this case from dropping below normal black levels in R and B channels, or is this an "out-of-gamut" problem that no change of settings will solve? Or is this something wierd with my PC / video card (wouldn't surprise me) and the file looks ok for others? Note, I didn't actually use the RGB button within redcine, I just did a screen capture and viewed that in photoshop.

The R3D file on the FTP site I linked to is almost 100 MB so it's a bit of a download. On the other hand it's actually the second of two: the ..._001.R3D file is 2 GB, which is the largest single file I ever downloaded. Those folks have bandwidth.
 
khmuse said:
Hey Gavin,

Are you saying that the clipped value is wrapping around and causing the RGB tool to indicate a value of 0 for one or more of the contributing channels?

Kevin
Click to expand...

No I don't think it's a case of one color dragging down another. It's often very clearly limited to a single channel. If you adjust for instance the exposure of the red channel it doesn't fade out into black it'll just sort of pop out to pure black sometimes quite suddenly without affecting anything else. it's acting like it's in XYZ or Lab or something other than RGB. Like JBeale was saying: Out of Gammut is the best description of what's going on. It's like the color operations are being done in one gammut and then when converted back to RGB are a bit quirky on the low end as a result of the conversion.

I don't know the actual color science involved because RED hasn't published the design specs for how they're doing their color operations yet but that's how it looks from a user standpoint.
 
Update: in the "Format Settings" if I select "Camera RGB" instead of "Rec 709" I get much more reasonable colors on this shot. So maybe that is the proper setting for greenscreen work, I don't know. Or maybe for all work, per Rob's comment "...Camera RGB is a color space that looks nice with the camera footage." http://www.reduser.net/forum/showpost.php?p=112078&postcount=87

Also Graeme recommended Camera RGB to Macgregor, who wanted Redcine output to look like the RedAlert TIFs: http://www.reduser.net/forum/showpost.php?p=106383&postcount=4

Meanwhile I have a different problem as you can see below (ravenous pixels devour the helpless heroine), but since no one else is complaining of this, I'm sure it's just my lower-than-low-end hardware setup.
http://www.reduser.net/forum/showpost.php?p=124292&postcount=25
 
Rec. 709 might not look right depending on your monitor setup etc. Also keep in mind that redcine will load color processing settings from the camera that might influence this (white balance, gains, exposure, etc.). Make sure these are set right as well.

It might be that it just wasn't exposed properly. Can take a bit of practice to get it right with the RED ONE if you're unfamiliar with it.
 
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