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Filed under: Cameras •Editing •Post Production •

Green/Magenta?

Observations & Conclusions

• While none of the cameras tracked color perfectly and consistently in all lighting conditions, the HDW-650F came closest.
• The R1 showed the most variation in color rendition as the lights changed.
• The R1 does indeed overemphasize the green/magenta axis relative to its rendering of other colors.
• The R1 is comparatively oversaturated to begin with, which makes the green/magenta contrast even more apparent.
• The R1’s deep blues go purple as scene color temperature increases. Look at the lower right chip on the CDM, or the blues in the bottom two rows of the ColorChecker. Blue stays blue under 3200K light, but the 5600K, 7800K, and 11,000K scenes show increasing purpleness in those chips.

That last point is the real shocker. Why hadn’t I noticed that before? After all, we’ve done comparisons that clearly show this purple shift;  we’d just been blind to it.

John Beale may have part of the answer with his RGB spectrum plots. Note the R1’s strong blue filter “leakage” from 600-650 nm. When I download John’s Canon 20D spectrum and look at its channels individually in Photoshop, I see less such “leakage”; likewise with John’s other spectral tests.

There has been speculation on CML that RED is using RGB color filters in its bayer-mask CFA with wider-than desirable spectral windows—a.k.a. gradually sloping shoulders, shallow cutoff, low Q filters—thus leading to imprecision in color discrimination and difficulty in accurate hue recovery; John’s tests would seem to lend credence to this theory in a roundabout way.

RED chooses to differ, and has posted their response curves at reduser.net. If I interpret them correctly, they imply that John’s spectral decomposition should show no blue-channel leakage at all above 600 nm, so there’s something failing to compute (and I admit, after a full day of looking at this stuff, that it may simply be the overheated neurons in my poor little brain). In any case, the Mysterium continues to mystify.

Another part of the answer may be in REDCINE’s Rec.709 matrix. When I switch to the “Camera RGB” matrix instead, the color accuracy of our test clips improves drastically (I also boosted saturation, somewhat arbitrarily, to 1.7 to restore a comparable amount of vibrancy to the image, as Camera RGB is a wide-gamut matrix). The color rendition still isn’t perfect (in fact, the green/magenta axis is strongly de-emphasized), but the ColorChecker and the CDM look a lot more consistent across different lighting conditions. Skintones look a lot better, too. How about Rec.709 and Camera RGB in RED Alert?  The same shots, processed with the same parameters, seems to be a bit less saturated, but are otherwise pretty much the same:

REDCine and RED Alert renderings. Camera RGB has saturation set to 1.7 in both cases.

I’ve spent most of the afternoon snuffling around on reduser.net to see if others have run into the blue-into-purple issue (at least one fellow has, but he’s the only one I found), and to see if I can find guidance on when to use the various color-space options in REDCINE or RED Alert (answer: not really; the question is frequently asked, but rarely answered). I’m going to futz around with the existing clips, shoot some more tests, and explore a bit more in REDCINE, Apple Color, and/or Color Finesse, and then I’ll post a follow-up article with my findings.

In the meantime, if you have any useful insight, please post it it the comments section below. And if you’re shooting RED, try “souping” the “negative” with Camera RGB matrixing rather than Rec.709, lest your remake of “Blue Velvet” wind up as an homage to Deep Purple.

It doesn’t hurt to remember a trick the film guys use: before a major production, they’ll shoot color tests of the props, costumes, and makeup to be used. Film stocks and processing methods often have their own quirks, and it pays to catch unfortunate interactions between scene colors and a film’s color rendition before the production starts. Treating the RED ONE like an unknown film stock, and REDCINE, RED Alert , or native REDCODE support in your NLE or DI program of choice like the processing and printing, is a prudent thing to do.

Quick jumps:

Introduction, Cameras, Lighting, Tests

Tungsten

3200K Fluorescent

North Light

HMI

5600K Fluorescent

Daylight

Observations & Conclusions

(Page 8 of 8 pages for this article « First  <  6 7 8)

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