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Filed under: Cameras •Editing •Post Production •

Green/Magenta?

Art Adams and I have observed here on PVC that the RED ONE seems unusually sensitive to green and magenta colors. The topic keeps coming up on the cinematographer’s mailing list, too, and on reduser.net. I decided to compare the R1 to several other cameras under a variety of lighting conditions. I got more than I bargained for.

Introduction

Both Art Adams and I have noticed that sometimes the RED ONE (R1) overemphasizes the green/magenta axis. I saw oversaturated foliage in an three-camera test earlier this year, and exaggerated green and magenta rendering during our IR filter tests. Art has noted green spikes when shooting under fluorescents, as have other R1 users.

Anecdotal evidence is fine, but proper testing is more useful. I assembled a motley collection of cameras, using both CCD and CMOS imagers, a selection of different lighting instruments, and three helpers: the patient and long-suffering Tim Blackmore, Art Adams, Simon Sommerfeld… and Barney, a toy bunny who tends to go green when Tim goes magenta.

Tim lights, Art measures the light, Simon supervises.

The Cameras

I had quite a variation in cameras, ranging from a $900 consumer one-chip to a $42,000 broadcast camera.

• Sony PMW-EX1: 1/2” 3-chip CMOS. Standard matrix, Cine Gamma 4. $6,500.
• Sony HDW-650F: 2/3” 3-chip CCD. Standard matrix, Standard Rec.709 gamma. $42,000 (plus lens).
• Canon HF11: 1/3.2” 1-chip CMOS. Standard matrix, Standard gamma. $900.
• Panasonic AG-HVX200: 1/3” 3-chip CCD. Cine-like matrix, cine-like V gamma. $5,500.
• RED ONE, firmware build 16: S35mm-sized 1-chip CMOS. Processed in REDCine using the default Rec.709 matrix and gamma. $17,500 (body only).

RED ONE, Canon HF11, Sony HDW-650F, Sony PMW-EX1, and Panasonic HVX200.

The Lighting

We collected lighting instruments you might find on a normal shoot. The idea was to get a realistically varied selection of daylight and tungsten-balanced sources, including continuous and discontinuous spectra. While you might well ask, “what about nasty office fluorescents?”, these vary in spectrum so much that it would be hard to generalize based on the results of a single test, and besides: if there is weirdness to the R1’s rendition, we should be able to bring it out in with the lights we had.

• Tungsten: a Tota-lite in a Chimera, nominally 3200K.
• 3200K fluorescent: A Kino-Flo Diva-lite with 3200K tubes.
• North light: Northerly blue-sky light coming in through a bank of windows.
• HMI: An Arri HMI in an Arri pancake diffuser, nominally 5600K.
• 5600K fluorescent: A Kino-Flo Diva-lite with 5600K tubes.
• Daylight: A mixture of direct sunlight, skylight, and reflected light from concrete paving and tan-painted wood siding.

The Test

All five cameras photographed the same scene under each of the six lighting types. The scene consisted of a ChromaDuMonde 12 chart from our friends at DSC Labs; an x-rite ColorChecker chart which appears to be the Gretag-Macbeth chart under a new name (these two charts give us “objective” references); Tim, who has shown a tendency for magenta skintones on RED; and Barney, whose fur-tones go green on RED (Tim and Barney have similar coloration to each other on most other cameras).

Tim, Barney, and test charts under scrutiny.

For good measure, Tim wore his infamous IR-radiating/reflecting shirt.

Simon Sommerfeld appears in the daylight tests; he also kindly provided the ColorChecker chart and the 8x Canon HD EC zoom used on the HDW-650F. The HDW-650F, a new HDCAM camcorder, was generously supplied by Sony’s Juan Martinez specifically for this experiment. Canon sent an HF11 along for review [both it and the 650F will be written up here on PVC soon] so I threw it in the mix, too.

Daylight tests: HF11, HVX200, EX1, 650F, and R1.

Art used his color meter to measure the actual lighting values, resulting in an actual color temperature and a green/magenta imbalance factor (essentially the vector orthogonal in color space to the warm/cool color temperature vector, measured in “correction units”: if the meter reads plus 1/8 green, you’d use a minus 1/8 green gel or a plus 1/8 magenta gel on the light to correct for it). Art’s readings were recorded and are reported below (I also read off white balance values from those cameras that reported them, and they were in general agreement with Art’s meter).

The cameras were all set to standard color matrices, with the exception of the HVX200, which was on Cine-like—I normally use Cine-like and neglected to reset it to Rec.709 colors for this test.

The card-based cameras all recorded to their solid-state cards; the 650F’s HD-SDI was fed into an AJA IO HD and captured to the internal disk of a MacBook Pro using ProRes422 HQ compression.

All clips were brought into Final Cut Pro, either in their native form or via conversion (the HF11’s AVCHD was converted to ProRes422 using FCP’s Log & Transfer; the R1’s REDCODE was output as 1080P ProRes422HQ using REDCINE with default Rec.709 matrix and gamma settings). The R1’s footage was white-balanced in REDCINE prior to export.

Once in FCP, the 3-way Color Corrector was used to tweak exposure on the DSC CDM12 to put the gray background at 50%, and set white, black, and gray balances on the CDM12’s white, black, and gray bars.

A sequence was built using a single frame of each camera’s tests under each lighting condition. That sequence was duplicated, and blown up to focus on the CDM12 chart.

The ring of colors on the CDM, displayed on a vectorscope, forms a roughly hexagonal constellation that, under ideal circumstances, traces out the same shape as the colorbar targets on the ‘scope. If chroma gain on the ‘scope is set to 1.875x, that constellation should—ideally—drop its corners exactly atop colorbar target points.

The dupe sequence’s saturation was set to 188% (while verifying on FCP’s vectorscope that doing so did not change the shape of the constellation), and screen grabs were taken of each frame’s vectorscope display.  Those grabs were imported as a frame sequence, and the original scene sequence and the vectorscope sequence were composited side-by-side.

That sequence was exported as a series of stills, and those stills are reproduced in the following pages. You can compare the pictures by eye to get a feel for overall color renditions, and look at the vectorscope plots for a more objective report on how each camera handles the colors presented to it, and how they compare to each other.

Each results page shows all the cameras under a single lighting condition. If you want to compare the same camera under different lighting conditions, you might want to load the individual pages into different browser windows or tabs, so you can click rapidly between them or position them side-by-side.

Quick jumps:

Introduction, Cameras, Lighting, Tests

Tungsten

3200K Fluorescent

North Light

HMI

5600K Fluorescent

Daylight

Observations & Conclusions

Next: Tungsten tests…

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good article!
as always…. adam is on target…

Posted by billS  on  11/23  at  04:20 AM

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Adam, I’ve been saying for many weeks now that REC709 color matrixing does not look right in any of the Red apps or quicktime translation. I exclusively use Camera RGB or Redspace. I then tweak saturation and color balance to achieve a natural looking skin tone.

Posted by .(JavaScript must be enabled to view this email address)  on  11/26  at  07:41 PM

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Very detail article. Since this was posted, what would you recommend now?

Posted by mikethebuilder1  on  07/07  at  01:22 PM

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This test was done in 2008 with build 16; it’s now 2010 and we’re up to build 30, which has radically improved the situation. The new REDcolor color space is far more accurate and naturalistic than the earlier color spaces in older firmware, and the new Mysterium-X sensor appears to use different color filtering with improved discrimination (I’m testing this right now and will be posting my findings soon), which makes things even better.

Short (and free) answer: update to build 30. Longer (and more expensive) answer: upgrade to the M-X sensor.

Posted by Adam Wilt  on  07/07  at  02:05 PM

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