CANON C300: Trimming White Balance, Plus a Look at Daylight vs. Tungsten Color

Cameras used to be SOOOO boring. Now every new camera is a mystery to be unfolded: What does it do well? What tweaks can make it better? Here is my first C300 article that addresses these questions...
Art Adams
By Art Adams 03.30.12

I've shot a lot of web and broadcast spots on the Canon 5D and while it makes pretty pictures the controls are very limited. It's also not a camera that can be used quickly. At the moment the Canon C300 is a bit of a mystery to me: before my recent tests I didn't know whether it's a 5D with more controls and a cinematographer-friendly form factor or if it's something more. My initial conclusion: it's more. A lot more. In my next few articles I'm going to take a peek inside the machinery and see what I can find. With the help of charts from DSC Labs I hope to shed some light on the inner workings of the C300 and try to figure out what its niche is.

Thanks to my friends at Chater Camera I had two days of hands-on testing with the C300. Some of that time was completely wasted as the first thing I do when I try out a new camera is work out what it does that other cameras don't do. Once I know what the new features are I can try to figure out how they work. Most of my time was spent with the camera aimed at a DSC Labs 20-stop Xyla dynamic range chart and a Chroma Du Monde as I sought to learn what all the different gamma and color matrix settings did. On my way out the door I had a chat with another DP who has shot several projects with the camera (I have not--yet) and he said something very interesting:

"I like the color in daylight much more than I do in tungsten light."

I can't walk away from a comment like that. While most cameras don't show different color responses between daylight and tungsten light, some--like the RED ONE--most definitely do.

This was a fairly easy test to pull together. First I set the camera to Cinema1 color matrix and Cinema1 gamma, as I think those will be my go-to settings for this camera and I didn't have time to test all of the possible combinations. I aimed the camera at a Chroma Du Monde chart, lit the chart evenly with tungsten light, and white balanced. I rolled some footage, put an 80A tungsten-to-daylight filter in front of the lens, white balanced and rolled again.

I don't know if this camera is representative of the entire line of C300's so what I found may not be true for every single camera. In this case both white balances were tinged green:

Tungsten white balance. Chart is lit with two Arri 650w fresnels. Camera white balance said 3200K.

Daylight white balance using the same setup but with an 80A tungsten-to-daylight filter in front of the lens. Camera white balance said 7700K.

This isn't unusual at all. A lot of cameras do this. Even the Arri Alexa white balances cyan, which is why I use it primarly on preset--and even then I have to pull some green out of the image to suit my taste. (For daylight I use 5600K CC-3 preset, and under tungsten light I use 3200K CC-2.) The Sony F3 is notorious for white balancing with a cold green cast, and I regularly warm it up by white balancing through 1/4 CTB and 1/8 plus green gel. The Sony EX1 and EX3 are similar, although not quite as bad.

Fortunately the Canon C300 falls more into the Alexa camp than the F3 camp in this regard: the Alexa offers not only control on the blue/orange color axis (color temperature) but green/magenta (CC) as well. The Sony F3 does not, and I find that endlessly frustrating. I'd rather set my own warm/cool and green/magenta offsets and use preset all the time rather than have to white balance through gels for nearly every new lighting setup. I could use a paintbox with the F3 but that requires having a waveform/vectorscope and a really good engineering monitor, and as the F3 is the low budget alternative it's unlikely that production will spend money on those kinds of things on F3 shoots. (I have not shot S-Log on the F3 for the same reason: if production can afford color correction then we're usually shooting with a RED ONE or an Alexa. I understand that S-Log footage from the F3 looks exceptional.)

[NOTE: A reader informs me that Sony has added a green/magenta offset control in a recent software release for the F3. Yay!]

Fortunately, under the Custom Picture menu, I found an option to adjust white balance by raising or lowering the red, green and blue gains. This is exactly what I wish the F3 had. While watching a vectorscope I made some subtle adjustments and discovered that the settings

Red = 0
Green = -5
Blue = -1

corrected the green tint under tungsten light:

It also did a good job under daylight:

The daylight white balance is a little bit warmer using this tweak, but I don't think that's necessarily bad. The red channel is boosted by less than 5 units:

We're zoomed in on the white/black chips at the center of the Chroma Du Monde. The top is tungsten white balanced, the bottom is daylight. The bottom half is slightly warmer/redder. This is with my gain offset applied.

Even without trimming the white balance gains I can see a very slight shift toward red on the bottom of the image, which is balanced for daylight. The shift doesn't seem to be caused by my gain settings; it was already there.

What is more interesting is what I found when I compared the two charts:

Outer ring is tungsten, inner ring is daylight.

What to look at.

The outer chart is lit by tungsten; inner chart is lit by tungsten and filtered at the lens with an 80A tungsten-to-daylight filter. (White balance came up at 7700, which is a bit odd, but camera color temperature numbers are often skewed. Interestingly, the tungsten white balance came right up at 3200K even though most tungsten lamps emit light that's around 3000K.)

These color differences, which are generally hidden better by other cameras, are easy to understand:

Tungsten light has a lot of red in it, so it makes sense that the tungsten-lit chart would have a rich red chip. It also has very little blue in it, which explains why the blue chip is a bit dull.

Daylight is exactly the opposite. It has a lot of blue but not a lot of red, so the situation is exactly reversed: the blue chip should be more saturated and the red chip is less saturated. This is exactly what we see here.

What's odd is that green is less saturated under tungsten light and more saturated under daylight. Green is the "standard" color in light: the Rec 709 broadcast standard derives most of its luminance information from the green channel because that's what our eyes do. White balancing a camera adjusts the red and blue color channels so that their gains match the green channel, as there's a healthy amount of green in both daylight and tungsten light. Why green should be a little undersaturated is a bit of a mystery because it should be the one consistent color between both tungsten and daylight.

I took the white balanced clips into Apple Color so I could zoom in on individual Chroma Du Monde color patches to see what's going on. Turn the page to see what I found...

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