Now that I'm doing more filming with the 5D than still pictures the fragile H.264 codec has really become something I have to pay attention to. The luxury of shooting stills in RAW is something I found critical very soon after buying the 40D. The video codec on the 5D, however, is kind of like shooting in JPEG. You get what you get and there's not much leeway in changing that after the fact. During the HDI Rawworks lectures last weekend I found that the pro's using this camera made color choices in camera. Even Shane Hurlbut has commented on his blog about having to manually shift the white balance on the 7D...but more about that later in this post. A very good thing is that I work with some of the best color science professionals in the industry today. They deal with these issues day in and out.
If you work with 5D footage often enough you'll notice that it tends to over saturate the red/magenta/pink range of colors. As much as I appreciate red heads, not everyone is...as the camera tends to naturally reproduce with it's factory color profiles. One of my professional colleagues, who is also a high end Canon owner, commented that this is the aesthetic choice that Canon makes. Does it produce nice photos? Yeah sure, I guess. Is it a good start for video and color correction? - no. Over saturating any color causes color channels to clip and that's unrecoverable with the H.264 codec. What most people tend to do it set their camera to a neutral picture style with contrast and saturation set down two stops to compensate for color correction in post.
Is there a better way? Maybe. I set off to understand how to solve these problems for documentary shoots. Shane hits on it a little in his above mentioned posts. I was also inspired by Ben Cain's camera painting tutorials on his web site. I started with a simple shot of a Gretag Macbeth Color Checker chart shot in RAW as a still photo. I then imported the picture into Photoshop and blurred each of the color tiles to get the average neutral style color reproduction value. I also set the exposure so the bottom mid-gray tile was set to the theoretically correct value.
The chart comes with a little pamphlet with color names and sRGB values. sRGB primaries and gamma is equivalent to rec.709 (HD video) as far as I know. Even if it isn't, the videos I create are shown on the web so sRGB reproduction is exactly what I want.
Enter the Canon Picture Style Editor. The documentation for this tool is a bit obscure. In fact, the only tutorial I could find was on Canon's Japan web site. It lets you set the tone curve and color shift for up to 100 colors. The picture below shows the Picture Style Editor tool. The "S" curve in the Tool Palette is how you set the tone curve. The color wheel shown above demonstrates how a color is effected when you modify a color range (the "pie slice" is the effected range).
The tone curve, as I quickly found out, is pretty much camera specific and an aesthetic and technical choice of Canon. I chose to just use the default Neutral tone curve as a starting point and not modify it. Why? When I played with the tone curve to any significant degree I started to see artifacts like noise or loss of detail creep up quickly. Since the footage isn't RAW it's just another aesthetic choice and I chose not to adjust the curve. The legendary 5D "superflat" picture style uses the tone curve and contrast turned down to -4 to get it's super dynamic range, but leaves me wondering about the negative impact (dunno myself).
The Picture Style Editor lets you also edit colors in HSL (Hue, Saturation, Lightness). The Hue is the rotation about the color wheel (0-360 degrees), the saturation is the distance from the center of the circle to the outer circumference (center is fully desaturated), and lightness is the third dimension in and out of the circle representing brightness. Does any other piece of software edit in HSL? Not really, but the Picture Style Editor includes an RGB to HSL converter to make life at least sane.
At my first try I adjusted all the colors to the values shown on the little sRGB Gretag chart. This overcompensated for the non-linear tone curve. Long story short, it didn't work. Noise popped out everywhere and human skin looked scaly from thus noise. Ick. Keep in mind that I was adjusting color with contrast and saturation in the style set to zero (default) knowing that I was going to turn these down while filming (usability choice). The tone curve was throwing everything off. Why not adjust the tone curve? Well, the Gretag chart values assume a fixed constant illuminant, not the real world of shooting pictures in contrasty situations (another usability choice).
The answer finally came to me today. If I ignore the lightness and just concentrate on the hue and saturation I will at least have the correct color and saturation (remember the over saturated reds?...gone baby, gone). So I used the existing "L" values from the photo and the "H" and "S" values from the Gretag chart after converting them. Will adjusting the contrast to -2 in the camera effect the H,S values. Yes. However turning down the contrast is just a safety net to me. It's meant to be turned back up in post at my choosing (another usability choice).
Below is a before/after example of the custom picture style using the same white balance color temperature. The 'before' picture uses the standard neutral picture style from Canon. The 'after' picture uses the new custom profile adjusted from the Gretag chart. Yes, Brooke is likely a user of tanning cream but her skin doesn't look burned red in person, unlike the first photo would indicate. Hair and skin tones are much more real and natural in the second photo in my opinion. I tend to keep in mind that footage is color corrected anyway so absolute color accuracy is rarely required. I just want a better starting place.
Time to try this profile in some real world situations. I might pass is around and see if additional aesthetic choices need to be made. At least this gets closer and takes care of the saturated red issue.