XDCAM-EX Gamma Settings

I worried about and noticed in practice an effect where if I was using CINE gammas on the XDCAM-EX and exposed for faces at 70% (by zebras) then the gamma rolloff would result in “pasty-face” appearance.  It does …and did…  The solution for good looking faces is one of the following:

  • Under-expose in shoot, raise in post.
  • proper-expose in shoot, use standard gamma (not cine gamma), be careful not to let the face hit the knee (?) e.g. set knee to 90% or 95%.
  •  take a given gamma curve (or even a flat standard one) and tweak it using gamma level & black-stretch adjustments etc. until it fits the scene.

Googling on [xdcam-ex gamma ire faces] yielding all the following.

  •  http://provideocoalition.com/index.php/awilt/story/ex1_gammas/
    • “… the cine gamma round-off and the associated smooth desaturation set in at a comparatively low level, say, around 80%. But you’ll often have skintones at or above that level; skintone highlights will often reach up into the mid-90s.”
    • “With a normal knee, the entire skintone range (short of specular highlights and glare) is usually within the linear part of the tonal scale, so faces retain a warm, saturated, natural look. Overexposed highlights intruding into the knee area will show strong tonal compression, but if your knee point is set up in the high 90s or so, the affected area will be fairly small. Also, most knees don’t do much with saturation; what typically happens is that overexposed areas start clipping in one or more colors, so skin typically goes a bit yellow just before blowing out completely.”
    • “If you use Sony’s cine gammas on those same faces, and keep the same levels, more bright areas of the face (or other skin areas) will show some tonal compression and some desaturation. As the compression sets in a bit earlier, more of the face will be flattened and desaturated: by comparison to the “standard” look, skintone highlights aren’t as vibrant and contrasty and colorful. Faces can look a bit wan and washed out, without that ruddy, saturated,“glow of good health” “
    • “…most of the Cine gammas depress midtones without changing exposure, so that skin tones will often be low enough to avoid the compressed region. But for video use, you’ll either need to pull those midtones up in post or increase the exposure to put the skintones back where we’re accustomed to seeing them. The former can’t be counted on unless you are the editor, and the latter just brings the faces up into the compression zone again.)”
    • “… the cine gamma look is a bit more “true to life”; it handles overexposure more gracefully, and … looks a little bit more like the way film handles highlights. But when compared to the standard gamma … faces don’t look as good, at least as long as you avoid overexposure.”
    • “If you’re shooting people and pretty much putting their skin tones throughout the upper half of the tonal scale, you may very well prefer using the linear standard gammas with a sharp knee affecting only the very brightest bits of the picture.”
      • Consistent with what Alistair Chapman uses for “everyday shooting”.
    • “…you might use cine gammas to keep a naturalistic sky when shooting establishing shots outdoors with uncontrolled, contrasty light, but switch to a standard gamma just for the close-ups, where the attention is focused on the face.”
  • http://www.dvinfo.net/forum/sony-xdcam-ex-cinealta/129622-skin-tones-clip-early-ex1.html
    • “The default value of 70 for zebra1 on skin tones will give them a washed out look with no detail.. almost like fake or plastic skin. I keep mine at 60 to 65 percent and I tend to use Cinegamma 4 a lot. It behaves more like a standard gamma except it rolls the highlights a bit more than standard gamma. … I see the same problem shooting in DVCAM mode with the same gamma curve.”

Here’s an alternative approach: take a given gamma curve and tweak it using gamma Levels etc. until it fits:

  • http://marvelsfilm.wordpress.com/2010/05/14/how-to-perform-on-set-in-camera-hyper-gamma-adjustment-with-hd-cameras/
    • (use) a gamma curve that – initially – gives you the flattest look; e.g. the Cine Gammas. Choose a gamma that offers you the maximum latitude possible for your specific camera. Since you have full control over the behavior of the gamma curve with the controls mentioned above, there is usually no need to choose a different gamma curve; unless extreme conditions require so.
    • For Sony EX1 & EX3 cameras, use Std gamma 3 0r 4, switch off auto-knee, set knee to 88, slope to +15.
    • Set gamma level – middle part of the curve:
      • Some cameras offer a course and detailed control over the gamma curve. The Sony EX-1 for instance has a “Level” adjustment on the same menu-page as where you define the gamma type. Use this gamma level for this step.
      • Since human flesh tones generally fall in the middle section of picture signal and gamma curve, we can use a human face or a dedicated grey card to adjust the 50-70% range. Use either a waveform monitor, zebras or histogram to monitor what you’re doing. Adjust the gamma level so that the skin exposure or test card falls in the middle range between 50 and 70%. Highlights on skin can easily go up to 70% but leave it at that max for this specific procedure. Bringing the gamma level up will increase the brightness of the middle range and lowering the gamma level will bring it down.
    • Set black-gammal-level – lower part of the curve
      • Instead of crushing blacks and doing other terrible things to the signal, we now continue to adjust the lower part of the curve – the shadows – using the Black Gamma setting.  With this we control how the lower part of the curve behaves
        • Dialling it down makes shadows darker and reduces detail in these areas.
          • (e.g.) to obscure noise and other unwanted information from the darker areas of the picture.
        • Dialling it up makes shadows more grey and will show more information.
          • e.g. during night shots, extra information can be extracted by raising the black gamma level.
    • Use your eyes!
    • This is a really good site by the way, with links e.g. to its own articles on matrix settings for Tiffen T1 (green tint) compensation in-camera.

The nature and recommended usages of XDCAM-EX Gamma-Curves:

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