Behind the Orange Curtain

In this week’s post I have decided to address some very technical, often confusing and even more often misunderstood concepts in digital video; color space, chroma sub-sampling and gamma.  (see I told you it would be techie)  These concepts have become more important to understand recently in light of the new “digital cinema” cameras like the RED, SI-2K and the new Varicam that have brought “film-like” workflows into the television world.  The fact is that these cameras can capture much more than our current HDTV systems can display.  The challenge then for those doing high-end production work is how to retain as much data as possible through the post-production process so that we can maximize the look of the final product.

Color space refers to how color values are represented.  In the television world (which is the only one that I will address here), there are two options, RGB or YUV.  RGB is found in high-end formats like HDCAMSR and YUV is found in most others.  RGB is the purest form of representation but requires the most data to store.  YUV allows for greater compression, which is why it tends to be so popular in the digital video world.

Chroma sub-sampling has to do with how much chroma information is lost relative to the luminance information when recording in compressed formats.  In 4:4:4, everything is given equal weight, whether in YUV or RGB.  In 4:2:2, 4:2:0 or 4:1:1 the amount of chroma information sampled is less.  Here is a diagram that may help you understand what I am saying.

HDCAMSR is one of the few formats that will allow recording in RGB color space with 4:4:4 chroma sampling.  If your budget allows, this is the best quality path to go down.  A competent post house that is up to speed with RED and SI-2K workflows can convert these cameras files to HDCAMSR in 4:4:4 for high quality mastering.

Lastly, is gamma.  Gamma curves are applied to video signals to allow the captured content to be properly displayed on various monitors.  The problem with this in recording formats is that applying a gamma curve to the image before recording does not always preserve the maximum amount of information throughout the post-production process.  These newest cameras can all acquire in either a RAW or logarithmic format (like Panasonic’s Film Rec gamma), which will look very odd on a monitor, but allows the maximum amount of dynamic range in the recording.  Use of one of these types of gamma requires that a look up table (LUT) be applied to the output when doing final color correction.  This is a normal part of the workflow if you are using products like Autodesk’s Smoke and Fire or Apple’s Color.  It is often difficult for many to understand why the image looks “bad and washed out” through the offline process, but the end results are worth it.

This is only a very cursory look at these concepts.  If you would like more information or have additional questions, feel free to contact me through Post Factory.