May
One of the things that most confuses audiovisual professionals in both the camera and post-production worlds is the difference between DATA RANGE and VIDEO RANGE signals (also called extended and legal or RGB and 709 or…) and super-whites and super-blacks.
Without wishing to expand too much on a subject that has already been much talked about, I would just like to focus on the importance of these “supers” and their maintenance (or not) in the post-production chain.
In a VIDEO RANGE signal (I put it in capital letters because it is in my opinion the best of the many ways to name this) the black and white points respectively in the values 235 and 16 (8 bits) or 940 and 64 (10bits). But this does not mean that there can be no camera signal above or below these values, these signals are known as super-white or super-black. The clearest example is the SMPTE bars that you have in this article, this signal is encoded in VIDEO RANGE and yet has super-blacks in the lower right (the extreme left bar of the PLUGE, marked in white).
During the post-production process it is of vital importance to preserve these “supers” if the camera has captured them up to color correction, because although they are “illegal” values (current digital television broadcasting does not support them), they are still usable information during color grading.
So, if we are working for television and these “supers” can’t be broadcast, why don’t we cut them from the beginning? It depends on the type of production we are doing. If we are doing something that we know is not going to be color corrected (no matter if it is done in a video editor or in an ad hoc program) then we will avoid these “supers” from the camera itself or cutting them later in the editing (using a “broadcast safe” filter) But if on the other hand there is going to be a color grading process then the supers will be useful in this process, what we will do is to “legalize” the signal by compressing these values instead of cutting them. The difference is perceptible to the eye, a target that has been cut off the “super whites” is metallized, while if it is compressed by hand the information is recovered and no artifacts are produced.
The other day I discovered on the website of Nick Shaw, an English postproducer, an interesting test file to follow the “super” during the postproduction process and check that they are not cut at any step.
If you open the file in quicktime player you will not see the “supers” (the player does not show them) but if you put it in a program that does read them you should see this:
With this waveform you can see the differences between legal and “super” values.
And remember that we go into all these topics in depth (and many others) in our codecs course and in a more practical way in the color correction course.
You can download the video file here: Super white black test
