Acquisition Global Viewpoint – January 2020

HDR is now recording more information than we can see with the naked eye resulting in the possibility of even more fixes being applied in post-production. We’ve all heard the phrase “we can fix it in post” and there are many occasions when processing in post is essential, such as color grading, or fixing a shot that was a once in a lifetime event, but to understand why adopting the “fixing it in post” methodology could spell danger we must go back to first principles.

Although video sensor technology has improved beyond all measure over the past fifty years or so, video signals still suffer the same limitations as they have done from the earliest days of the iconoscope. That is bandwidth limitation, distortion, and noise. All three have improved enormously with the advent of digital processing, however, the effects of noise are now more pervasive than they have ever been.

All digital video processing will introduce some noise. Sometimes it might be so small it’s difficult to measure, but on other occasions it may be immediately obvious. The key point is that noise is additive, that is subsequent processing modules in a workflow will each increase the noise floor. The signal to noise ratio only ever deteriorates through processing and it will never get better.

If we take the badly exposed scene as an example, it is clearly possible to fix the exposure levels in post. The gain can be easily adjusted giving the perception of an increase in exposure. However, in this situation we also increase the noise floor of the image and the video noise may or may not be visible. To some extent, it’s better if it is.

All broadcast video is compressed to a greater or lesser extent for transmission and noise is our mortal enemy! Compression systems do not like noise as it can be difficult to distinguish it from high-energy transitions that give detail and clarity to the image, resulting in a compromise of the creative intent. Furthermore, depending on the compression system used, a disproportionate amount of data bandwidth might be applied to the noise significantly affecting the aesthetic of the whole image.

Video processing software has improved beyond all recognition and can reliably fix an incredible number of artefacts and anomalies. However, as we have seen, even with this simple example, anybody shooting for broadcast should remember the effects of applying too much post-processing and do their absolute best to record the images correctly in the first place. We shouldn’t be relying on “fixing it in post” as a credible alternative to high-quality video shooting.