Low contrast modes are popular with DSLR cinematographers wanting to extend the dynamic range of their footage. It seems a good idea in theory - but does it really add up? Phil Rhodes investigates
Recording pictures which look, on conventional monitoring equipment, as if they're very low in contrast is a popular technique. A discussion of the origins of this approach is complicated by the fact that many early video standards used various types of contrast processing not only to improve perceived image quality in a world of analogue broadcasting but also because of intrinsic technical limitations and the sometimes-esoteric behaviour of the available equipment, and it's complicated further by the lack of standardisation and frequent use of misnomers in current practice. Few if any cameras, for instance, really produce a precisely logarithmic output, and even if they tried to, it's difficult to make comparisons against a theoretically linear image because few sensors actually give us one to begin with. Manufacturers tend to do what they think makes their equipment look best, which might be fine, but what it means is that this is not, or at least not yet, a field of absolutes.
Canon Neutral Image
Canon Standard Image
Brave attempts to implement it on DSLRs
But in the broadest possible sense, the idea of recording an image of wide dynamic range such that it can later be processed – via grading – into a viewable image of conventionally appropriate contrast is now widespread. So widespread, in fact, and so fashionable, and so identifiably a technique of the high end, that people have for a while been making brave attempts to implement it on DSLRs. Perhaps the best-known example of this is Technicolor's Cinestyle, a picture style intended for use with Canon's DSLRs. First released a few years ago, it was seized upon by the DSLR community who immediately began comparing it to the flat-looking output of high end cameras in log mode, as viewed on a conventional Rec. 709 video display. There have been many other, similar attempts to persuade cameras like the 5D marks 2 and 3 to produce low-contrast, maximally-gradeable images.
The mathematical approach taken by the best examples is to ensure that each stop of dynamic range occupies the same number of code values in the file. This is an approach we discussed here on RedShark a while ago, using the Blackmagic Cinema Camera with its factory-defined log setting, and it's very valid. Not only does it produce something that looks subjectively low in contrast, it also ensures that potentially useful image information particularly in the highlights doesn't end up being compressed into just a few code values by the aggressive contrast of Rec. 709 or any similar harsh, video-oriented configuration. These standards don't specifically destroy dynamic range, at least not in the main, but they certainly do try to reduce the brightness of the very brightest areas of the scene to a point where conventional displays will produce an image that a standard observer will consider normal. Attempts to alter this, by stretching those highlight regions back out, for example, will quickly encounter precision and noise problems as a result. Recording log, or something like it, avoids the issue of having a video-oriented encoding destroy lots of highlight precision, even if it doesn't absolutely clip information.