Note: Log gamma does not actually increase compression, in fact it allocates exactly the sane amount of data to every stop of exposure. However it must be remembered that for every stop you go up in exposure the brightness of the scene becomes 2 times brighter. So to record the scene accurately you should use twice as much data for every stop you add. But Log does not do this, it just adds a small amount of extra data. Thus in effect RELATIVE TO THE BRIGHTNESS RANGE OF THE SCENE the amount of data is halved for each stop you go up in exposure.
So, if you have followed this article so far you should understand that we can capture a greater dynamic range than most monitors can display, but when doing so the image looks un-interesting and flat.
So, if the images look bad, why do it? The benefits of capturing a big dynamic range are that highlights are less likely to look over exposed and your final image contrast can be adjusted in post production. These are the reasons why it is seen as desirable to shoot flat.
But there are several catches. One is that the amount of image noise that the camera produces will limit how far you can manipulate your image in post production. The codec that you use to record your pictures may also limit how much you can manipulate your image due to compression artefacts such as banding or blocking. Another is that it is quite easy to create a camera profile or setup that produces a flat looking image, for example by artificially raising the shadows, that superficially looks like a flat, high dynamic range image, but doesn’t actually provide a greater dynamic range, all that’s happened is that shadows have been made brighter but no extra dynamic range has actually been gained.
Of course there are different degrees of flat. There is super flat log style shooting as well as intermediate flat-ish cinegamma or hypergamma shooting. But it if you are going to shoot flat it is vital that the recorded image coming from the camera will stand up to the kind of post production manipulation you wish to apply to it. This is especially important when using highly compressed codecs.
When you use a high compression codec it adds noise to the image, this is in addition to any sensor noise etc. If you create a look in camera, the additional compression noise is added after the look has been created. As the look has been set, the compression noise is not really going to change as you won’t be making big changes to the image. But if you shoot flat, when you start manipulating the image the compression noise gets pushed, shoved and stretched, this can lead to degradation of the image compared to creating the look in camera. In addition you need more data to record a bigger dynamic range, so a very flat (wide dynamic range) image may be pushing the codec very hard resulting in even more compression noise and artefacts.
So if you do want to shoot flat you need a camera with very low noise. You also need a robust codec, preferably 10 bit (10 bit has more data levels than 8 bit so contains more tonal information) and you need to ensure that the camera setup or gamma is truly capturing a greater dynamic range, otherwise your really wasting your time.
Shooting flat is a great tool in the cinematographers tool box and with the right equipment can bring great benefits in post production flexibility. Most of the modern large sensor cameras with their low noise sensors and ability to record to high end 10 bit codecs either internally or externally are excellent tools for shooting flat. But small sensor cameras with their higher noise levels do not make the best candidates for shooting flat. In many cases a better result will be obtained by creating your desired look in camera. Or at least getting close to the desired look in camera and then just tweaking and fine tuning the look in post.
