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Digital Cinematography Light Illusion Forums / Digital Cinematography /

wider gamuts and finishing in smaller gamut

Author Nepomuk
Mono
#1 | Posted: 9 Oct 2016 08:50 
Dear color scientists,

I am thinking and searching about this, but haven't found a sufficient answer. As far as I understand it, even a slightly wider gamut, like sgamut3cine should give no benefit to just shooting in 709 in the first place, since the out of gamut tones must be compressed anyway and rather effect, depending on the compression process, the tones that are already in 709, like skin tones.

If shooting in wide gamut, theoretically the colorist could work with the extra gradation in the out of gamut tones of a wider gamut, but for any given color depth, there will be less data values for the tones that are already in 709, if the distribution of values is equal.

On the other hand, if you set, a Sony camera for example, to 709 gamut, what is it doing internally? The native gamut of the sensor is much wider. Would it make any difference of doing the compression in post? I couldn't see a difference in a quick test with the c300II.

When people talk about this issue, they connect log and wide gamut in one sentence to explain larger dynamic range, like they want to hide not knowing the details. Log-recording is data value distribution to output-values of brightness levels not saturation.

Would be grateful for some clarity. I feel I am missing something.

Thanks,
Nepomuk

Author Steve
Scene
#2 | Posted: 9 Oct 2016 09:03 
Shooting with a wider colour gamut is basically the same as shooting a high dynamic range - it provides more options when grading.
As with shooting lower dynamic range, shooting a smaller colour gamut (Rec709) means colours outside Rec709 are clipped, not re-mapped.
The granularity of the image (the number of bits available for a given amount of colour) is not an issue, so long as the bit depth used is big enough, and is maintained big enough throughout the image processing.

Steve

Author Nepomuk
Mono
#3 | Posted: 9 Oct 2016 09:31 
Thanks for the quick answer.

I thought dynamic range is clearly defined term.

Not all cameras offer a 709 gamut, but if they just clip, of course that wouldn't be ideal, but still you need a scene that exceeds 709 to become an issue, right?

What about 8bit? Shooting sgamut3 instead of 709 gamut must be problematic?

Author Steve
Scene
#4 | Posted: 9 Oct 2016 10:04 
Both dynamic range and gamut are well defined terms.
High(er) dynamic range,m and wider(er) gamut are basically the same, but in different directions...
Scene image (having colours beyond Rec709 gamut) is not an issue, as if the camera can't capture all the available gamut, it will clip.
This really happens in the real world - just with colours such as neon signs, and similar.

Low bit depth can be an issue in any image format!
To use 8 bit on ANY high dynamic range, or wide gamut image, will exasperate the issue, and potentially cause banding type artefacts.

Steve

Author Nepomuk
Mono
#5 | Posted: 9 Oct 2016 10:33 
Sorry for insisting. I understand the theory. But "basically" doesn't mean equal. Why mix up terms? If you dump it down, I start to not understand.

To further insist: Wouldn't shooting 709 instead of sgamut3cine give more used data values, if the scene gamut does not exceed 709?

I am trying to understand here, if it is beneficial to choose the best gamut for a scene and recording format like choosing the right log or gamma curve
for a scene's dynamic range. Luckily not every camera offers that many options like the Sonys...

Appreciate it, Steve.

Author Steve
Scene
#6 | Posted: 9 Oct 2016 10:37 
If you are using an 8 bit camera you 'may' have issues with banding artefacts is you use a high dynamic range, and/or wide gamut.
(Both are different, but very similar in the issues you face.)

But, there is no guarantee you WILL have issues, as that will depend on the scene being captured - does it have large areas of smooth gradient for example?

With 10 bit and above, there will likely do no issues.

Steve

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