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Old 10th April 2021, 17:53   #1  |  Link
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Join Date: Feb 2011
Posts: 11
colorspace - DVD with odd luma range 16 to ca. 215 - how to correct?

I'm working with a DVD which has even the brightest luma values a bit low. Bright scenes look toned down, like the material is a little underexposed. I used
to have a closer look at the numbers. And I tried to fix this issue using
Levels(0,1,235,0,255,coring = false)
because it looks to me like the the lower luma end is fine, but at the upper end someone seems to have forgotten to open up the range one time. 92% of 255 is 235, and 92% of 235 is 216,6. And it appears the upper range is about 216.

Here are some pictures of bright scenes.

Original frame 533 (this frame seems to be an exception, see my explanation below):

Corrected frame 533:

Original frame 3890:

Corrected frame 3890:

Original frame 4454:

Corrected frame 4454:

Original frame 30368:

Corrected frame 30368:

Frame 533 is a rare exception. After the correction, the upper luma value extends well beyond 235, being 252 max. and 239 loose max. However, if I understand it correctly, the luma range is just a flag and the restricted range from 16 to 235 is used so that there is some overhead. Already the lower luma end does not stop at 16 but can be found at 11, 12 14, etc.

The other bright scenes look alright with this correction, in my opinion. The maximum values are at 230, 231, 232. So still below but close to 235.

Question 1: Is this just some film material with low brightness values deliberately used or am I seeing things correctly and this is a badly mastered DVD that is worthy of correction?

Question 2: Is my way of correcting this the way to go about this or is there some better way to do it?

Quesiton 3: The graphs of the corrected frames show some gaps. Can this be done without such gaps occuring, for example by converting to 16 bit or something like this?

Question 4: Is it okay that the corrected frame 533 has a max. value way beyond 235? Will this be clipped when encoding as MPEG2 and the range set to 16 to 235?

Last edited by Lariel22; 10th April 2021 at 17:58.
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colorspace, luma

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