Sorry I really need to understand this 0-255 vs 16-235

I know I’ve posted about this recently but I am certain a quick answer will get it through my skull properly… Apologies if this is unnecessarily using up forum/dev space and time…

I need confirmation this is doing what I think it’s doing. That’s all.

I have a Sony Camera which can aquire in both 0-255 as well as 16-235 using the different Picture Profiles. I’ve done lots of tests and as far as I can see it does record in 16-235 and 0-255. Please see an example of the 0-255 (Even though I’ve chopped of the top of the screenshot the Luma does in fact show 0-255 in the example):

However, the file has limited next to the range in the properties. Please see below:


And the mediainfo file shows that the actual range is being recorded in a limited range as well:

This is where I’m confused. And part of it stems from my research where Dan mentions that people who are often having problems with their files not being signalled properly. This seems the case here. The MP4 file is shown both in the mediainfo file and and in the Colour Range as being Limited, that is 16-235.

The most reasonable conclusion I’ve come to understand, is this:

  • 1: The files are not being signalled correctly. My camera shoots in either 16-235 or 0-255 depending on the Picture Profile chosen. However, the files are just rendered illegally for the 16-235 and record luma in the range of 0-255 regardless.

  • 2: Shotcut doesn’t actually do anything to the files it treats all files as 0-255 and lets the dice fall where they may. That is, a 16-235 luma file is placed in the correct range by default. Hence my illegally signalled files work because shotcut just leaves the illegal data in the files and doesn’t strip them.

  • 3: I can’t see how my files can show 0-255 range if there isn’t 0-255 luma in there?

Is this correct? Thanks very much in advance for any replies.

File C0060.MP4 is definitely full range as seen in the scopes.

Correct, or at least not in a standard way.

It will look wrong in the preview: subtle to some but not to others. It also affects export if you do not explicitly set the mlt_image_format and pix_fmt for full range.

If you apply any filter that operates in sRGB, which is most, then information (below 16 and above 235 for luma) will be lost. Track blending also occurs in sRGB.

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I’m partially coloured blind (which is what you might be hinting at?) and rely on the scopes and knowledge of lighting to guide me. Which means I’m running blind as it were.

That’s part of my worry as I’ve seen inconsistant behaviour with different filters and have seen that with my own eyes (I think the one I noticed happening on is Levels). If I change the range to full (jpeg) it just squashes the range which seems counterproductive.

I’ve been experimenting with using ffmpeg to correctly signal the files by force rewrapping them to being properly labelled. Not sure this is a good path to go down.

I don’t think it is.

On the luma scope graticule I see “100”. 100 what?

My theory is that on that scope 100 represents 100 IRE (or 100% as we now refer to it). If it does, then 100 = digital 235 per BT.709 and you’re good, as that’s where the video peaks.

If you want, I can PM you my email address, you send me the file and I’ll look at it on my custom scope and tell you what it is.

Here is the BT.709 spec. It’s pretty technical.!!PDF-E.pdf

One thing you should know is I can see clear as day on the different Picture Profiles that the one that is supposed to be 0-255, is (albeit rarely) on the scope, and the one that is 16-235 stays in the constrained range.

The tooltip says “IRE”

I see it going over 100 in the waveform, and the histogram reports “Min:0 Max: 255” clearly full range

The tooltip I’m seeing in his post says “8bitshisto.png”.

If it’s 100 IRE then that lends weight to my theory: it’s digital 235.

I don’t.

Waiting for the O.P. to send me his video file.

I mean the tooltip in the app UI.

Only when the clip is limited range. It is 255 if the clip is signaled (or changed) as full range.


So 100 IRE is 255 when full range and 235 when limited range?

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