ProRes on BMPCC4K not recording full sensor luma

The attached screenshot from FCPX shows a deliberately overexposed image from my BMPCC4K, with accompanying luma scope. This was shooting in ProRes 422 in Video mode.

The reason I deliberately overexposed was to highlight that even saturated whites - where the sensor is saturating, as clearly evident on the luma scope - are recorded in ProRes as <100 luma level.

The same saturated whites show as white on the display, as confirmed by zebras showing when the zebra level is set to 100%, and red in the false colour mode. Therefore, they should render as 100% luma (assuming 0-255 scale), or higher with 16-235 scale, on the luma scope.

They don't at most ISO settings. Not only that, but the luma levels vary by ISO setting; less than ISO 1000 they record at 80-100% depending on the ISO, with ISO 1000 recording whites at around 99%. Over 1000 they drop again, peaking again at ISO 8000. You might expect this in BM RAW, but not in ProRes 422.

I posted about this on one of the Facebook groups and got a bunch of confidently incorrect yet patronising replies from people who didn't have a clue what my question was about. Just to clarify, it's not about dynamic range - saturated white should render as white in ProRes, regardless of the dynamic range mode (and in point of fact the same thing occurs in Film mode too). It's also not about getting the exposure right. It's about the way the camera records the luma range in ProRes, and that this is different than the luma range as interpreted on the display, with the relationship depending on the ISO setting.

I'm aware of the chart showing the dynamic range response for different sensitivities for these cameras, but again, this shouldn't affect the whites as they are recorded, assuming the exposure is adjusted to correct for the change in sensitivity.

So, what gives? Is there any other camera manufacturer which records saturated whites as light greys in some ISO settings?

Screenshot 2022-05-13 at 16.24.09.jpg (654.4 KiB) Viewed 1757 times

ISO 100 on the BMPCC 4K, shooting log, maps clipped highlights to about 80%. Here's guessing that's a function of negative gain.

As you increase ISO, and the gain increases, so will the nominal value at which clipping is mapped. If you keep the camera at the "native" ISO of 400, the clipping should reach 100%.

I didn't experiment with video mode; it's likely the results would be somewhat different.

The question is, have you really recorded the ProRes file in video mode or just used the video LUT and recorded in film log? And is your camera on color science gen 4 or gen 5?

It's been like this since the beginning.

https://robsonimaging.tumblr.com/post/6 ... ith-charts

Is there any other camera manufacturer which records saturated whites as light greys in some ISO settings?

Sony S-Log, Panasonic V-log, maybe Log-C as well.

Good Luck

The question is, have you really recorded the ProRes file in video mode or just used the video LUT and recorded in film log? And is your camera on color science gen 4 or gen 5?

Definitely recording in Video. Didn't know I could change the colour science - but the firmware is up to date. Is it selectable?

It's been like this since the beginning.

Sony S-Log, Panasonic V-log, maybe Log-C as well.

Fair enough, but you expect this in log recording. With linear response modes from any other camera I've ever used, you expect to be able to use correctly-exposed footage straight off the camera without grading.

I'm just completely puzzled as to why they've done this. It's of no earthly benefit that I can see; and compressing a linear response curve into less luma range just means less flexibility in grading before you get posterisation. Plus every clip recorded in the "wrong" iso needs colour correcting. Just, why? It seems like a bug to me, but I can't believe after several years they've not tweaked a few lines of code to fix it.

The question is, have you really recorded the ProRes file in video mode or just used the video LUT and recorded in film log? And is your camera on color science gen 4 or gen 5?

Definitely recording in Video. Didn't know I could change the colour science - but the firmware is up to date. Is it selectable?

No, unfortunately not in camera. If you are on 7.3 then you have gen 5.
With BRAW you can go down to gen 4 in Resolve in the RAW tab.

I've done now a ProRes over exposed ISO test series in film/video/video extended range with my second PCC4k being on gen 5.
Download the files here:
https://laufbildkommission.filemail.com ... iiwfcmexph

I've done now a ProRes over exposed ISO test series in film/video/video extended range with my second PCC4k being on gen 5.
Download the files here:
https://laufbildkommission.filemail.com ... iiwfcmexph

So that's way more thorough than my testing but you're finding exactly what I was finding.

Looking specifically at the Video profile files, the saturated sensor is outputting below luma 100, and as low as 87. Like me, you're finding it gets closer to 100 as you reach ISO1000, and again at around ISO8000. (Neither of which are native ISOs for this sensor.)

Does this not bother anybody else who is using a BMPCC? It strikes me as a major bug feature of the encoding which affects usability and should be fixed.

Looking specifically at the Video profile files, the saturated sensor is outputting below luma 100, and as low as 87. Like me, you're finding it gets closer to 100 as you reach ISO1000, and again at around ISO8000. (Neither of which are native ISOs for this sensor.)

The camera has two physical analog gain stages, but if you change the ISO it will only change the applied gamma curve. Hence you start off with a lower luma saturation and end with the pushed luma. If then the viewing LUT is applied it would need an adapted LUT for every ISO stage. But this way it is only one. That might be the reason for this behavior.

Does this not bother anybody else who is using a BMPCC? It strikes me as a major bug feature of the encoding which affects usability and should be fixed.

I for example shoot either film mode or BRAW.

What you could try is to use the film range mode and burn in a modified LUT.

I for example shoot either film mode or BRAW.

If FCPX supported BRAW then fantastic, but I don't want to convert my whole workflow to Resolve

Out of interest, does Resolve render ProRes footage from the BMPCC in the same way as FCPX is for me, or does Resolve use the metadata to correct this issue automatically? I don't have Resolve to hand to find out.

I for example shoot either film mode or BRAW.

If FCPX supported BRAW then fantastic, but I don't want to convert my whole workflow to Resolve

That's quite understandable. BMD has reached out a few times to Apple to write a BRAW plugin for FCPX but has not got a go yet (I am paraphrasing what Cpt Hook from BMD wrote somewhere here in the forum).

Out of interest, does Resolve render ProRes footage from the BMPCC in the same way as FCPX is for me, or does Resolve use the metadata to correct this issue automatically? I don't have Resolve to hand to find out.

I believe if you just slap in the footage, apply the normalizing LUT, and export it, it could be the same like from the camera. Never tested this because my workflow is different. I color grade and then export the files for editing, obviously this workflow will provide me with final full range luma.

BMD has reached out a few times to Apple to write a BRAW plugin for FCPX but has not got a go yet (I am paraphrasing what Cpt Hook from BMD wrote somewhere here in the forum).

Isn't it annoying when vendors don't play nicely with each others' standards? DJI have dropped ProRes RAW support from the Ronin 4D because they can't license in-camera RAW from RED. If it was a box on the other end of a cable from the camera, no problem.

I know Apple want to push ProRes RAW, and BMD want to push BM RAW, but from a user's point of view they just need to get their act together and support each other's stuff. It doesn't help anybody when they won't. Shame on Apple if it's them holding it up.

Thanks for your comprehensive help Robert.

Yeah, it's very annoying.

If I find the time I'll do some tests in Resolve to see if there is an easy way around your problem.
I think you could shoot BRAW, import the footage into Resolve, apply a quick power grade (maybe better start with Gen 4 color science + a nice LUT) and then export the individual clips as ProRes. This could be done very fast, once setup to taste.

Open resolve
Shift 9 open project settings
Color management resolve color managed yrgb
Setup hdr to rec 709
Import clips
Select all
Right click create timeline from selection
Go to delivery
Custom export prores
Flag render original resolution
Flag Multiple files export
Setup pat of export
Render

And voila a correct color managed rec709 clips
If you need you can save like project preset and reuse for every project


Inviato dal mio iPad utilizzando Tapatalk