- Posts: 11
- Joined: Mon Apr 05, 2021 9:48 am
- Real Name: David French
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?
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 1763 times