Blackmagic Forum

Hi,

for the preparation of a project my cameraman provided me with some test sequences shot on a Sony FS 7 in 4K, S-Gamut 3 cine and Slog 3. We want to determine how to expose the footage, as I have heard that it is best to overexpose it. But the footage out of the camera is cut at a videolevel of 896. Why could that be so?
Any hint would be appreciated!
Thomas

Those Sony cameras can go into "Superwhite", which may give you about one extra stop.
Check it by pulling the highlights down with curves or gain and watch the scopes.

Is every single shot cut off at this point? Are these the source clips or has some conversion or exporting taken place?

It looks like the clip is still ungraded and in log gamma so highlights/shadows will not be close to the top or bottom of the range at the moment. Try grading the shot to see how it will look so you can determine if clipping has occurred in camera.

A good way to get s-log in a decent place is to use the Color Space Transform OFX plugin then set settings to the following:

Input Colour Space:Sony S-Gamut3.Cine
Input Gamma: Sony s-log3
Output Colour Space/Gamma: Use Timeline

Tone Mapping Method: Luminance Mapping
Gamut Mapping Method: Saturation Mapping

You'll need to add further contrast but it should give you an idea how the shot will end up.

Thanks for the hints! I will try the Color space Transform OFX.

Concerning the clipping: the clips are source clips, no conversion, no further processing. Imported in REsolve as they came out of the camera memory card. All the clips are cut off at level 896. By raising the gain i just raise the video level where the clipping occurs.

Don’t raise, lower!
896 is the broadcast limit for 10 bit, just like 235 for 8 bit.

so for 8-bit videolevels on the scope should not exceed 235? Really?

That's called broadcast range, yes: actually 16 to 235 in decimal. For 10 bit it should be 64-940, I don't know why your signal is limited a bit short. Maybe the camera does that? I've seen similar effects with log from filing photo cameras, I think it was Panasonic.
Can you try to change the Data levels under Clip Attributes to "Full " and then "Video" and check what happens?
I just tried with a Sony A7RII which I had around and it goes well beyond that value in Slog-2.

You can always change your output to full range with RGB codecs, but rather tell your clients…

In Resolve you need to grade to whole scale. During export to YUV codec it's going to be scaled, so your 0 will be 64 and 1023 will be 940. If you grade to 64-940 (16-235 for 8bit) then you will end up with no real black or white in final YUV render.

Resolve always works in full range and converts this during export (if needed, eg YUV based codec).

896 for LOG footage is rather normal. It may be clipped in camera by design (940 will be max if camera is recording to limited range). Check if you can force camera to work in full range. LOG should be by my logic rather full range as this better uses whole scale of your signal.

Andrew is correct.

Resolve scopes always display the internal 32bit float RGB using a 10 bit 0 -1023 scale. 1023 on the waveform is 100% IRE level. The previous replies could be misleading.

Thanks a lot for your helpful replies!
I changed the data level in the clip attributes from auto to full with no visible effect on the clipping.
I will check with my cameraman tomorrow if there is some in-camera clipping happening and if and how this can be changed. I will post if we find something useful.
Thomas

Yes, Andrew is correct, maybe my answer was not complete enough.

I just tried to explain possible causes for limited signals from cameras. BTW, now I remember that I've seen very limited signals in V-log from a Panasonic too. Don't remember if it was a GH4 or GH5, and they may have improved that in later firmware.

BTW, how do you record the FS7? Internally or RAW?

We record 4K internally. I am afraid that RAW may be to complex for me in Postproduction as I never have worked in RAW.

As far as I understand, SLog3 encodes more dynamic range than the FS7 can record, so it is logical the camera would clip before saturating the SLog3 space. It is like Cineon in that respect.

It be very careful then to record Slog-3 with it's massive range for any scene that doesn't demand it.
You may get banding and/or pixellation if you need to stretch contrast too much in post.

Hold on, you record in log and you clip data at 896?

Did you expose correctly?

Could you share a few seconds of unaltered out of camera footage?

As a few have surmised, it's in camera clipping. Slog3 has a fixed set of values across the Sony range, and can contain more dynamic range than the @14.5 stops FS7 can reproduce. So the sensor clips before the curve tops out.

When you test your camera you really should use a wave form, built in or monitor variety. You can see the behavior clearly. The highlights still roll nicely though. You just have to learn to allow for it.

There is a new firmware due this month which changes some exposure behavior, but I have no idea if this will be affected.