O7Q exposure problem

F

Fader8

Well-known member
Hi there,

I have just played around with some footage I shot lately and I found some problems with exposure; while the internal
footage seems to be quite well exposed, the RAW is strongly underexposed, why? Am I doing something wrong?!

Settings in Resolve: 2K Timeline, Cinema DNG, White Balance: as Shot, Color Space: BMD Film

Seems to become a noisy project :(

Cheers

FS 700 _7Q.jpgFS 700 Internal.jpg
 
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...but that makes it noisy. Why isn't the picture like I saw it on the screen?
How should i expose correctly then? Always think 3 stops over?
 
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Fader8 said:
...but that makes it noisy. Why isn't the picture like I saw it on the screen?
How should i expose correctly then? Always think 3 stops over?
Click to expand...

I guess the internal image will be noisy too if you apply your correction. Your image looks underexposed that's why you get the noise.
 
Clermond said:
I guess the internal image will be noisy too if you apply your correction. Your image looks underexposed that's why you get the noise.
Click to expand...

but the internal is not underexposed as you can see and on the screen of the 7Q the footage also didn't look underexposed!
 
It would be great to get some assistance here. Maybe I do something wrong, but I don't understand whats happening here!

Mitch? :)

Thanks!
 
The RAW is not underexposed, it is linear. You don't want to raise the exposure, you want to adjust the gamma curve. A linear gamma is 1.0, but standard video gamma is 2.2.
 
The RAW file itself is linear. However, unless you have selected "linear" in the RAW settings in Resolve you are not seeing the linear data. If you have selected Blackmagic Film, you are seeing the linear data with the Blackmagic film curve applied. This is a log curve, but it is not the same as the S-Log2 curve.
 
Nick_Shaw said:
The RAW file itself is linear. However, unless you have selected "linear" in the RAW settings in Resolve you are not seeing the linear data. If you have selected Blackmagic Film, you are seeing the linear data with the Blackmagic film curve applied. This is a log curve, but it is not the same as the S-Log2 curve.
Click to expand...

That's what i've done from the early days on - selected BMD film and upped the exposure in the camera raw tab to +3. So, what shall we do to get the true curve of slog2 from the linear raw file?

i suppose we should display the raw as linear (how?) and then applying a "linear -> slog2" LUT to it?

IMO, the process of BMD film, exp +3, and contrast -50 has done the best job if i compare a prores 4K recorded slog 2 file to a 4K raw recorded (slog2) file.

I doubt that this is the correct and "proper" process, though.
 
Mitch Gross said:
The RAW is not underexposed, it is linear. You don't want to raise the exposure, you want to adjust the gamma curve. A linear gamma is 1.0, but standard video gamma is 2.2.
Click to expand...

So what is the exact process in Resolve to get an accurate image and not just terrible noise? Thanks!
 
If you apply one of these LUTs in Resolve to a DNG decoded as BMD Film, you should get a good match to what the Odyssey would have recorded as S-Log2 in RAW to ProRes mode. You can then use e.g. the Odyssey preset S-Log2 to LC709A LUT in another node.

This article explains the process for working with FS7 RAW material. Most of the process is the same for the FS700, but the required LUTs are different.

I have sent these LUTs to Convergent Design, with the intent that they will be made available on their website. I am posting them here in advance of that, but be aware I have just generated them today based on the theoretical mathematical transform required. They have not yet been tested on real camera rushes, so use with caution. If anybody can do a comparison of a RAW to ProRes S-Log2 clip and a DNG RAW clip of the same image, with the appropriate LUT applied, please post here.

***IMPORTANT CORRECTION***
The FS700 in fact bakes in the EI to the RAW data, which I forgot when creating these LUTs, so the three LUTs are not strictly necessary. However, I will leave all three up there, as people may find them useful as exposure compensation LUTs. I have renamed them as "Normal", "-1" and "-2". Please re-download if you have already downloaded.
 
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Nick_Shaw said:
If you apply one of these LUTs in Resolve to a DNG decoded as BMD Film, you should get a good match to what the Odyssey would have recorded as S-Log2 in RAW to ProRes mode. You can then use e.g. the Odyssey preset S-Log2 to LC709A LUT in another node.

This article explains the process for working with FS7 RAW material. Most of the process is the same for the FS700, but the required LUTs are different.

I have sent these LUTs to Convergent Design, with the intent that they will be made available on their website. I am posting them here in advance of that, but be aware I have just generated them today based on the theoretical mathematical transform required. They have not yet been tested on real camera rushes, so use with caution. If anybody can do a comparison of a RAW to ProRes S-Log2 clip and a DNG RAW clip of the same image, with the appropriate LUT applied, please post here.

***IMPORTANT CORRECTION***
The FS700 in fact bakes in the EI to the RAW data, which I forgot when creating these LUTs, so the three LUTs are not strictly necessary. However, I will leave all three up there, as people may find them useful as exposure compensation LUTs. I have renamed them as "Normal", "-1" and "-2". Please re-download if you have already downloaded.
Click to expand...

Thanks. The LUTS seem to be great, but how do the differ from just raising exposure in the RAW tab? The Noise seems to be on the same level like when raising exposure!
So basically what the CD aarticle says; raise the exposure by +2 if you shot on ISO 2000 (which you have to on th FS700). So Mitch, what exactly do you mean by saying
'make a gamma correction'?

Thanks.


PS: are there FS 700 LUTS from CD like the one in the article for the FS7?
I'm really suprised this havn't be discussed here in the forum. Are you all shooting ProRes?
 
Fader8 said:
Thanks. The LUTS seem to be great, but how do the differ from just raising exposure in the RAW tab? The Noise seems to be on the same level like when raising exposure!
So basically what the CD aarticle says; raise the exposure by +2 if you shot on ISO 2000 (which you have to on th FS700).
Click to expand...
The LUTs are calculated to mathematically apply a Blackmagic Film to S-Log2 transform, so you get to the right start point to apply LUTs or other workflows designed for an S-Log2 input.

The LUTs included with the article were EI 500 only, to reduce the number of LUTs, so changing the exposure to +2 with an EI 500 LUT effectively gave you an EI 2000 output. With these LUTs the "Norm" LUT gives you whatever EI you shot at, because the FS700 has already baked that into the recording. The -1 and -2 LUTs give you one and two stops less. It is true you could achieve the same result with the "Norm" LUT and exposure set to -1 or -2. You would have to test to see if the two approaches gave you a discernible difference in term of noise.

PS: are there FS 700 LUTS from CD like the one in the article for the FS7?
Click to expand...
I wrote that article for CD, and created the LUTs. So these LUTs are the equivalent for the FS700 of the FS7 ones from that article. The only difference is that the range of the output of the FS7 was designed to match DPX recordings, and these FS700 ones are scaled to match ProRes recordings. I am working on ProRes matching ones for the FS7 too.
 
Fader8 said:
Thanks. The LUTS seem to be great, but how do the differ from just raising exposure in the RAW tab? The Noise seems to be on the same level like when raising exposure!
So basically what the CD aarticle says; raise the exposure by +2 if you shot on ISO 2000 (which you have to on th FS700). So Mitch, what exactly do you mean by saying
'make a gamma correction'?
Click to expand...
I mean change the gamma setting before doing anything else. Then you will see an image much closer to what you were expecting, at least contrast-wise. You will still need to make exposure adjustments.

But that's stuff to do after the fact, setting parameters in Resolve. The exposure adjustments detailed in the article are about overexposing at the camera by one or two stops, then darkening the image in post. This darkens the noise along with the rest of the image, and it also means that the information now defining the shadows has more bits available to it, increasing color accuracy and lowering the chances of banding. You do lose sensitivity and dynamic range, but you gain a cleaner image with better color fidelity.
 
nick, to sum it up:

i like to shoot "normal":
with your LUTs, we only have to set the raw files to bmdfilm in the dng codec settings tab, and after that, add your "norm" LUT on top to convert from bmdfilm gamma to slog2? your lut adds the +3 exposure automatically, so no need to edit exposure ourselves.

EDIT: just tried it, as i had to transcode something anyway. looks pretty darn good! (bmdfilm doesn't differ much from slog2 anyway.) plays nicely now with my lut arsenal :)
 
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stefanhuberfilms said:
nick, to sum it up:

i like to shoot "normal":
with your LUTs, we only have to set the raw files to bmdfilm in the dng codec settings tab, and after that, add your "norm" LUT on top to convert from bmdfilm gamma to slog2? your lut adds the +3 exposure automatically, so no need to edit exposure ourselves.
Click to expand...
Correct. My "normal" LUT converts to S-Log2 at the same exposure you shot at.
 
Great, Nick! thanks for sharing these LUTs. Did anybody already compare 7Q ProRes to RAW + LUT?
At the first look I see slight shift of green of ProRes vs magenta/red of RAW + LUT
 
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