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Enthusiast
Posts: 6
Registered: ‎10-25-2016
Message 1 of 11 (1,071 Views)
Accepted Solution

S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hi there,

 

I recently shot nightime footage on profile PP7 (S-Log2) on the A7S2.

 

The *.mp4 file looks correctly exposed, however when I transcode the file to Prores422 HQ in Catalyst Prepare the files become very underexposed. It only happens with footage shot in S-Log2 my other footage shot in profile PP2 during the day shows no exposure shift.

 

I have experimented selecting Rec709 vs S-Log2 as the output colorspace but there is no difference. 

 

Some file info that may be useful:

MEDIA

Format - XAVC S

 

VIDEO

Codec - AVC Long

Profile and Level - High@L5.1

Color sampling YCbCr 4:2:0 8bit

 

ACQUISITION METADATA

Recording mode - Normal

Cache rec - No

Capture gamma equation - S-Log2

 

Appreciate any help anyone can be.

 

Cheers

 

Moderator
Posts: 126
Registered: ‎02-20-2015
Message 2 of 11 (1,068 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hi timbathurst01,

 

Thank you for the post.  A couple of questions.

 

1). Are you applying any kinds of color modifications on your S-log2 footage that you are not applying to your PP2 footage?  

2). What viewer are you using to view your transcoded ProRes files in?

 

Thank you,

Omar

Enthusiast
Posts: 6
Registered: ‎10-25-2016
Message 3 of 11 (1,064 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hi Omar,

 

Thanks for your quick reply!

 

1) I borrowed the camera from a friend so don't have access to see the imidiate settings, however I know PP2 was customized by him and I'm pretty sure he wouldn't have shanged anything in PP7 yet, the camera is new to him and I'm pretty sure I'm the first to have shot in LOG. I will check though.

2) I'm using Quicktime

 

Cheers

Tim

Moderator
Posts: 126
Registered: ‎02-20-2015
Message 4 of 11 (1,062 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Thanks for the info Tim!

 

It is definitely possible that the culprit here is Quicktime, as Quicktime has had a notorious gamma shift with Prores files for years now.  Can you check those same transcoded Pro-Res files in Catalyst Prepare and see if they look correct in Prepare?  You could also check them in the editor you are using to see if the gamma shift also appears there as well.  Chances are it will only show up in Quicktime.

 

Let me know!

Omar

Enthusiast
Posts: 6
Registered: ‎10-25-2016
Message 5 of 11 (1,053 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Unfortunately I think Quicktime is off the hook on this one.

 

When I view the file in Catalyst Prepare it plays underexposed off the original *.mp4 file, so it seems the transcode process to Prores isn't causing the exposure shift.

 

(I put the Prores file into Avid and it's underexposed there also, I can't import the native *.mp4 into Avid without error messages it needs conversion first)

 

When I scroll through the files in Finder the difference is visible between the two, when I hit spacebar to preview the files in Finder the difference is visible still and I also did a test in VLC which played the original *.mp4 correctly and the prores underexposed. It appears something is happening when Catalyst first interprets the files.

 

The difference is huge I wish I could attach an example screen grab for you. I'm hoping this is something that hasn't been baked in but I have hope as it's only Catalyst that's displaying the RAW footage in a different way. Fingers crossed.

 

Thanks for looking into this Omar.

Moderator
Posts: 126
Registered: ‎02-20-2015
Message 6 of 11 (1,046 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hey Tim,

 

Thanks for the info.  So if I understand correctly, it seems the original .mp4 file looks fine in Finder and in VLC, but is looking underexposed in Prepare, is that correct?

 

What happens if, when you have the original .mp4 clip selected in Prepare, go to the Edit tab, choose "Adjust color" and then choose "Reset" at the bottom right?

 

Would it be possible for you to upload a sample clip to an FTP site such as Google drive or Dropbox so that I can download it and test on my QA machine?

 

Also, what version pf Prepare are you using?

 

Thanks Tim!

Omar

Enthusiast
Posts: 6
Registered: ‎10-25-2016
Message 7 of 11 (1,036 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hey Omar,

 

That's correct the original *.mp4 looks fine and becomes underexposed once opened in Prepare.

 

Unfortunately no change when hitting "reset" on the files within the Edit tab.

 

I have uploaded x2 sample clips for you to review on Google Drive.

 

I'm on the latest version of prepare v2016.2.0.320 (Trial version)

 

Cheers

Tim

Moderator
Posts: 126
Registered: ‎02-20-2015
Message 8 of 11 (1,030 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hey Tim,

Thanks for providing the footage! I think I have identified the problem. The issue seems to occur due to the max ISO setting in Catalyst Prepare being 10000 ISO. It seems both clips provided go well above that. One is 20000, and the other is 25600. Since Prepare is not able to match that high of an ISO setting, it is defaulting to 800 and therefore appearing much darker. If you raise the ISO bar up to 10000, it will start to more match the original clip. You can then use the tone curve to raise the exposure even more to better match the original.

Meanwhile, I am going to check with our engineers to see what we can do to fix this.

I'll let you know as soon as possible what we come up with.

Thanks Tim!
Enthusiast
Posts: 6
Registered: ‎10-25-2016
Message 9 of 11 (1,024 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

Hi Omar,

 

Great that makes sense, OK glad the footage is safe and it's a software issue. Yes I had to push the ISO a lot on this one but I must say I was surprised by how little noise there was when doing so, great camera.

 

Hopefully the engineers can work up a fix before I start editng, if not i'll do as you mentioned. One last question on the tone curve, should i pull from the middle to lift the exposure or from the top right hand corner to best hold the integrity of the image? Is there a science to that grid to know when to stop or do I just eyeball it?

 

Cheers

Tim

Moderator
Posts: 126
Registered: ‎02-20-2015
Message 10 of 11 (1,016 Views)

Re: S-log2 *.mp4 transcoded to Prores *.mov becomes underexposed

[ Edited ]

Hi Tim,

 

Thank you for your patience!

 

 Our engineers have confirmed that this is indeed a bug, so we will look into fixing it.  

 

Meanwhile, the tone curve and ISO slider should do the trick.  When adjusting the tone curve, the portion of the curve to adjust largely depends on the attributes of the image.  Dragging the top of the slider alone will affect mostly the highlights, whereas dragging the middle will mostly affect the mid tones.  For images that are dark but have bright highlights, such as a dark scene with a bright candle, it would probably make more sense to adjust the middle of the curve so as not to affect the highlight fidelity of the candle.  Conversley, scenes that are dark all around would probably be better suited for adjustments to the top of the curve.

 

I typically use the histogram to know when to stop pulling the curve, as it will tell you if/when you have any clipping and therefore is the most accurate way to judge.  However, the eyeball method can work well too if that is your preferred method.  A combination of both methods can be quite common.

 

I went ahead and created a tone curve in Prepare for you in the form of a preset that, if applied to clip C0022, should match the brithness of the original .mp4 image fairly well.  I also added just a touch of color correction in the form of an ASC-CDL to get it as close to the original as possible as well.  Feel free to download both of them at the link below and apply them to clip C0022.

 

https://sonycreativesoftware.sharefile.com/d-sffecbb5c029431d8

 

Of course, feel free to adjust to your liking.

 

Hope this helps!

Omar

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