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Author Topic: RED color science  (Read 6038 times)
fredjeang2
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« on: March 19, 2013, 07:17:42 AM »
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Here is what happens

1- Some Red footage has been pre-graded on set with RCX. They used a bunch of custom looks saved as a RMD files.

2- I AMA the Red files in the editor and the custom looks are effectively applied automatically so I can see the clips colored as the dp's did in RCX, I can see the custom names, the color spaces (red color 1 2 and 3), the gamma etc etc...

3- Instead of cutting directly the R3D, I choose to use a DNxHD 36 workflow as it's big volume, and make my edit. All fine.

4- Plans have been changed. Originally, the footage would have been sent to Nucoda but the prod decided that it has to be finally graded and finish in HD within the editor for costs reasons and also, that the custom presets used on set aren't valid anymore and a completly different look has to be applied, but they didn't send any alternative RMDs.  In short, we restart from zero in what color is concerned and have to color-finish in Avid. Fine, yeah...no roundtripping.

5- I conform within the editor relinking the DNxHD edit to the source material

6- My plan consists now in desapply the R3D looks done in RCX on set without using RCX to recover the flat images and therefore starting with the max DR to color correct in the editor in RGB mode. I do this cancel from the editor.

And this is where I have the question:
What I do is this: to revert to the flat file, basically I say to Avid: "no, this look isn't suitable anymore. I want you to apply
-Color Space: REDspace or camera RGB
-and for Gamma Curve I choose: REDlog film.
Avid obeys like a little dog. It works fine. All the timeline is now as flat as Jane Birkin's breast.

The only problem is that it works but I don't do that from real knowledge but from logic-intuition.
I could for example revert to camera metadatas settings, but it doesn't give me flat files to work with but a Scurved look. I don't really get this "camera metadatas settings" option and why it's not flat. Why don't they shoot flat in-camera? if everything will be color corrected? Are there really people who shoot documentary-news with RED cameras?

In terms of color space and gamma curves, the options availables in the editor are those:

Color Space: RedColor 1, 2 and 3 / Rec 709 (no because I will CC in RGB) /sRGB / Adobe 1998 /Redspace/camera RGB
I really do not get what are those Redcolor 1,2,3. Yes it changes but slightly, for example the differences between RedColor 2 and 3 are subtle, perfectly visible in curves.
And what the hell is this REDspace? Camera RGB is the less saturated.

I do not master this Red science enough to really understand what is involved behind the scene. The thing I'm doing is to choose the flatest possible look for grading trusting my eyes and the curves just by tricking options.  

Then, in terms of Gamma curve, here it is more simple because to revert to flat I obviously have to Log them but...there are 2 options:
-REDlog film
-and REDlog.

 Huh

The flattest to my eyes being REDlog film so I simply choose REDlog film, but again, I choose it because of the result I see, not because I know about it. Why co-exist those 2 REDlog flavors? Why not just REDlog film to have the widest DR?
What I'm seeing in Avid is that REDlog film is driving more towards the shadows while REDlog towards the Highlights, but that with REDlog film the work on the HL is easier because they clip later.
In fact, maybe REDlog film isn't flatter as REDlog, it just seems to be distribuited diferently and looks flatter but isn't.(?)

The same with REDcolors, why 3 flavors? and what is the guide to choose the right one?

If some Red users could share their experiences on that it would be great.




« Last Edit: March 23, 2013, 04:35:38 PM by fredjeang2 » Logged
UlfKrentz
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« Reply #1 on: March 19, 2013, 05:36:37 PM »
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Hi Fred,

first, welcome back :-) You are probably far more experienced in post processing then I am. As far as I know it makes no difference to the RED raw file that is recorded whatever you apply in camera, e.g. ISO and Color Temperature and Color Space. These are all meta data and dont effect the recorded file in any way. This meta data is "applied" to the look on the camera display to give a preview to the camera-operator / client on set. We found Redcolor3 works good for us, it is a good neutral starting point, we never alter these settings but get the look as close as we can by filtering on the lens or geling the lights when needed. Im not familiar with Avid, if you can directly work the raw files it will probably make no difference where to start from, Id suggest to choose a combination that is closest to the desired look you like to achieve. Hope this helps,

Cheers, Ulf
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fredjeang2
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« Reply #2 on: March 19, 2013, 06:31:29 PM »
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Thanks Ulf,

Ok, reading you, now I understand why the "camera metadatas settings" was giving me a curved look and not flat. It's for the preview on set you're talking about to avoid to display the flat look. That makes all sense so the client is not having a heart attack.

Cheers.
« Last Edit: May 28, 2013, 05:13:16 PM by fredjeang2 » Logged
smthopr
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« Reply #3 on: March 21, 2013, 08:17:32 AM »
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If you're going to grade in avid, at some point you need to set the parameters on the raw converter. I would set the color space to red color 3 and the gamma to red gamma 2. Set the iso and color temp to that used when the image was captured.

This should result in a video file that has not clipped any image data.

Grade from this.

Avoid red log. It doesn't buy you anything. I've tested this. And it's more confusing to grade withou proper grading software .
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fredjeang2
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« Reply #4 on: March 21, 2013, 10:26:07 AM »
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Thanks Bruce.

That's what I wanted, start from a Red file that has not destroyed recorded image datas. Thanks for the tip. Ps: agree with Red gamma 2, it gives me the best compromise. the 3 is too narrowed for my taste and the 1 looses too much details in the upper HH.

Redspace is a mystery to me. I don't get it. It's absolutly brutal in cliiping infos in the HH.

The Redlog step idea, yes, although unecessary in this particular situation, resulted to me interesting in the sense that it gives me visually a custom LUT starting point to visualize, but
it's not gona be a 3D LUT in Avid but a 1D homemade S-curving. However, as I was not sure (and now you gave me the answer) what was-were the settings that was-were preserving the entire image data in the Red files, I thought that maybe it could be the safiest route.


« Last Edit: May 28, 2013, 05:14:03 PM by fredjeang2 » Logged
Chris Barrett
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« Reply #5 on: March 21, 2013, 04:43:51 PM »
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For color space, def stick with RC2 or RC3.  Rc2 was the standard for quite a while.  RC3 was produced as an attempt to compete with Alexa in producing more pleasing, punchy colors right out of the can with good skin tone.  Try both, but RC3 is usually nicer.

I start all my grades in Resolve at RedColor 3 / RedLogFilm and throw out the metadata.  RedGamma 3 has nice contrast but clips too much, IMO.  RedGamma 2 & RedColor 3 is a decent workflow that I often use for dailies, but you can really get so much more information out of RedLogFilm if you're doing any serious grading.

To summarize:

ColorSpace:  Use RC3
Gamma:  Use RG2 or RG3 if you don't have the chance to grade.  Only use RG3 if your DP controlled contrast well.  RedLogFilm gives me the best results every time, but then you know how much I like to work my images.

Wink

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fredjeang2
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« Reply #6 on: March 21, 2013, 07:03:51 PM »
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Thanks for the imput Chris.

Do you know where (or if) there is in internet a comprehensive and visual tutos well documented on Red color science?

I don't really have to do it as I'm not going to base my workflow on Red but I can't just know a part of it and stay vaguely ignorant in others. I think it's not working that way so
I really want to go deep into the Red footage world and being able to take decisions from knowledge.

Cheers. 
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smthopr
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« Reply #7 on: March 22, 2013, 02:19:58 AM »
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Red space is "red color 1". Pretty strange. If you look at your waveform monitor using red log you'll see that half of your data bucket is unused. So it's like grading in 8 bit. If you don't have a reverse log LUT, you won't get an accurate image from a gamma adjustment. Stick with red gamma 2 in my opinion.

As for information about red color science, there's really only opinions on the net. Like mine:)

Unfortunately red color science still needs a bit of work, and there's nothing you can do about it except shooting with an Alexa...
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Bruce Alan Greene
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fredjeang2
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« Reply #8 on: March 22, 2013, 09:51:03 AM »
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Yes Bruce, this is what I noticed on the scope about redlog.


« Last Edit: May 28, 2013, 05:14:28 PM by fredjeang2 » Logged
smthopr
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« Reply #9 on: March 22, 2013, 01:33:40 PM »
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Fred, I'm not sure how to answer withou writing a few chapters.

Read carefully what mike wrote. Log is really a compression format, but Red camera RAW is not log and uses a different compression strategy. When you uncompress the red raw there's little reason to recompress into log. There is not enough dynamic range in the file to take advantage or this approach.

The conversion of the raw to rec709 in redcinex is a conversion from linear raw to video space. It's not a linear representation. It's a low contrast version of your image that retains all the image data. And most importantly, it comes close to filling the data bucket. So little or no banding artifacts will emerge when grading.

More importantly for you, you will not need to de-log the image! You really want a dedicated color grading ap to do this.  I graded a major feature film in srgb space (not log) as I've described earlier and there are no banding artifacts and no loss of highlight or shadow detail.

Right now I'm shooting a feature on Alexa to log c prores.  Not sure yet if we'll grade in log or not. The log recording is helpful here as its a 10 bit recording. The log here is a compression strategy. It would be better to record 16 bit linear, but its not possible.

I hope this is helpful and not even more confusing.
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fredjeang2
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« Reply #10 on: March 22, 2013, 01:54:09 PM »
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Fred, I'm not sure how to answer withou writing a few chapters.

Read carefully what mike wrote. Log is really a compression format, but Red camera RAW is not log and uses a different compression strategy. When you uncompress the red raw there's little reason to recompress into log. There is not enough dynamic range in the file to take advantage or this approach.

The conversion of the raw to rec709 in redcinex is a conversion from linear raw to video space. It's not a linear representation. It's a low contrast version of your image that retains all the image data. And most importantly, it comes close to filling the data bucket. So little or no banding artifacts will emerge when grading.

More importantly for you, you will not need to de-log the image! You really want a dedicated color grading ap to do this.  I graded a major feature film in srgb space (not log) as I've described earlier and there are no banding artifacts and no loss of highlight or shadow detail.

Right now I'm shooting a feature on Alexa to log c prores.  Not sure yet if we'll grade in log or not. The log recording is helpful here as its a 10 bit recording. The log here is a compression strategy. It would be better to record 16 bit linear, but its not possible.

I hope this is helpful and not even more confusing.

No, not confusing at all.  Good points.
Thankfull for that.

« Last Edit: May 28, 2013, 05:15:19 PM by fredjeang2 » Logged
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