Thread: A better way to grade Ursa Mini CinemaDNGs

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  1. #1 A better way to grade Ursa Mini CinemaDNGs 
    Member Juan Melara's Avatar
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    Hey all,

    As promised I'm back with a new tutorial. This one is especially for you people shooting CinemaDNGs. I know I mention Ursa Mini in the title, but really it works on CinemaDNGs from any camera.

    This time I show you how to bypass the not so great BMD Film Log start point when working with CinemaDNG files inside Resolve. You will get access to the full dynamic range, richer colours through out the full range and all in a curve thats a lot nicer to grade than BMD Film.

    Ursa-Mini-Comparisons-960x1200.jpg

    One issue I wasn't too sure about is how the BMD 4.6k Film V3 color space affects cinema DNGs. When shooting on newer firmware supporting the V3 space, are there extra options in the Camera Raw tab inside Resolve? Or are the CinemaDNGs identical to CinemaDNGs shot with previous firmware? I couldn't actually track down any DNGs newer than April 2016 so I'm not 100% sure.

    As always, leave any questions or feedback!
    Last edited by Juan Melara; 11-20-2017 at 08:20 AM.
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  2. #2  
    Senior Member shijan's Avatar
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    There are two different implementations of RAW input colors in Resolve:
    1. To get corrected colors from RAW you need to bypass input color space transform in project settings. it acts as ColorChecker correction and helps to get exact same colors from RAW as from ProRes. But as we can see from your example it also can make things worse in some situations.
    2. To get original sensor data without additional colors correction you need to use YRGB Color Managed. It just shows RAW data as is without any additional correction.





    And yes Cineon clips dynamic range compare to other LOG curves http://www.bmcuser.com/showthread.php?20965

    And it all can be done with one single node + ColorChecker correction to get perfect neutral starting point.
    Last edited by shijan; 11-20-2017 at 02:33 PM.
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  3. #3  
    Member Juan Melara's Avatar
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    Thanks for responding!

    Using the Resolve Color Managed (RCM) workflow is actually the same as using the Color Space Transform node (CST). Except what you gain in simplicity you lose in flexibility.

    Using the RCM - In the background the raw data is being debayered into linear and in XYZ (CIE) colour space. So as per your example, the RCM then applies the BMD 4.6k Film Curve to the linear data and transforms XYZ into BMD 4.6k Film V3. All good there.

    Using the CST - We manually select to debayer the raw into linear and into the Rec709 or P3 D60 colour space. The CST internally converts the input gamma into linear and converts the colour space into XYZ. Except since we are feeding it linear, only the colour space undergoes a transform into XYZ. Then we make our output choices. So in the example in the tutorial linear is converted into Arri LogC and the XYZ colour space is transformed into BMD 4.6k Film V3.

    The issue you will see here is that I've got one extra colour transform step over using the RCM. So it goes - Rec709 > CST internally converts to XYZ > CST converts XYZ to BMD 4.6k Film V3. Where using the RCM the process is - XYZ > RCM converts XYZ to BMD 4.6k Film v3 In researching the tutorial I found there is actually a tiny imperceptible difference between the results of the two methods (no surprise there really). But it should never impact the final result. You would need a super saturated colour that exceeds the bounds of the Rec709 colour space for it to be an issue. If that actually occurs, it's going to be an issue anyway!

    The main benefit of doing these transforms manually in the node graph is that they can adjusted on a shot by shot basis. You're not limited to a project wide setting and you're able to tailor your approach based on the shot. Sure you can always bypass it on individual shots, but then you'll most likely need to resort to the CST anyway to get back similar functionality.

    In your last example try setting the Timeline Color Space in the RCM to Arri LogC. It's gentler log curve thats easier to grade compared to BMD Film. In use I've found it requires a lot less work to retain detail in the shadows and highlights. And it allows me to arrive at a better end result with a lot less work. Plus it's compatible with any LUT or process that expects log as an input, not so with BMD Film curve, not without a bit of wrangling.
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  4. #4  
    Senior Member shijan's Avatar
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    Quote Originally Posted by Juan Melara View Post
    Using the RCM
    In your last example try setting the Timeline Color Space in the RCM to Arri LogC. It's gentler log curve thats easier to grade compared to BMD Film. In use I've found it requires a lot less work to retain detail in the shadows and highlights. And it allows me to arrive at a better end result with a lot less work. Plus it's compatible with any LUT or process that expects log as an input, not so with BMD Film curve, not without a bit of wrangling.
    Yea, i also come to the conclusion that BMDfilm log and color space is not a best setting for timeline. It just very strange and unnatural when you adjust contrast. Don't know why but Arri LogC is always feels very low contrast. Earlier use Cineon LOG (contrast Pivot 0.52) but it appears limited in some situations http://www.bmcuser.com/showthread.php?20965 so i moved to RED Log3G10 (contrast Pivot 0.38) which have same contrast response as Cineon.
    As a color Gamut i use Panasonic V-Gamut because it is the only usable color gamut to work with ColorChecker correction tool in Resolve.

    RED Wide Gamut shifts colors to purple reds when use ColorChecker correction tool (probably bug)
    ACES Gamut works very well ColorChecker correction tool but shifts colors to warm because D60 white point.
    Rec2020 is more like delivery color gamut and if you use it also adds Rec2020 metadata to exported file even if Color Space Node set to Rec709. This produce oversaturation in some video players.
    Last edited by shijan; 11-20-2017 at 08:33 PM.
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  5. #5  
    Senior Member CaptainHook's Avatar
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    Hi Juan,

    To clear up some things for you,

    The 4.6K film curve does handle the full dynamic range of the sensor, but for ISO1600 for example we store into super whites to make the most of available bit depth. You'll find some other log curves are more compressed and roll off more, but they use less code values to store the range and will max at 940 or even lower in some cases. They still can cover the full range of their sensor, but they are using less bit depth than they could to store this. Yes in our case you may have to "pull back" to get the highlights into video range, but we're using as much of the bit depth for our log curves as we can. In the example of your video you have set ISO800 which maxes at 940, but highlight recovery is on which will actually create information above that into super whites (information not recorded by the sensor but reconstructed from channels not clipped) which you see return into video range on the scopes as you pull back exposure.

    FYI your steps changing the RAW tab to 709 and linear are somewhat redundant, as you could just set the CST plugin to BMDFilm 4.6K for input (in the case of this old footage, don't use the V3 version) and transform to 4.6K Film V3 (and logC gamma if you prefer) from there.

    Something to be mindful of though is that the CST plugin will assume a white point of 6000K, so transforms starting from different white points will not be as accurate.

    Quote Originally Posted by Juan Melara View Post
    One issue I wasn't too sure about is how the BMD 4.6k Film V3 color space affects cinema DNGs. When shooting on newer firmware supporting the V3 space, are there extra options in the Camera Raw tab inside Resolve? Or are the CinemaDNGs identical to CinemaDNGs shot with previous firmware? I couldn't actually track down any DNGs newer than April 2016 so I'm not 100% sure.
    RAW footage shot over a year and a half ago like in your video will be interpreted in the old colour science, but clips shot with firmware after April 2016 have metadata identifying the clip was shot with colour science V3 so that Resolve can automatically apply the correct transforms as needed. Those clips will be displayed in BMDFilm 4.6K V3 by default.

    Quote Originally Posted by Juan Melara View Post
    Plus it's compatible with any LUT or process that expects log as an input.
    Be careful with LUTs, they often expect a specific colour space as input and may shift colours unpredictably and often further from your intention than not using the LUT - not to mention the high potential for clipping colour if the LUT assumes a wider gamut than the input actually provides. "Any LUT or process that expects log as an input" is too generic to even describe most LUTs.
    Blackmagic Design
    My BMD LUTs.

    **Any post by me prior to Aug 2014 was before i started working for Blackmagic**
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  6. #6  
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    Quote Originally Posted by Juan Melara View Post

    In your last example try setting the Timeline Color Space in the RCM to Arri LogC. It's gentler log curve thats easier to grade compared to BMD Film. In use I've found it requires a lot less work to retain detail in the shadows and highlights. And it allows me to arrive at a better end result with a lot less work. Plus it's compatible with any LUT or process that expects log as an input, not so with BMD Film curve, not without a bit of wrangling.
    The footage you're using in this demo was shot before the V3 BMD colour.

    Also, I've run into issues when colourist use the Arri LogC curve because it "expects" a certain way of performing and when you feed it footage from another camera you can have unexpected issues, especially in super saturated areas.

    JB
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  7. #7  
    Member Juan Melara's Avatar
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    Quote Originally Posted by John Brawley View Post
    The footage you're using in this demo was shot before the V3 BMD colour.

    Also, I've run into issues when colourist use the Arri LogC curve because it "expects" a certain way of performing and when you feed it footage from another camera you can have unexpected issues, especially in super saturated areas.

    JB
    Transforming into LogC shouldn't introduce any issues in colours that aren't already there in the original. It's just a gamma conversion, no different from using the curve tool to add an s-curve or inverted s-curve to the footage. There is no colour space conversion.

    Where colourists tend to get into trouble is when they start using the standard Alexa LogC to Rec709 LUT that has a colour matrix conversion built in. In the mistaken belief this will give them the Alexa look. Applying that LUT to anything other than LogC / Alexa Wide Gamut (AWG) footage is likely not going to look great. Especially when the colour space they feed into it is smaller than AWG. It's that mismatch and the fact there is no smart gamut mapping of out of gamut colours that causes the oversaturated colours.

    I also see colourists use a CST to convert into LogC/AWG, then apply the LogC to Rec709 LUT to that. That, believe it or not, can actually work. As you're feeding the LUT exactly what it expects. As long as the colour space you convert into AWG isn't larger than AWG then you likely wont have issues with saturation. And if you do exceed AWG due to creatively adding saturation, you can use the CST to gamut map them back into range - super simple. I actually do this gamut mapping all the time even with Alexa footage.

    To summarise, this conversion isn't about trying get the Alexa look, or trying to make the colours match an Alexa. The conversion into LogC is purely to get into a curve thats nicer to grade and actually works as expected when using various tools and techniques that expect a more standard log curve.
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  8. #8  
    Senior Member shijan's Avatar
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    Quote Originally Posted by Juan Melara View Post
    Transforming into LogC shouldn't introduce any issues in colours that aren't already there in the original. It's just a gamma conversion, no different from using the curve tool to add an s-curve or inverted s-curve to the footage. There is no colour space conversion.

    Where colourists tend to get into trouble is when they start using the standard Alexa LogC to Rec709 LUT that has a colour matrix conversion built in. In the mistaken belief this will give them the Alexa look. Applying that LUT to anything other than LogC / Alexa Wide Gamut (AWG) footage is likely not going to look great. Especially when the colour space they feed into it is smaller than AWG. It's that mismatch and the fact there is no smart gamut mapping of out of gamut colours that causes the oversaturated colours.

    I also see colourists use a CST to convert into LogC/AWG, then apply the LogC to Rec709 LUT to that. That, believe it or not, can actually work. As you're feeding the LUT exactly what it expects. As long as the colour space you convert into AWG isn't larger than AWG then you likely wont have issues with saturation. And if you do exceed AWG due to creatively adding saturation, you can use the CST to gamut map them back into range - super simple. I actually do this gamut mapping all the time even with Alexa footage.

    To summarise, this conversion isn't about trying get the Alexa look, or trying to make the colours match an Alexa. The conversion into LogC is purely to get into a curve thats nicer to grade and actually works as expected when using various tools and techniques that expect a more standard log curve.
    I'm not a native english speaker and complicated things sometimes hard to explain, but i try.
    I was also thinking first that things are so simple and that CST is a magic tool for any situation until start testing and compare things. It works not same as Color Management in Photoshop. CST just do a non destructive math but that math not always match visual appearance during grading. Every sensor have unique native color space and contrast response, it is like hardware level response. CST maps that data from one space to another and until you adjust contrast or color wheels or apply dedicated LUT you don't see any visual difference. Some Color Spaces and LOG curves match better one to another some match less.
    Can you can convert BMD to Alexa color space and Log gamma? - Yes
    Will you get same colors and contrast response as real Alexa footage when you start to grade it - No

    Currently it seems all we can do is just feel how different color spaces behaves during grade or simple contrast adjust compare to BMD film. For example V-Gamut produces warmer yellows, Alexa adds magenta to reds, Rec2020 boosts greens and makes cooler yellows, BMDfilm LOG works great when you need to boost expose and lower gain (probably because native sensor values are unchanged), but looks strange when you start to adjust contrast. It just all different and depends of camera source, Timeline color space and output color space.
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  9. #9  
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    Quote Originally Posted by Juan Melara View Post
    Transforming into LogC shouldn't introduce any issues in colours that aren't already there in the original. It's just a gamma conversion, no different from using the curve tool to add an s-curve or inverted s-curve to the footage. There is no colour space conversion.
    Perhaps we're talking about different things.

    The LogC LUT certainly seems to do a lot more than only change a gamma curve, but I'm not THAT familiar with how Resolve works in the pipeline of processing you're talking about which is doing a transform by other means. If you're truly talking about an actual gamma curve only ? I understood a LUT could also be doing colour transforms and indeed that's what I see going on.

    The LogC REC 709 LUT is more than just a gamma curve as I understand, and have seen in end results when applied to cameras that aren't generating Alexa LogC shots.

    JB
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    Quote Originally Posted by John Brawley View Post
    Perhaps we're talking about different things.

    The LogC LUT certainly seems to do a lot more than only change a gamma curve, but I'm not THAT familiar with how Resolve works in the pipeline of processing you're talking about which is doing a transform by other means. If you're truly talking about an actual gamma curve only ? I understood a LUT could also be doing colour transforms and indeed that's what I see going on.

    The LogC REC 709 LUT is more than just a gamma curve as I understand, and have seen in end results when applied to cameras that aren't generating Alexa LogC shots.

    JB
    Juan is talking about using the colour space transform with gamma only to arri log c, not a lut.
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