DRT / Color Space

[Abby Bader]

Hi! I need to normalize log material and I wonder if that can be done by transforming the material from one color space to another inside of Baselight or if I need / should apply a DRT. Any thoughts? Abby

[Andy Minuth]

Hi Abby,

I assume You want to do a batch conversion of some kind of log footage into a video color space.

Put the footage in a scene. Set the scene working colour space in the 'Scene Settings' to whatever kind of log flavour Your footage is. e.g. Arri LogC WideGamut, etc. If it is a film scan, I recommend ADX.

The 'Input Colour Space' can remain at 'No Conversion'. If You have different kind of log flavours, set each clip to the according camera with the 'Input Colour Space'.

Leave the 'Grade Result colour space' at 'From Stack'. 

Now change the viewing color space in the cursor to your preferred output. Usually this will be Rec.1886: 2.4 Gamma / Rec. 709

 

Because the conversion is going from a scene-referred color space (camera icon) to a display referred color space (display icon), a DRT should be applied. Which one You choose is a question of personal taste. Generally the 'ACES 1.0 (Dim surround)' is a good choice.

The ARRI Photometric is applying the same look, that an official ARRI LUT from LogC to Rec709 would do. But You can do it on any kind of camera.

'Truelight Film 1' applies a filmic look, that mimics the result of a print stock. 

'Truelight Video 1' i do not recommend for a batch conversion of footage. The idea behind this DRT is, that Telecine-style colourists, who are only used to grade in a display colour-space, are still able to benefit from some of the features of 'Truelight Colour Spaces'. They prefer a very flat image, to start their grade with, that is why this DRT is outputting a quite low contrast image, which needs some additional grading, before it looks "right".

I hope this answers Your question. Andy

Edited September 15, 2016 by Andy Minuth

[Abby Bader]

Thank you so much for your detailed explanation. If the normalization (Log --> 709) already is done by setting the working color space to Log ( Arri LogC WideGamut) and viewing space to Red 709, I don't understand why the Photometric DRT should be applied to do the exact same thing? By doing the exact same thing I mean normalizing the Log image like an official ARRI LUT would have done.

45 minutes ago, Andy Minuth said:

The ARRI Photometric is applying the same look, that an official ARRI LUT from LogC to Rec709 would do.

 

[Andy Minuth]

The DRT is about how this conversion is done. They offer different looks. When You switch between them, You will notice changes in contrast and colour. I advise against setting the DRT to 'None' in this workflow, because then the final image will not look like intended.

BTW: I forgot to add in the first post, that You have to set the render colour space according to Your cursor colour space.

[Abby Bader]

Ok great, thank you! So the normalization process going from a a logarithmic file to linear is done in the color space conversion, while the DRT's offer some chroma and contrast adjustments? 

[Andy Minuth]

Yes kind of. The DRT is needed for conversions from HDR (e.g. Log) to SDR (e.g. Rec1886). The DRT is applying a tone-mapping (usually like a S-curve in the luma channel), that tries to compress a lot of the highlights and shadows into the final image. Otherwise they would be clipped. Something comparable happens with the colours as well. 

So basically the DRTs are different approaches, of how You can display an image with a high dynamic range on a low dynamic range display in a 'pleasing' way. 

I recommend to watch this tutorial of @Daniele Siragusano, it covers this topic as well: 

Part 1

 

Part 2:

 

[Abby Bader]

You are the greatest, thank you!

When you say that the DRT is needed for conversions from HDR (e.g. Log) to SDR (e.g. Rec1886), you mean all cameras that produce logarithmic images like Alexa, RED etc? Or only needed when those cameras are set up for HDR shooting? If that is a camera setting...

[Andy Minuth]

Yes, for all cameras that are listed with a camera icon color-space (mostly log color-spaces). The camera manufacturers are using log curves to solve the problem of storing HDR images from the sensor in an efficient way.

Most cameras can also shoot in Rec.709, which means they produce a video signal, that can go on-air immediately (and is SDR). In this case, a DRT is not needed, because it got already applied inside the camera, but You are loosing latitude for the grading. 

 

[Tom Evans]

Interesting topic! Is it possible to do the normalization process inside Resolve without manually working the curves or applying a LUT? 

[Nicolas Hanson]

Don't think so...

[Andy Minuth]

On 9/17/2016 at 0:10 AM, Tom Evans said:

Interesting topic! Is it possible to do the normalization process inside Resolve without manually working the curves or applying a LUT? 

My Resolve knowledge is not up to date. I can't help You with this one, sorry.

[Stepan Kozlov]

On 9/16/2016 at 10:10 PM, Tom Evans said:

Interesting topic! Is it possible to do the normalization process inside Resolve without manually working the curves or applying a LUT? 

Pretty late answer i'm guessing but you can do this with the colourspace ofx plugin. The problem with that one though is that it is built to convert from one colourspace to another in a mathematically precise way which is not always as aesthetically pleasing like it would be if with a DRT. For example you might convert from logc to rec709 and find that the highlights are clilpped and look awful. The data is still there and you can recover them but it's not as pleasing of a conversion as the arri lut that resolve is supplied with. 

[Tom Evans]

Thank you very much!

[Thomas Singh]

Wishlist for DR15

[Soumitra Sarkar]

All above description are very much helpfull to me. I am little bit confused about the scene setting when I grade in ACES workflow.Is there need to set all the multiple camera and DPX clips " Imput colour space" setting manually. And what is DRT setting in multiple camera footage. 

I actually want to know what is the setting of ACES workflow in the time of grading multiple camera footage. And what is setting of "IRT" in the time of multiple type of Delivery. Basically I didn't see exacat same output in mobile display which I have grade in DCI P3/2.6 colours space. Basically I did,  P3 colour space grading material offset in Rec709 1886 timeline and render in prorec file.But I think all the mobile display and monitor are in SRGB colours space.How I solved it. 

Plz help me

[Tom Tomlinson]

On 9/15/2016 at 5:19 AM, Andy Minuth said:

Put the footage in a scene. Set the scene working colour space in the 'Scene Settings' to whatever kind of log flavour Your footage is. e.g. Arri LogC WideGamut, etc. If it is a film scan, I recommend ADX.

Was just curious about your choice of ADX over something like traditional cineon log. How many scanners out there can actually or are doing ADX scans?

[Andy Minuth]

On 10/11/2017 at 5:02 AM, Tom Tomlinson said:

Was just curious about your choice of ADX over something like traditional cineon log. How many scanners out there can actually or are doing ADX scans?

Film scans are not in a RGB color space but defined in printing densities. The conversion between those worlds was handled by the print emulation lut. But when You want to convert film scans into an RGB space to apply a DRT You need a formula representation of film - which is ADX.

So basically You can put Cineon scans in the timeline and tag them as ADX. You don't need to change Your scanner settings.

Also please note that information from the Baselight release notes:

  FilmLight: Printing Density Log / ~ADX Colour Space
  ---------------------------------------------------

  This colour space is similar to the Academy "ADX" colour space but
  with more focus on robustness and invertibility. It is designed as
  connection space for the Truelight Film 1 DRT, and should not be
  used as grading colour space for digital content. However if your
  footage is primarily camera negative log scans you can use this
  space as Input and Working Colour Space in combination with the
  Truelight Film 1 DRT.

 

[Tom Tomlinson]

Thanks for the reply Andy. 

It was my understanding from talking to some of the scanner manufacturers that they were working on that feature where the machine could do that. The only machine /company that gave me their procedure/workflow was Arri. DFT (as of February) is working on it.

[Abby Bader]

Can you elaborate more on the Arri workflow @Tom Tomlinson?

[Tom Tomlinson]

This is the info I got from Arri support--

I would recommend involving them right away.

This may also involve getting a test roll of film from arri to verify your scans.

I was given this info 3 years ago--maybe its been updated.

Output Academy Printing Density.pdf

[Emily Haine]

 

On 1/26/2017 at 4:12 PM, Stepan Kozlov said:

Pretty late answer i'm guessing but you can do this with the colourspace ofx plugin. The problem with that one though is that it is built to convert from one colourspace to another in a mathematically precise way which is not always as aesthetically pleasing like it would be if with a DRT. For example you might convert from logc to rec709 and find that the highlights are clilpped and look awful. The data is still there and you can recover them but it's not as pleasing of a conversion as the arri lut that resolve is supplied with. 

Very useful information. Does any of you have any experience with the colourspace OFX plugin for this kind of use?

[Jussi Rovanperä]

In Resolve 14 the color space transform ResolveFx has now tone mapping and gamut mapping options. I've been using the transform nodes a lot, for example converting slog2 to log-c in the first node, and then converting log-c to rec709 with the tone mapping in a later node.

The same could be done with using "Resolve YRGB color managed" and setting input to slog2, timeline to log-c, and output to rec709 with tone mapping enabled. 

[Amada Daro]

On 15.9.2016 at 11:19 AM, Andy Minuth said:

The ARRI Photometric is applying the same look, that an official ARRI LUT from LogC to Rec709 would do. But You can do it on any kind of camera.

'Truelight Film 1' applies a filmic look, that mimics the result of a print stock. 

Hi @Andy Minuth and thank you for the explanation.

Does the ARRI Photometric DRT eliminate the need of the regular LogC to Rec709 LUT provided by ARRI?

Does the Truelight Film 1 LUT mimic the film stocks precisely?

You wrote that the DRT output the image a bit flat. Does that mean it will only transform the image 'halfway' to the IRE range known as within the REC709 standard?

[dermot.shane]

there is no "precisley matching" a film stock, too many variables in lab tollerance for any match to be more than lab X on day X at best

shoot a test, cut the camera roll, send it to three labs and the resualts are three densities, send it again a week later and there will be three more densities.... rinse and repete....

and they are all going to be within lab tollerance....

 

 

[Andy Minuth]

Hi Amada,

> Does the ARRI Photometric DRT eliminate the need of the regular LogC to Rec709 LUT provided by ARRI?

Yes exaclty. The transform from that LUT is inside the DRT, but in a more generic way, so it can be applied to and from different colour spaces.

> Does the Truelight Film 1 LUT mimic the film stocks precisely?

See dermots answer. It is based on real measurements taken from a print stock and not "graded" to look like film. But it is not intended to be used as an accurate simulation of a film-out, that should be provided by the lab doing the film-out. 

> You wrote that the DRT output the image a bit flat. Does that mean it will only transform the image 'halfway' to the IRE range known as within the REC709 standard?

The 'flat' comment was only regading the 'Truelight Video 1' DRT. There we are going to Rec.1886/709, but we are letting the colorist add the last bit of contrast manually. 

I hope that helps