Working with LUTs in Lightroom?

[skewcrap]

Hi everyone

Im wondering if someone could give me some tips regarding the possibilitites to work with LUTs in Adobe Lightroom.

First I should tell you why I need LUTs in Lightroom. I want to invert color negative film. I digitized several thousand color negatives with the help of a DSLR and macro lens. Now, I have the images in RAW format and I would like to process them.

The proper inversion of color negatives is a highly complex topic, and it can neither be done with Adobe Lightroom nor Adobe Photoshop. Yes I know, there is plenty of information on that topic in the web, but believe me, 90% is just incorrect. It's impossible to to do the (proper) inversion from negative to positive in Adobe Lightroom.

I have a piece of software which can do the inversion process and as an output I can get a LUT file. Basically the LUT file contains the information to get from negative RAW to positive RAW.

Now, what I would like to do is to use the RAW file and the corresponding LUT file and do further processing in Adobe Lightroom. But it's not sufficient to import one LUT and somehow convert it to a profile. I need to have one LUT file fore every RAW file, similar as the XMPs work.

Do you think there is some way to do that in Adobe Lightroom?

If not, do you think there might be a possibility to create this kind of functionality with the help of the Adobe Lightroom SDK?

Do you think there might be a chance to convert the LUT file to an XMP file? I suppose it will not work, but I don't have the technical explanation why.

If I don't find a solution I could also try to work with TIF files in Adobe Lightroom, but then file size is incrased by a factor of 6 and part of the the process would be outside lightroom.

Thanks for your help.

skewcrap

Regards

[99jon]

Have you tried using the Tone Curve?

After reversing the axis you may be able to save the settings as a preset.

[skewcrap]

As I said, the inversion can not be done with Adobe Lightroom. If you are interested in details, visit https://www.colorperfect.com/, if you like to understand the math, visit http://www.c-f-systems.com/Docs/NegativePositiveCFS-244.pdf.

Of course i will share my knowledge if someone really is interested in the topic, but the aim of this thread was to solve one specific problem of a whole set of problems.

[Rob_Cullen]

From the forums I think I understand that TBMK-

1) You cannot convert the data in a Negative raw to a Positive raw. (Your software does this? Please illustrate.)

2) You can make a Profile in ACR that reverses the tone curve and use LUTs, and then use as a Profile in Lightroom.

The Profile in Lr does not reverse the tone curve in Lr or change the Basic sliders, but it does reverse the action of many of the Basic sliders. ie. The remaining problem that no one seems to be able to answer with raw files.

! CREATE PROFILES in ACR

LUTs to Lightroom – John Beardsworth

Many conversation on this 'Reversal' topic. eg. Read here-

INVERT NEGATIVES

Your "ColorPerfect" link does not work, and the c-f-systems-PDF link is highly technical (written in 2004).

[skewcrap]

Thanks for your reply.

Sorry for the broken link, the correct one is: https://www.colorperfect.com/colorperfect.html?lang=en

Regarding 1): The "pos RAW" obviously is not a real RAW, but you can generate it from the real raw by applying maths. Therefore, it's replicable, you only have to know the parameters. Basically, you have to implement exactley what is written in the mentioned paper from 2004. Yes, I know it's quite old, but there is nothing similar out there. I googeled for hours. I read all scientific papers I could find on that topic, I read books about color science and the chemistry behind color negatives. I had contact with former Kodak scientists. I can say now, that I understand the problem and I know what you have to do to solve it and why it's really tricky. Best would be to implement everything in a Lightroom plugin. Unfortunately I don't have any experience with the Lightroom SDK.

Regarding 2): Can you do that specifically for each RAW file? Otherwise, it does not help, because the profile is different for every image.

[Rob_Cullen]

Thanks for your followup post.

Now it is way beyond my level of knowledge.

For those of us using a DSLR to 'scan' negatives as 'raw' - we live in hope that a plugin to do this inversion will eventuate.

[Jao vdL]

You should just be able to use the LUT you mention directly in Camera RAW to create a profile that you can use in Lightroom. I do think you might still have to deal with the sliders working opposite to what you expect though. Wobertc posted some links on how this works. I have used these to create film simulation profiles from LUTs I use for video work. It is not hard to do but it has some limitations.

[Jao vdL]

Here is an actual tutorial for the entire process for raw images created from color negatives: https://www.cuchara.photography/blog/2018/5/one-click-inversion-of-color-film-negatives-in-lightroom

[skewcrap]

I had a look at the various links.

Regarding the Lightroom Plugin Negative Lab Pro: I know it, but I don't trust it. I don't trust any tool without knowing exactly the math behind it. I wrote the author of the plugin some time ago, but unfortunately I never got an answer.

If I understand it correctly, Lightroom accepts CUBE files. Is there any documentation available on that? Creating one such file by hand is ok for one image, but not for thousand. I need one for each RAW file. This only works if it can be done automatically.

But once again, I repeat myself: The inversion from negative to positive can not be done with Photoshop. Read page 7 of this paper: http://www.c-f-systems.com/Docs/NegativePositiveCFS-244.pdf

The inversion process is difficult because:

-Tonal values are highly compressed. You need enough bit depths to resolve the values.  Example: if you use 12 bit you have 4096 tonal values, right?, But only 21 are available for the range of middle-gray to white of the original scene. The rest (4075 values) belongs to the range from middle-gray to black. If you don't believe me, do the math yourself.

-In a color negative the information is "stored" in 3 layers with different colours. To correctly extract this information you would actually need a sensor which is only sensitive in a small part of the spectrum. If you use a DSLR to digitize the negative (as I did), the opposite is the case. The sensor is sensitive to a wide range of the spectrum. This means, that you have some cross couplings (called "cross talk") which can not perfectly be subtracted later on. A green pixel of the sensor is not only sensitive to one layer, but will collect light from all 3 layers of the color negative.

If you use photoshop to do an inversion, you will subtract the color value of a pixel from white, which is not what needs to be done. If you do that, you can mess around with all kind of tools afterwards, but you will never get correct colours! That's why I don't even have to read tutorials on how to convert color negatives with Photoshop. It's just a waste of time!