HaldCLUT creating artifacts - Please help!

Software RawTherapee
1

I use 3D Lut Creator to color/luminosity correct images. It has a built-in utility for this which corrects based on a x-rite color chart.

My process is:

  • Shoot RAW (NEF)
  • Bring into Rawtherapee and apply my base profile for this workflow, which essentially has all color correction modules turned off, including color management, etc. This is to allow 3D Lut Creator to handle all adjustments.
  • Export to Tiff. wich is necessary for 3d Lut Creator.
  • Open Tiff (with my RT base profile baked in) in 3d Lut Creator, apply correction utility, save out HaldCLUT, PNG, 64.
  • Bring back to Rawtherapee and apply HaldCLUT.
  • Export as tiff for use

Usually, this workflow is fine. But just recently I had to work on some foliage with lots of greens, and in these images using my usual workflow I’m getting some strong artifacts (blue and green artifacts in the shadows).

I’m not sure what is going wrong. Usually, this workflow is fantastic. I can see the correction is working properly in 3D Lut, and if I export a tiff from 3D Lut with the correction burnt in it comes out fine. But when I bring it back to RT I get this problem.

Any ideas? The only thing that seems to affect the artifact is changing demosaicing, but none of the different options actually get rid of it, just change it a bit.

I would love to get this fixed and working. I’m attaching:

  • Two images so you can see the problem (blue and green artifacts in the shadows)
  • The base profile I use to export the initial shot to Tiff, it’s basically everything off.
  • HaldCLUT

So, if you open the .NEF image, apply the profile then select the HaldCLUT with the film simulation module you should see the second image above with correct colors & luminosity, but also artifacts.

3dL
3dL1842×1074 483 KB
RT
RT1868×1163 885 KB
Texture Start 2020_Auto_nopro.pp3 (12.8 KB)D82_6226.NEF (45.6 MB) D82_6226-2

2

@PhilipB I’m not sure, but it may have to do with your attempt to bypass the entire ‘normal’ color pipeline. You have no input profile selected and do not apply white balance. Afaik, the purpose of a LUT is not to replace these color management steps - although maybe you can! - but only to apply a certain look to an image.

3

Also, the LUT you provide doesn’t look smooth at all. I wouldn’t be surprised if that causes the artifacts.

4

If I turn on Color Management module with auto-matched camera profile (base table enabled, but not tone curve) and also white balance before exporting my tiff I still get artifacts. See attached.

I

3
31904×1196 476 KB

5

I cannot find any of the HALDCLUT images (png or tiff) you are troubled with 
 the one supplied is a low resolution and unusable.

Although I don’t give it strong success probability 
 could you try gradually changing the working space from Prophoto to something more narrow (rec2020, AdobeRGB, sRGB ??)

6

The HALD clut you posted will cause artifacts in the shadows. Look carefully at the clut. There are 8 “columns” of colours. Wthin each column, each row should usually change smoothly. But we see there are many abrupt transitions, with pixels that are much lighter than others in the row.

Further, these lighter pixels mostly occur where the “normal” pixels are dark. So, when we apply the clut to a photo, we expect that some shadows will have strangely light pixels.

7

So it sounds like 3D Lut creator is possibly producing problematic HaldCLUTS
But Im not sure as the .cube files work as expected with other software. hummm

It will also export .3DL and .cube files. but it doesn’t look like I can use those with RT, unfortunately.

8

So I tried the HaldCLUTs in Darktable and got similar artifacts.

However, darktable also takes .cube LUT files. Generating a .cube file in 3D Lut Creator from the same correction worked perfectly! I got the expected correction with no artifacts.

Maybe HaldCLUT was not properly implemented in the software. Humm. To bad. I may have to find a .cube to HaldCLUT converter. Or switch to Darktable for now.

I requested .cube support for RT. Maybe it will show up. That would be awesome.

9

Perhaps you could try to generate a haldclut in DT.
Load an identity haldclut, apply the .cube lut, output the hald clut in png format. Use in RT.

What I cannot answer:

  • in what color space the .cube is applied in DT? is it important that it is the same as the one used to generate the .cube?
  • in what color space the Haldclut is applied in RT? is it important that it is the same as the output profile used to generate the Haldclut in DT?
1 Like
10

A quick search on the Internet reveals that both G’MIC and ImageMagick can convert .cube files to HaldCLUT.

1 Like
11

I was thinking that the issue might be that I am 1) baking out a TIFF 2) then making the correction based on that and baking out the LUT, 3) then trying to apply that LUT back to the RAW/NEF.

Perhaps there is a colorspace issue here? My working space is ProPhoto, but output profile is sRGB?

Im going to try applying the out to the TIFF I use to make the correction/LUT see if I get the artifacts.

Any thoughts here?

Annotation 2020-04-08 222151
Annotation 2020-04-08 2221511385×951 284 KB

12

nahh
didn’t work. tried to apply the LUTs to the TIFF’s swap around the colour spaces. No solutions there.