I will reply instead of @wojtek but with his words. He sent me an email once to explain the process
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Load a neutral LUT PNG (attached to this post) into an image editor.
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Apply the same post-processing steps that you would apply to the visualization screenshot to achieve the desired effect.
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Save the post-processed LUT as PNG and load it into Shapespark.
(You can compare this process with Unreal’s: Color Grading and the Filmic Tonemapper in Unreal Engine | Unreal Engine 5.1 Documentation )
If you use Photoshop, I think you should be able to produce a PNG LUT from one of your other-format LUTs by applying the other format LUT to the neutral LUT PNG in Photoshop (according to: Convert a CUBE or 3DL LUT to a PNG Image)
Right klick on the neutral LUT and save it as PNG