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Help! Advice needed on creating LUTs

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I used 'Infer LUT' to create a collection of Fuji film sims. This appeared to work very well, and they do work well. Except they slow Affinity to a total crawl. I experimented with loading them to ON1 - and promptly slowed ON1 to a crawl on the LUT filter too. This led to the light dawning there might be something up with my LUTs rather than Affinity! 😂 (Who'da thunk it?? 🤔)

And the answer is staring me in the face. When I explore various LUTs I have lying around, a typical filesize is around 860k. My own "masterpieces" however come in at a solid 52,745kb a piece. <gulp>. No wonder Affinity chokes when I try and browse them!

What am I doing/have I done wrong? I'm a complete beginner at this kind of thing (and there was me thinking I was so clever...... 🙄). As I recall (and I've slept since then) I did a neutral develop of a photo with a lot of colour and tone. Then I used C1 to load the same RAW file and tried to match it by eye to the one I developed in Affinity. And then applied the Fuji LUTs one by one, exported them as TIFs (I think) and loaded the C1 Tif into Affinity as a layer above the developed RAW to infer the LUT between them, saving the result. With (which I didn't notice, obviously) the resulting massive .CUBE file. (I may not have remember the process completely correctly, but maybe enough for someone to be able to say "You muppet! Doing xx is why the files are so large."

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You may be exporting your LUTs from AP at a very high resolution, which might be necessary if the LUT does some really wild mapping, but is usually not necessary for many milder applications.  In the Export LUT dialog, turn the LUT resolution ("Quality") down to something reasonable - try a smallish resolution first to see if it is sufficient to make your images look the way you want without causing banding or other artifacts.  If you need to increase the resolution to address artifacts, do it in reasonable increments until you see the artifacts go away.

For example, I made a LUT in AP, based on a white balance and a curves adjustment, and exported it at 17x17x17 and again at 34x34x34.  The 17x LUT was about 135kB, the 34x LUT was about 1.1 MB, or about 2^3 or 8 times larger, as you would expect.  Think of the LUT as a cube of color - if you double each edge of the cube, its volume increases eight-fold (two cubed).

Also, remember that LUTs are not color space aware, so if you are using, for example, an sRGB document or working color space in AP as the basis for making the LUT, the transform contained in the LUT will only really be accurate (give you what you expect) for transforming images that are in the color space for which the LUT was constructed (ie, sRGB).




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You can also spend hours going down the rabbit hole of film sims by using infer LUT in AP with the help of the Raw Therapee film sim collection.  The collection is based on a HALD CLUT image (a synthetic image of a wide range or color, used as a reference) and the altered HALD images with each film sim applied to them.  You use them in AP by implying the Infer LUT operation just as you have done - the reference HALD CLUT image is loaded first and then the altered HALD film sim image is loaded.  AP infers the LUT and applies the film sim for that HALD image.


Have fun!


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