How to (re)compose 4 color channels?

Processing
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In another thread, dealing with the present state of decompressing X-Pro2/X-T2 RAF files, I showed what can be done using libRaw. The fastest method, so far, was to run the compressed RAF file through libRaw’s 4channels command. (You will find it in samples.)

In just 3.1 seconds, it splits up the compressed source into four .tiff files, one for each color channel (R, G, B, G2); each having a size of 12.2 Megs.

Question: what would be the best/fastest way to (re)compose these four color channels into something that would be useful in RT/DT/The Gimp?

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Splitting the raw file into Bayer channels won’t help you at all. You still need to put them back together to demosaic them.

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What about the second part of the question, the fastest way? Add G and G2, multiply each of the 3 resulting channels with scaling factor, assign 3 mono channels to r,g,b, done. Would be reduced resolution, but fast, or do I miss something?

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Yes, that would probably work.

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DeepSkyStacker does this in it’s “super-pixel” mode. Technical Info

I really like the idea behind that reconstruction method. It seems simple enough to be surprised it’s not already available in RT!

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That “super pixel” thing sounds bogus as they are comparing apples and oranges. When scaling down the properly demosaiced image to a quarter size it will be sharper, too.

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I don’t think super pixel is necessary a “bad” algorithm… it takes each non slidable 2x2 RGBG group as if a single larger color pixel, and that’s the end of the story. No apples. No oranges.

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@houz

Ach… Please do not spoil my joy after finally having managed to produce something understandable from a compressed RAF in just 3.1 seconds!

But, on the other hand: of course I would appreciate all ideas and suggestions on how to convert a compressed RAF into something useable for RT/DT/The Gimp.

Hmmm… What would be the easiest/fastest? Compressed RAF → libRaw → Uncompressed RAF?

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The source code to uncompress the compressed RAF files in libRaw has been released to public.
I know @heckflosse has started to implement this in RT, but it seems quite a lot of work and it’s not in the priorit list, t least not until RT 5 is released, I think.

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RT 5.1, I think :cry:

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Yes, I already started, but currently there’s too much work because of the upcoming rt5 release.

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Well if you want an adventure, you can reassemble those layers using ImageMagick/GraphicsMagick into a DNG file, copy over the needed metadata from the original compressed file into this new DNG, then if RT/DT can demosaic that pattern you’re in the clear. For an example how to make a DNG, see here.