An 8bit sRGB JPG can be converted to a 16bit ProPhoto Tiff with any software. BUT there is no way to recover the data-loss from the conversion RAW to JPG.
Hi Sebbe,
And there it gets interesting.
First of all, Demosaicing Raw file data can be done in different ways, that's why we have different Raw conversion engines in the market. Otherwise, they would all use a similar, maybe DCRaw type of demosaicing. An application like RawTherapee offers a choice of algorithms, and they do produce different results (resolution/artifact trade-offs, sensitivity to noise amplification, and false-color artifacts from the more undersampled Red and Blue Bayer filtered pixels compared to the undersampled Greens).
So different Raw conversion engines will also produce somewhat different output, even in TIFFs.
Then we get additional JPEG compression losses of, mostly, Chroma precision depending on the quality settings at conversion time. And usually, there are additionally also losses due to gamut compression, going from e.g. ProPhoto RGB to RGB conversion, and additionally by going from 16-bit/channel precision to 8-b/ch precision.
By the time we have a JPEG image, it's not very suited for postprocessing anymore, and it's not very robust. JPEGs are basically an end-product for display or print. Their robustness has been sacrificed for smalle size, and artifacts are baked in.
Interestingly, by using Artificial Intelligence, it
is possible to recover from some of the losses incurred when converting to 'lossy compression' JPEGs. The loss of precision in the Chromaticity is where most of the compression is achieved, and this process
can be reversed to a certain degree. It can be done to greater precision in 16-b/ch, and also when using a wider gamut colorspace.
It won't be exact, because image fragments are replaced by the results of trained AI models. The results depends on the training sets. But then, TIFFs from Raws are also not created equal.
Sure, a reverse-engineered TIFF is not an un-demosaiced Raw, but it could be very close, or even at times better (because we have replaced pixels by credible RGB data per pixel instead of only R, or G, or B interpolations).
Cheers,
Bart
P.S. Keith Cooper has written an initial review based on an earlier beta version of the software:
http://www.northlight-images.co.uk/topaz-jpeg-to-raw-ai-review/