Some images preview and in basic process appear desaturated

Loving ART 1.4.1 so far, thank you Alberto.

Today some images randomly on clicking from browser or film strip, appear to be desaturated, as if ‘neutral’ processing was selected. No other processing done, straight from opening. Using bundled “Noise Reduction Low” profile.

Preview or open same image in RT 5.8 and all is exactly the same as the other nearby images. Canon 6D Mk II, .CR2 files. The tone curve in RT and ART appear quite different.

Image just opened in RT 5.8:

And in ART 1.4.1:

I tried closing down, deleting the ARP file, restart and return to the folder and exactly the same. Has anyone seen this behaviour?

Many thanks


Hi, the auto-matched curve in art uses a slightly different logic, it was changed to better deal with some corner cases. I guess it doesn’t work so well here though :frowning:
Would you be able to share a raw file that shows the problem? Thanks!

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Thanks for the reply. Sure:

In the zip, file 0333 displays the desaturation, file 0344 is very similar in colours, just minutes later, and doesn’t display the problem.

Meantime I can workaround by copying the tone curve from a ‘good’ file and applying it to the ‘bad files’.

Thanks for your help.


Hello, the tone curve of 0333 looks a bit strange in the shadows part. Copying the tone curve of 0344 to 0333 delivers a correct image. Applying a curve ‘by hand’ works as well.

As Alberto said, the auto-algorithm didn’t do its job like it should do.

All auto-buttons in photo software have one thing in common: they don’t always auto-work. QED ! :wink:

Yep, nothing is perfetc :slight_smile: I was just surprised that some very similar images came out so differently. Also, in RT 5.8 that they all came out OK. All were taken as RAW only, no camera JPGs but I’ve never seen that kind of curve from a native JPG either.

If Alberto prefers to keep the current logic I can fall back on copying a curve from one of the good frames or revert to RT if need be.

I wonder if anyone else has seen a similar effect or if the lighting/colours yesterday were just in the wrong combo for the current logic to cope with.

Yes I have had a few images like that, using the auto match tone curve. Sometimes the lowest few points in the shadow section of the tone curve look too high, so it makes the image lack contrast and saturation. But it is only occasionally…
I will try and dig an example out if it helps…

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I agree this is a bug. No auto thing is perfect but the result here is not pleasant, I’ll see if I can do something about it…

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Thanks Alberto, ART is a great tool - I appreciate the amount of work you have put in, so thank you.

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Here is an example of a file that gets tripped up by the auto tone curve matching, if it helps.
Here is the jpg thumbnail in the inspector:

Here is the preview of the raw file using auto matched tone curve:

Here is what the auto match tone curve looks like

Other similar images in the series have a similar issue, although I have picked the worst one here.

Here is the raw file.
TTR205 19.RW2 (14.7 MB)

The picture is of some soap being made, in case you were wondering what it was.

The auto matching generally works well, in my experience it is more likely to be tripped up by photos where there are very few dark / near black tones.

I haven’t tried it in RawTherapee - I am trying to move towards learning to use one piece of raw processing software rather than half a dozen, and continually comparing them…

Hope this helps, and thanks for all your work…