Purple tint when using AI Denoise on underexposed Fujifilm raw/raf (X-H2) files

[efterbilder]

Hiho,

I was playing around with raw files from DPReviews exposure latitude tool (link) and noticed that when correcting for the - 5EV underexposure by pushing the same amount in Lightroom and then running AI denoise on the file the resulting DNG has a purple tint not seen in the original file. Settings for AI denoise doesnt matter, I tried 5, 10 and 20.

As I can't seem to attach the raw file it can be obtained by selecting the Fujifilm X-H2 as camera in the link and then changing the exposure to -5EV.

Is this expected behavior consider the circumstances with the raw file being severly underexposed or is it something that might need looking into?

For reference doing the same thing with a -5EV file from the Panasonic S1 doesn't result in any tint.

[GoldingD]

On my ipad, I see no difference.

Do you have a monitor profile issue?

P.S. it would be helpful if you use the Insert Photo button instead of the Attachment button. That way the two images would be visible without having to open them separately, and would be visible side by side .

[efterbilder]

Hi,

I can't find a way to update my original post but here's the before superimposed on the after.

The difference in tone is only there because I ran denoise, I've made no other adjustments.

//Regards

[GoldingD]

Better.

Not seeing the purple.

[efterbilder]

Yeah, it's more of a blue and a bit more subtle side by side but you can definitely see the difference if you look at the left side of the image.

I just find it weird that I get this difference after denoise with RAF files and not the other ones I've tried. 

[efterbilder]

Thanks for taking the time to reply btw. 

[johnrellis]

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Here's the difference between the two exported JPEGs as shown in Photoshop -- it's significant:

[johnrellis]

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I downloaded the sample Fujifilm X-H2 and applied the default Denoise settings to it, with no Develop settings applied. There's a small difference between the original and the output .dng:

(Open the screenshot to full size to see the differences more clearly on a calibrated display.)

As you might expect, applying Exposure +5 to both images magnifies that difference, as shown in the previous screenshot.

Doing the same steps with the sample Canon EOS R6 II shows similar differences, though in the greens rather than the blues.  Here's the difference between the original and denoised:

And here's the difference after applying Exposure +5 to the original and denoised:

I don't know what in the Denoise algorithm accounts for these differences. I don't think it's noticeable with most photos, in which you're applying much smaller adjustments to the tone curves.

[GoldingD]

by pushing the same amount in Lightroom and then running AI denoise 

One thing to keep in mind. Many edits you might make prior to using AI Denoise might be ignored, or might require a new edit. Try running AI Denise before any Develop edits.