Saved Image Artifacts

I’m using Rawtherapee 5.8
On Mac 10.12.6

I was editing the playraw file found on pixls at this link:

Saving the file produced the following results:
pre-dawn-sun-boat-IMG_1598.CR2.pp3 (11.6 KB)

As shown, it occurs on two different file types (jpeg and png 8 bit) at two different resizes (2048w and 1024w). jpeg settings were quality: 90, subsampling: best quality

Not sure if it is related to this artifact, which can be seen at 100% viewing the rocks whilst editing:

Those white spots look like clipping indicator spots, but clipping indicator is turned off. Turning various modules off can remove some of the spots. Turning local contrast or ciecam02 off gets rid of them completely.

Is this still an issue for you? Including in the nightly dev?

Just a thought. On the exposure tab, under the exposure settings, is the “Clip out-of-gamut colours” box checked or unchecked?

Yes, but I’m not devastated by it. This is not my image, and its the only image I’ve seen it happen on. Not trying the nightly dev on my old mac.

It was checked, however I have just tried an export unchecked and the same issue occurred.

Sorry for replying an old thread, but (I think) I found out what have caused this. The primary cause is the resize tool. Disable it (or use nearest algorithm) and most of the artifacts are gone. The secondary cause is the color curve in CIECAM02. Turn it back to linear will eliminate the remaining artifacts.

Good find, it was the ciecam02 curve. Turning that curve to linear is not an ideal solution, as it doesn’t just remove the artifact, but also changes the look of the image. However in this instance it is not a big deal, as the curve was subtle, and easily replaced with the vibrance module. I suspect this artifact is too rare to worry much about, but the solution is nice to know if it happens again.

Is the bug still present in dev or only 5.8?

It’s still in dev, but things get slightly better. Using CIECAM02 color curve + nearest resize = no artifact. Using CIECAM16 makes those artifacts more pronounce, but no as bad as 5.8.

@Soupy @HIRAM

@jdc changed a few things and added an option in the preferences via this PR
that tackled an issue I had not so long ago (this one).

This PR also seems to fix this problem (I just tried it out).

If you run into white artefacts in your exported file(s), files are completely white after exporting or, when zooming 100+% turns them white when using CIEcam, try unticking this new option:

Preferences → Colour Management → Ciecam → Avoid Artifacts

This issue only turns up in special circumstances so it might not be a good idea to leave it turned off by default (it is actually there to avoid artefacts in general).

EDIT: Words.


Would there be any reason to not change the option to defaul on?


If I understand Jacques’ explanation correctly: It had been on by default, always had been. But up until the issue I filed it was not possible to turn off this build in ciecam artefact safety net.

Now you can turn it off, but it should only be used in those rare situations that everything aligns (in)correctly. If you leave it off you might run into other, more common artefact problems (@jdc: please correct me if I’m wrong…)

Jacues did elaborate a bit more about the inner workings of this very old problem and its solution in the above mentioned/linked PR and issue.


You are true…
I Idon’t think that setting the option “on” is a good choice, because in this case several selections (the ones in question) will be disabled (for example impooible to denoise !). I think it’s better to let the user discover which situation brings the artifacts and not to use .

But you can use also, the experimental branch “lagamcie” which offers an LA version of ciecam that is further upstream in the process (and which I hope will cause less artifact problems). This branch also contains a version of “Jzazbz” and others improvment (gamma Lab ==> linear, etc.)

I wrote a documentation (in french)


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I just integrated lagamcie and gave it a +/- 30 minutes test run: That is a very nice addition to the Local Adjustments tool family! The fact that you can target certain parts (or not, with Scope set to 100) makes this arguably more powerful/useful then RT’s stand-alone CIEcam module.

Any idea when this is going to become mainstream?

Too bad my French sucks :rofl: