The third question: purple fringes

[robyferrero]

The purple fringes come to mind.
While DxO tidies everything up, I think so. Can CameraRaw correct them and still get the same linear DNG?

[C.Oldendorf]

We'll find out. I have an image in mind for that I only need to find it which could be hard but if you have one that would be fine as well.

[robyferrero]

The file I just sent you was shot with the worst lens in the world for purple and green fringes.
I haven't checked, but you should find plenty of them in the corners.

[C.Oldendorf]

The file I just sent you was shot with the worst lens in the world for purple and green fringes.

Good just what we'll need

[robyferrero]

As I said, I haven't checked that file.
If it's not particularly obvious, even though I don't believe it, let me know and I'll find something else for you. That lens is absolutely the worst in the world. It's beautiful in every other way, but the purple and green fringing is outrageous. So it's really ideal for this test.

[C.Oldendorf]

We wanted to get to this didn't we, but it got lost.

The attachment Pure-RAW-5-UI.png is no longer available

[C.Oldendorf]

Exploring How DxO PureRAW 5 Deals with Purple Fringing

We wanted to get back to exploring how third-party solutions like DxO PureRAW 5 deal with purple fringing in raw data.

The reason we look at third-party solutions in the first place is that ColorPerfect uses point operations and point operations only. All pixels are processed individually, each governed by the same physical scaffold and rules, but without any interdependency on other pixels. Adjacent pixels play no role in the computational result for any given pixel.

That, in turn, makes the elimination of phenomena such as chromatic aberration impossible, because we simply do not know whether a pixel should be purple by its own right or whether we are seeing an edge effect. To resolve that, we would need a completely different approach to image processing within the plug-in. And again, if that turns out to be an area in which others already excel, why even bother redirecting our resources towards it — especially since this would require a tremendous development effort.

Anyway, I will post a screenshot of the PureRAW 5 user interface as I had it when I made the attached DNGs, using their new model specializing in Fuji X-Trans imaging. These are RAW images that originate from Fuji’s proprietary sensor design rather than from a standard Bayer color filter array.

When it comes to lens and image corrections, PureRAW offers four main options. We can turn the entire lens correction system off. We can turn lens distortion correction on, and once we do, we can select from three possible output types:

1. The image can be cropped to the original aspect ratio.
2. It can be cropped to the maximum rectangle possible.
3. Or we can choose to retain the complete image area.

That last option essentially yields a square image in which the four corners are filled with real image data, while a sort of “cushion effect” appears along the edges — an arched black region where no data exist. This happens because the distortion correction remaps pixels to where they would be if there were no lens distortion, which in turn produces a non-square distribution of the pixels our square sensor originally captured.

This kind of output can be particularly interesting if we are targeting alternative aspect ratios, such as 16:9 or even 2.35:1, thinking in filmic terms.

Now, the fourth setting — turning the entire lens distortion system off — has far bigger implications for all images captured on modern cameras whose lenses are designed around mandatory digital de-distortion.

This may sound odd at first, but it’s an important point. I wrote about it in more detail in an article discussing shortcomings in the current and previous generations of the DNG standard, and I might as well include that text here. It isn’t published on the website yet, but you can all read it here for context, because it will give you a clearer impression of what is actually going on — both with modern lens de-distortion in general and with why the Adobe DNG format is no longer fully fit as an archival medium in this new world.

https://www.colorperfect.com/photo-arch ... t-changes/

That is even in 10 languages already . So, read that first, and then keep the following in mind:
when you turn off the lens de-distortion system in PureRAW 5, it completely removes all originally embedded lens correction data that the camera manufacturer had written into the metadata.

In other words, you will end up with an image that is actually worse off than if you had simply processed the same Fuji RAF RAW file through MakeTIFF using Adobe DNG Converter’s interpolation path — rather than LibRaw’s interpolation path — because PureRAW, in this configuration, discards information that would otherwise have been preserved.

Addendum

I should probably also note that in making the four DNG examples included above, I kept both Vignetting Correction and Chromatic Aberration Correction enabled throughout all three examples that have the Lens Correction System turned on.

I find that the vignetting correction, while it seems to work out quite well, makes direct comparisons to the original MakeTIFF-derived data somewhat difficult. The Chromatic Aberration Correction definitely improves matters — yet it does not completely eliminate purple fringing. You can still see traces of it, for instance, in the lower right corner of the example image.

[robyferrero]

That's a good point, I think.
It does a great job, and you have different levels of adjustment for more or less complicated files.
Too bad it doesn't work on Ventura.

Did the Luminance 40 tool convince you?
You said you had some concerns about the default settings.

But what is the Maximum-Rectangle file?
Has the aspect ratio changed? Is it constructed?

[C.Oldendorf]

Purple Fringes, Redux — 2012 Berlin Mall Revisited

For this part of the series I finally tracked down the picture I had in mind when we first spoke about purple fringes.
It’s a Nikon D300S frame from 2012, taken in a Berlin shopping mall that we visited while my father's sister still lived there. The upper section is filled with rows of lamps — and with them the unmistakable purple halos that once made me think the photo was beyond rescue.

Running it through DxO PureRAW 5 confirms that instinct in an interesting way.
The program’s chromatic-aberration module doesn’t touch these fringes at all — which makes perfect sense.
What we see here is not optical CA in the strict sense but an interpolation artefact produced during demosaicing.
That’s harder to prove conclusively, yet visually it fits: the aberration sits symmetrically around saturated light sources rather than following the lens’s radial geometry.

The resulting PureRAW-derived linear DNG (already demosaiced) behaves beautifully when tested for noise performance — again outperforming the now-discontinued Enhance Details feature that Adobe Camera Raw offered up through version 17.3.

Because PureRAW has already interpolated the mosaic, RAW Details in ACR 17.3 is unavailable, but the built in Denoise AI model still works on a linear file. And that is the small surprise of this experiment: even at a denoise amount of 1, that model quietly removes the purple fringes that PureRAW left untouched.

[Full image link - opens in new tab]

[Full image link - opens in new tab]

So the final workflow becomes:

1. Original Nikon NEF → PureRAW 5 → clean, low-noise linear DNG
2. Linear DNG → ACR 17.3 Enhance: Denoise (1 %) → subtle correction of residual purple fringe

The result is finally what that 2012 image was meant to be: the lamps at the top glow cleanly, no magenta halos even when viewed small, and the rest of the frame keeps its colour integrity.
After more than a decade, the “incorruptible” picture turned out to be quite redeemable after all.

[robyferrero]

All very interesting.
Regarding the residual purple fringes on the lens in question, I think it's among the worst on the market for chromatic aberration.

With other methods, I've done much worse; you remove them from one side, and add them to the other; they're really heavy fringes.

When it comes to removing them on the Leica, everything is much easier.
In fact, I can eliminate them much better on the toy Holga lens with its plastic lens, than on the Fujifilm 18mm XF f:2 R—imagine that!

I can show you even worse; in this file, they're almost exclusively in the corners. When the fringes are present further in the center, it's a bigger problem.

I won't say anything about distortion—we've already seen that, but there's worse; if you want to be scared for a moment, just open a file from the Fujifilm 35mm XF f:2 R WR.

These lenses are beautiful for other reasons, but as for flaws, if it's not one, it's the other.

In PureRAW, I can even keep the vignetting.

[robyferrero]

Basically, depending on the photo, you may need to use both.

What's no longer in CR; right click -> enhance -> details -> noise -> DNG, it's still available in the Details module, the problem is that you no longer get a DNG.

[C.Oldendorf]

Basically, depending on the photo, you may need to use both.

Yes, that was an interesting finding. I did not expect that it would make sense to ever use both. But for this specific adjustment of pink halos around bright light sources, it was actually quite beneficial.

What's no longer in CR; right click -> enhance -> details -> noise -> DNG, it's still available in the Details module, the problem is that you no longer get a DNG.

Yes, in our workflow the key step used to be: open the native raw in ACR or Lightroom, invoke the Enhance command (for Denoise, Raw Details or Super Resolution) and obtain a separate ‘Enhanced’ DNG file — a demosaiced, processed-but-raw intermediate that could then be handed off to ColourPerfect/PerfectRaw. With the April 2025/June 2025 releases (ACR 17.4 / LrC 14.4) Adobe changed the pipeline: the enhancement is now done in-place (non-destructive) inside the Develop/Detail panel and does not produce a standalone DNG that you can export for downstream raw-level processing. In short, the export-DNG path is removed. For users who require that exact intermediate the only reliable option is to retain ACR 17.3 or earlier, and LrC 14.3 or earlier.

Download links (archive these while you can):
macOS: https://download.adobe.com/pub/adobe/ph ... w_17_3.dmg
Windows: https://download.adobe.com/pub/adobe/ph ... 17_3_1.exe

[C.Oldendorf]

Did the Luminance 40 tool convince you?
You said you had some concerns about the default settings.

I initially thought the Luminance slider might have something to do with image brightness — something like fill light or a general tonal shift — because I did observe brightness differences in my first tests. That, however, turned out to be caused by vignetting removal from the optical corrections, not by the slider itself.

The Luminance control in DxO’s terminology is just very unintuitively worded if you ask me. It doesn’t affect image brightness at all — it governs how strongly the denoiser acts on luminance noise, that is, the brightness-channel grain component of the image. In essence, it determines the amount of smoothing applied to the noise structure rather than to the tone curve.

While some users prefer to keep a certain amount of luminance noise to preserve texture, I’m generally fine with the default setting. I tend to add film-derived granularity later anyway, so for my workflow the output can be as clean as possible at this stage — even if it looks somewhat “too perfect” on its own. The artificiality is only temporary, since I re-introduce a natural grain pattern later in the process.

So in short: Luminance 40 is not about brightness, it’s about luminance-noise reduction strength. The name just happens to be misleading.

But what is the Maximum-Rectangle file?
Has the aspect ratio changed? Is it constructed?

In the maximum rectangle file, the aspect ratio has indeed changed, but the image is not artificially constructed. The full image area file, by contrast, represents the entire geometric de-distortion output — essentially everything the lens and sensor system have recorded after pixel remapping. This is the true, untrimmed result of the distortion correction process, typically showing the arched black borders that indicate areas where no sensor data exist.

Modern cameras usually crop this geometrically corrected image back down to match the native sensor rectangle when producing in-camera JPEGs, and most RAW processors follow the same convention. That cropped version is what we see as the “regular image.”
The maximum rectangle file, meanwhile, keeps the same vertical extent as the regular image but extends the horizontal frame as far to the left and right as real data exist within the corrected geometry. The maximum rectangle image is not in any way synthetically generated. It contains only what the lens actually projected onto the sensor, passed through the geometric de-distortion process — which, in many mirrorless lens designs, is not a mere correction step but an integral part of how the optics were designed to begin with.

[robyferrero]

What's no longer in CR; right click -> enhance -> details -> noise -> DNG, it's still available in the Details module, the problem is that you no longer get a DNG.

Yes, in our workflow the key step used to be: open the native raw in ACR or Lightroom, invoke the Enhance command (for Denoise, Raw Details or Super Resolution) and obtain a separate ‘Enhanced’ DNG file — a demosaiced, processed-but-raw intermediate that could then be handed off to ColourPerfect/PerfectRaw. With the April 2025/June 2025 releases (ACR 17.4 / LrC 14.4) Adobe changed the pipeline: the enhancement is now done in-place (non-destructive) inside the Develop/Detail panel and does not produce a standalone DNG that you can export for downstream raw-level processing. In short, the export-DNG path is removed. For users who require that exact intermediate the only reliable option is to retain ACR 17.3 or earlier, and LrC 14.3 or earlier.

Download links (archive these while you can):
macOS: https://download.adobe.com/pub/adobe/ph ... w_17_3.dmg
Windows: https://download.adobe.com/pub/adobe/ph ... 17_3_1.exe

Very good, thank you.
If we wanted to install ACR 17.3 on a later version of PS, where ACR is already installed, how can we do it? Do we need to uninstall the previous version first, can we simply overwrite it, or can we keep both?

[C.Oldendorf]

If we wanted to install ACR 17.3 on a later version of PS, where ACR is already installed, how can we do it? Do we need to uninstall the previous version first, can we simply overwrite it, or can we keep both?

The installer overwrites globally for all versions of PS CC. That was 2023+ on the macOS 26 box I tested this on.
As for parallel installation. I'm suppose it can be done but I need to look at what files to copy out and put where

[robyferrero]

If we wanted to install ACR 17.3 on a later version of PS, where ACR is already installed, how can we do it? Do we need to uninstall the previous version first, can we simply overwrite it, or can we keep both?

The installer overwrites globally for all versions of PS CC. That was 2023+ on the macOS 26 box I tested this on.
As for parallel installation. I'm suppose it can be done but I need to look at what files to copy out and put where

Leave it alone now, with all the things you have to do.

We'll reconsider if necessary.

[C.Oldendorf]

This observation I should document:

If we try to use Enhance Denoise directly on the NEF, ACR fails miserably.
That is on the actual color filter array raw image of the Nikon D300S.

Enhance_on_NEF.png (199.33 KiB) Viewed 454 times

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If we use the same settings on a DNG that has already been interpolated things work like we saw with the output from PureRAW 5 the other day:

Enhance_on_interpolated_DNG.png (200.36 KiB) Viewed 454 times

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In order to make such a DNG file that is already interpolated we need to tell DNG Converter, or if we routinely want such I can make MakeTiff be able to put them out easily. Here is the way to do it manually:

dng_converter.png (252.73 KiB) Viewed 454 times

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[robyferrero]

I'm doing it manually.

In Custom Compatibility, I see that the "Uncompressed" checkbox needs to be unchecked.

And in Preview/Fast Loading Data; no JPEG preview and uncheck "Embed Fast Loading Data."

[C.Oldendorf]

In Custom Compatibility, I see that the "Uncompressed" checkbox needs to be unchecked.
And in Preview/Fast Loading Data; no JPEG preview and uncheck "Embed Fast Loading Data."

The first is not relevant. Uncompressed just makes a bigger file. It is a lossless compression.
The second is also not relevant. Again embedding a JPEG bloats the file, I don't need one for this.