Purple on highligths

Hello all,

I request your opinion on the following redering difference between ART (1.4) and RT (5.8).

Situation :
A short (and nice visit) to l’Abbaye de Saint-Benoit (FRA/25). Light was very bright so I had to backet my photos (-2/0/+2 IL) and used a tripod.
Fair enough, I do this for years with RT + Photomatix (2.0) or Luminance HDR (2.6)

Problem :
This time I used ART. No difference on the 3x jpeg producted, but once loaded into LuminanceHDR, highlights are displayed purple.

  • I did the same with RT and did not get the purple
  • I tried to use Photomatix and got the same issue
  • I tried another photo serie and get the same constant issue with ART and not with RT

See captures (all default settings in ART, RT and Photomatix)

Any idea ? Thank you

The magenta cast happens when white balance correction is applied to saturated pixels. The three channels pile up at the saturation point, and when the white balance multipliers are applied, those piles separate and what was once white changes to another color, usually magenta.

Since the rest of the image in both captures seems to be similarly exposed, I’m going to surmise that some sort of highlight reconstruction is turned on in the ‘not-magenta’ image processing…

Can you share the raws? Thanks!

Maybe your RT default profile has highlight reconstruction turned on, while it is turned off in ART?

Have you fittled with the white point?

Hi Sebastien,
Thank you for your support.
Highlight reconstruction is turned on by default in RT
Highlight reconstruction is on blend in ART by default

Hi Mica, thank you for your support
Basically, I open RT/ART, put the 3x Raw into the waiting queue and initiate the post prod, no change, no correction (-> as a consequence having a look to the screenshoots, you may notice my AWB 5D faced a “kind of” problem at the time of the shooting :smiley: ).
Default settings difference is a good investigating direction indeed

Hello ggbutcher,
Thank you for the idea, that you imply I have to investigate into the defaut settings/prefs…

This photo is sold so I cannot share the RAW but I upload another triplet that face the same challenge
200722_16h59-9214.CR2 (23.5 MB) 200722_16h59-9215.CR2 (25.2 MB) 200722_16h59-9216.CR2 (27.6 MB)

What I did in ART: opening the directory containing the photos in the file browser, directly putting the photos in the queue, process queue . Then Highlight recovery is OFF and you get the purple zones.

What you should do : create a profile dedicated to this work

  • open one image and apply neutral (if you want avoid any processing)
  • enable Highlight recovery/blend or color propagation.
  • to recover completely the highlights you should set tone equalizer/white=-40
  • select camera input profile “color management/auto-matched camera profile” unless your colors risk to be borked
  • demosaicing rcd+vng4
  • chromatic aberration correction/automatic
  • close photo ( it creates a profile alongside the photo)
  • in browser copy paste the profile on all photos and send to queue
  • you can also save the profile in <yourconfigfolder/profiles> and use it in the queue: apply the following profile on export
  • you can also set this profile as your default profile

Hello gaaned92,
Thank you for the time you have spent on the serie to achieve the best way to get rid of the purple color. I certainly will compare your procedure to mine then I can improve.
That being said, the question I have is to better understand why ART is generating purple with default settings and not RT.

I reproduce the process with Highlight reconstruction disabled (and tonal curve set to linear to increase the effect). See capture. I joigned the image params as well.

200722_16h59-9216.CR2.arp (10.2 KB) 200722_16h59-9216.CR2.pp3 (11.2 KB)

Wouldn’t it be in relationship to the fact that RT relies on dcraw while ART uses libraw?


This is expected – see the explanation by @ggbutcher. If the highlights are clipped, you commonly get magenta highlights. To correct them, use highlight reconstruction.
And btw art doesn’t use libraw yet – it might in the future but right now it shares the decoding part with RT

Using ART, simply setting Highlight reconstruction to “Blend” removes the magenta in highligths.
Left: no reconstruction - Right: with highlight reconstruction in Blend mode

Hello all,
It looks like we’re not fully aligned on the topic but as the comparison of the result achieved between RT and ART in default mode doesn’t seems to be relevant to anyone, it leads me to the conclusion that this is not important.
Thank you anyway!

The type and the order of some processes in the pipeline are definitely different between RT and ART, so yes you can expect differences when you compare both.
But if you think we missed your point, you can write in French… Peut-être que nous nous comprendrons mieux ainsi :wink:

Edit: rewrite of post

When sending a photo with NO profile to the queue:

  • RT applies the default profile as it is defined in the preferences.

  • ART also applies the default profile as it is defined in the preferences. select as default profile “auto-matched curve” or a profile built by you.

But it seems that, in both cases RT and ART, if you defined as default profile a dynamic profile, it is not selected in the queue and the neutral profile is used.

In RT you don’t get the purple zones as “clip OOG” is selected in neutral profile,

If you want to apply dynamic profile in ART you will have in browser to select images and apply “processing profile operations/reset to default”.

Can somebody verify above observations?

Actually, what that difference and this discussion did for me was to finally clarify my understanding of what highlight reconstruction does regarding the so-called ‘clipped channels’. I incorporated RT highlight reconstruction in my hack software, and even with patient explanation by @CarVac I didn’t quite get it until now… So, en francais, vive la différence!

(Disclaimer: my French is South Louisiana Cajun, extremely limited, and I had to do this sentence with the assistance of Google Translate… :face_with_raised_eyebrow: )

@fedelin could you upload your RT and ART default profiles as defined in preferences/image processing/default profile?