AP's 32bit HDR .png files turning into SDR when edited inside Apple Photos?

[F_Kal]

I've been trying to create HDR-merges in AP2.x that are able to render as real-HDR on the OLED display of my iPhone, but it has been hit-or-miss. 

Process I merge -2/0/+2eV RAW images inside AP2.x (the RAW developer persona delivers 32bit HDR). I do not use the tone-mapping persona. I edit them to my liking and export the result into 32bit/BT.2020 PQ/full Range PNG. Then, I import this image into my phone's Photos library (eg via airdrop)

Behavior

Inside Apple Photos, the thumbnails appear as SDR which is expected. When opening an individual image it lights-up into it HDR potential (also expected). The problem however is that for some of these images (I'd say ~1 out of 2) after I click the edit button, the image gets tone-mapped into SDR and the image loses its extended dynamic range.

In the attached samples, the xxxx271.png and xxxx520.phg files, exhibit the issue in their highlights (look on the light sources and the sky behind the branches) whereas the 3rd image xxx661.png works fine.

Has anybody found what is triggering this inconsistent behavior and perhaps how one could circumvent it until better support comes out?

Notes

I haven't found any connection between the issue and the specific exposure level or curves I use during the AP2 editing, however I try to keep the Max values in the histogram below 1.5. - The image will have the issue whether the filter/editing layers are active or not. I wonder if the issue has to do with the percentage of pixels with brightness above a certain level (in other words the distribution of the histogram). Another interesting glitch for some HDR photos that I create via this method, is that when transitioning from thumbnail to full-sized image in Apple Photos, the "illumination/brigthening" of the EDR pixels doesn't happen smoothly like it does for the iPhone's photos, but for some images it happens abruptly in 1 or 2 steps. These issues get inherited to HDR jxl files that I convert from AP2s PNG using cjxl. I understand that HDR support on iOS devices beyond HEIC+gain map is still very fresh and not well-standarized of course.

 

 

 

samples.zip

[Ldina]

@F_Kal I don't do a lot of HDR, so take my comments reservedly.

I opened your three HDR images in AP v2.5.5. All 3 open fine, but as SDR images. If I open the 32-bit Preview Panel and click on Enable EDR, all the images display that extended dynamic range on my MacBook Pro (Ventura). 

I then added them to Apple Photos. The thumbnail, as you mentioned, it dull and flat. If I right-click on the image in Apple Photos, and choose Edit in Affinity Photo 2, it opens fine, but again, the 32-bit Preview shows EDR UNchecked. If I check EDR, the extended brightness levels reappear on all three images. 

My MBP has a Retina display that has a 2.00EV Max (+1.00 EV). But, you said you limited your images to 1.5EV so I should see all the tones in your image, I guess. Some tones do exceed 2.0EV, which I can see if I click Clip to Maximum while EDR is enabled. 

Hopefully, this simple checkbox is all you need?

[F_Kal]

thanks @Ldina -

From what I understand the "show EDR" checkbox is merely a previewing setting for Affinity Photo - It's not affected by (neither affecting) some inherent property of the file - it's just a switch to allow the user preview an EDR and an SDR version of his work while working. Hence, this behavior was also expected.

My experience also suggests that Affinity Photo displays properly the images. The problem lies when editing these images inside Apple Photos on an iphone or mac (ie not by exporting them to AP2, but by using the built-in, non-destructive Edit function of Apple Photos)

 

[Ldina]

2 minutes ago, F_Kal said:

The problem lies when editing these images inside Apple Photos on an iphone or mac

Ahhh....sorry, I misunderstood. Yes, all seems fine in AP. I rarely use Apple's built-in editor on any Apple device, so I doubt I can be of much help. 

[F_Kal]

4 hours ago, Ldina said:

My MBP has a Retina display that has a 2.00EV Max (+1.00 EV). But, you said you limited your images to 1.5EV so I should see all the tones in your image, I guess. Some tones do exceed 2.0EV, which I can see if I click Clip to Maximum while EDR is enabled. 

regrding this comment, you raise an interesting point what I haven't been able to find a clear answer to so it would be nice if serif came up with some clarifications.

My personal explanation of all that is that histogram's Max:2 doesn't mean 2.0eV.

Max: 1 is the total range of SDR images which should be around 6 to 12eV (I'm uncertain on the exact value) and 200% would imply double that (12 to 24eV). max:1.5 would give you 12 to 16 stops. Merging 3 HDR images of -2/0/+2eV shot on a mirrorless camera with say 11eV dynamic range, means that you end up with a total of 15eV - Hence the choice of 1.5 but again, this was arbitary on my part. 

As for the retina display showing max 2.0 (+1eV) I think it means that the "previewing" algorithm of AP will try to display all tones up to 2 of the histogram (ie the first 12 to 16eV of the HDR range with probably some tonal compression of the values so they fit in the retina's limited dynamic range) and reserve 1 extra eV as headroom to map all the stronger values as superbright pixels. Once again I might be totally wrong.

An official explanation would be great!

[F_Kal]

20 hours ago, F_Kal said:

An official explanation would be great!

Perhaps @James Ritson?