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Author Topic: Test image using Apple iPhone 13 Pro (ProRAW mode)  (Read 323 times)

Guillermo Luijk

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Test image using Apple iPhone 13 Pro (ProRAW mode)
« on: September 30, 2021, 05:12:44 pm »

A newcomer to iPhone 13 has shared a DNG file from it:

https://www.dropbox.com/s/k57zpy4p03vx1zz/IMG_3234.DNG?dl=0

These ProRAW files are particular: it has very few filled levels. Even if EXIF data indicate a sat point of 65535 (the limit of the 16-bit scale), the last 2 bits are completely empty:

EV histogram (scene's DR is around 9 stops):
http://guillermoluijk.com/misc/iphone13.gif

Linear histogram: no data beyond level 16384
http://guillermoluijk.com/misc/iphone13lin.gif

Internal baseline exposure is an amazing +4EV. This means when opening the DNG file in ACR, a clandestine exposure correction of +4EV is applied. The file is robust enough to resist this because is the result of a HDR blend, so the shadows retain a high SNR and detail.

http://guillermoluijk.com/misc/iphone13.jpg

I just saw HDR artifacts in the border between the dark tree and the background, both coming from differently exposed shots:

http://guillermoluijk.com/misc/iphone13artefacto.jpg

In this regard the DNG files seem to have the same format, appearance and quality as those from iPhone 12 using ProRAW.

Regards

Manoli

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Re: Test image using Apple iPhone 13 Pro (ProRAW mode)
« Reply #1 on: October 01, 2021, 01:19:17 pm »

The file is robust enough to resist this because is the result of a HDR blend, so the shadows retain a high SNR and detail.

Was the original shot without HDR ?
and, if so, are you saying that Apple is (automatically) applying a +4EV (a clandestine exposure correction ) boost ?
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Guillermo Luijk

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Re: Test image using Apple iPhone 13 Pro (ProRAW mode)
« Reply #2 on: October 01, 2021, 04:59:49 pm »

Was the original shot without HDR ?
and, if so, are you saying that Apple is (automatically) applying a +4EV (a clandestine exposure correction ) boost ?
How exactly the DNG file was built only Apple knows, but for sure it was made from at least 2 shots with different exposure. I guess HDR is activated by default like in most modern smartphones.

Not sure if I understand your question about the +4EV, that is just a metadata value:

D:\iphone\ej1>exiftool -baselineexposure iphone.DNG
Baseline Exposure               : 4.009187698

It informs the RAW developer to apply a previous exposure correction, otherwise the image would render very dark.

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Manoli

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Re: Test image using Apple iPhone 13 Pro (ProRAW mode)
« Reply #3 on: October 01, 2021, 06:52:54 pm »

…  the +4EV, that is just a metadata value:

Thank you, Guillermo., I hadn’t seen that ‘baselineexposure’ metadata tag before (I’m using jfriedl’s exifviewer on an iPhone11 Pro).
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Guillermo Luijk

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Re: Test image using Apple iPhone 13 Pro (ProRAW mode)
« Reply #4 on: October 01, 2021, 07:22:14 pm »

Most cameras have this exposure correction in their EXIF metadata, just to make sure you see a similar exposure to the JPEG when opening them in a RAW developer, but they're usually low values (+0.35EV,...). With these Apple ProRAW DNG files, which are basically HDR composites, I have found values of 2-4EV the usual way.

This is an example of what you see in ACR when opening a ProRAW DNG file wth a +2EV Baseline eposure correction vs when you set it to 0 (I used exiftool for that):



Notice that ACR sliders have the same settings on both cases but the second image renders 2 stops darker.

Regards
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