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Author Topic: Leica M11's sensor is a conventional Bayer sensor  (Read 1021 times)

Guillermo Luijk

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Leica M11's sensor is a conventional Bayer sensor
« on: January 16, 2022, 11:32:31 am »

Leica claims the new Leica M11 can produce 3 different output resolutions, both in JPEG and RAW. This could lead to think that the camera uses some CFA that allows for pixel binning techniques to produce different resolutions. But the sensor happens to be a standard 60Mpx RG/GB Bayer sensor (which BTW is the most logical way in order to prioritize image quality at the highest resolution), so the 36Mpx and 18Mpx shooting modes should just be downscaled versions of the 60Mpx demosaiced RAW data.

I am a bit surprised at why Leica is putting so much effort in marketing these lower resolution modes, claiming an improvement in SNR and DR, which is a common consequence of any pixel downsizing procedure.

There are RAW files available at DPreview:

http://guillermoluijk.com/misc/leicam11.jpg

200% crop of processed RAW file and RG/GB Bayer pattern:
http://guillermoluijk.com/misc/leicam11crop.jpg

D:\leicam11>dcraw -v -i *.dng
Filename: L1000504.DNG
Raw colors: 3
Filter pattern: RG/GB
Timestamp: Sun Dec 12 18:45:05 2021
Camera: Leica M11
DNG Version: 1.4.0.0
ISO speed: 64
Shutter: 1/128.0 sec
Aperture: f/4.8
Focal length: 0.0 mm
Number of raw images: 1
Thumb size:  9504 x 6320
Full size:   9536 x 6336
Image size:  9536 x 6336
Output size: 6336 x 9536
Daylight multipliers: 3.820809 0.967847 1.426022
Camera multipliers: 3.851563 1.000000 1.527344 0.000000

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Guillermo Luijk

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #1 on: January 16, 2022, 11:59:09 am »

Surprisingly, in Amateur Photographer have analysed that the 36Mpx and 18Mpx output modes keep the RG/GB Bayer pattern, which means some form of new downscaling implemented by Leica:

https://www.amateurphotographer.co.uk/reviews/compactsystemcameras/leica-m11-review

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Manoli

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #2 on: January 16, 2022, 12:28:34 pm »

... which means some form of new downscaling implemented by Leica:

https://www.amateurphotographer.co.uk/reviews/compactsystemcameras/leica-m11-review

Quote
This isn’t the first time we’ve seen ‘small RAW’ files […] But it seems like Leica is doing something technically very different. Where these other sRAW formats involve demosaicing the raw sensor data and downsampling the resultant full-colour file, examining the M11’s DNGs using RawDigger reveals that Leica is simply outputting lower-resolution, un-demosaiced files.

This looks like such an obvious approach that you’d be forgiven for wondering why other cameras don’t all do it already. The likely reason is that, theoretically, interpolating and downsampling the individual colour channels like this could be open to producing imaging artefacts with finely-repeating, low-contrast detail. However, there’s no obvious problems with our landscape comparison above.
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Guillermo Luijk

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #3 on: January 16, 2022, 01:22:06 pm »

Not that simple:

DNG™
L-DNG 60,3 MP 9528 x 6328 pixels
M-DNG 36,5 MP 7416 x 4928 pixels
S-DNG 18,4 MP 5272 x 3498 pixels

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mcbroomf

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #4 on: January 16, 2022, 02:39:09 pm »

So it boils down to whether Leica's downsize interpolation of the colour channels before demosaic (if AP is right) is equal to, better, or worse than a straight interpolation after the full image is demosaiced.  I'm not sure these days unless you are a dedicated sports/wildlife/journalist (for eg) type shooter who shoots thousands in one session that you need smaller files, and in that case most (from what I understand) want jpg so that they can fly from camera to editor without being touched by the photographer.
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Guillermo Luijk

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #5 on: January 16, 2022, 05:03:25 pm »

So it boils down to whether Leica's downsize interpolation of the colour channels before demosaic (if AP is right) is equal to, better, or worse than a straight interpolation after the full image is demosaiced.
The downsize interpolation process is lossy, so I think it's safe to say you'll never get anything with the 36Mpx or 18Mpx modes that cannot be achieved or improved in terms of image quality using the original 60Mpx RAW data. The usefulness of these lower resolution modes comes when the advantage of smaller files is greater than the quality loss.

However what we know so far is that the camera produces undemosaiced DNG files (or we'd better say to-be-demosaiced DNG files), but it remains a mystery whether the original RAW data is demosaiced at some point in the process or not. I can think of two possibilities:
  • Each individual RAW channel: R, G1, G2, B (maybe with some interaction/combination of the highly correlated G1 and G2) is individually downsampled to the final size. This is totally possible, but would require a fine tuned previous AA filtering. We must think that the sampling frequency of partial RAW channels: R, G1, G2, B is half the sampling frequency of the sensor.
  • The original RAW data is demosaiced, then properly rescaled to the final size (the required AA filtering here would be less critical since we already have standard RGB data, so we take advantage of a higher sampling frequency over the whole image), and finally 2 out of each 3 channels on every pixel are dropped to form a new fake-Bayer smaller DNG file. Not sure if this last step makes sense vs the need to demosaic the data again.

I can see advantages and disadvantage on both approaches, but the first being more complex makes more sense to me and I find it more attractive from an engineering/signal processing perspective.

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« Last Edit: January 17, 2022, 09:08:12 pm by Guillermo Luijk »
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SrMi

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Re: Leica M11's sensor is a conventional Bayer sensor
« Reply #6 on: February 27, 2022, 05:27:03 pm »

The quality of lower resolution files (M-DNG, S-DNG) is similar to the resized full resolution (L-DNG) file quality. I do not know of any other manufacturer that can provide smaller resolution raw files without a quality loss.
It is not clear how they do that, but the chosen resolutions are limited by the algorithms used. E.g., 24MP mode was not possible.
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