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Canon DPP4 gives extra pixels on raw conversion?

 
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19978
Location: Richland, Washington State, USA

PostPosted: Mon Jun 10, 2019 2:14 pm    Post subject: Canon DPP4 gives extra pixels on raw conversion? Reply with quote

A user of Zerene Stacker has reported to me that raw converting with Canon DPP4, from his 7D Mk II camera, gives different size images from one frame to another.

In four frames shot as a focus stack, he saw
Code:
Image 1:  57.1 M      5475, 3649
Image 2:  57.2 M      5475, 3650
Image 3:  57.2 M      5475, 3650
Image 4:  57.1 M.     5474, 3649

The nominal specification for 7D Mk II is 5472 x 3648, so it seems that DPP4 is giving a couple of extra pixels, but not always the same number.

I find this quite strange, so I am curious.

Does anyone know why this happens? Especially, why is it different from one frame to another?

--Rik
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Pau
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Joined: 20 Jan 2010
Posts: 4805
Location: Valencia, Spain

PostPosted: Mon Jun 10, 2019 3:03 pm    Post subject: Reply with quote

Just a possibility, but could it be due to a compressed raw format?
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Pau
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Mon Jun 10, 2019 3:21 pm    Post subject: Reply with quote

Quote:
could it be due to a compressed raw format?

Does not seem likely. Compression on raw files is normally completely lossless. I've heard of a few raw formats that do lossy compression in some circumstances, but if I recall correctly that was described as slightly altering pixel values, not image sizes.

Lightroom converts all four of these raw files to the same size output, 5472 x 3648.

--Rik
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apt403



Joined: 06 May 2019
Posts: 37
Location: Yelm, WA

PostPosted: Tue Jun 11, 2019 12:08 pm    Post subject: Reply with quote

Total shot in the dark without having access to the files, but perhaps it's some weirdness going on with the way DPP4 handles RAW demosaicing, specifically where it chooses to crop the edges.

I'm seeing 5472 × 3648 quoted as the max effective resolution for the 7D Mk II from various sources, smaller than the sizes reported by the user. Perhaps DPP4 is leaving some 'extra' pixels in the image that would normally only be used for interpolation. It'd be interesting to run the raw files through a different raw processor, and maybe view the raw bayer output before demosaicing.
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