Q2M - Bracketing Merge file size reduced

[MartinP]

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A typical Q2M DNG file size is around 88MP, when I use the bracketing option and take three images, then In Lightroom 'merge to HDR' the resulting DNG file size is smaller than one original DNG, i.e.  one original file size 88MP, after merging three 88MP dng files the resultant dng file is 69MP!  Just wondering why it is so small, I would have expected it to be lot larger than 88MP... Any ideas/suggestions, thanks 

[jaapv]

A file size is not measured in MP, that is for sensor size. There is no reason for a HDR file to be larger, it just assigns other values to the same number of pixels and does not add files up. Lossless compression or noise reduction can easily account for a reduction in file size in Bytes, 

[marchyman]

In addition to jaapv's comment the DNG files out of the Q2 and original Q are not compressed.  I suspect the same is true of the Q2M.  Files created/updated by Lightroom are compressed using a no-loss algorithm.  The only thing you lose with compressed files as a very small bit of time whenever Lr needs to access the original image.  On a modern computer you'll likely not notice it.

The image files from my original Q are typically in the 40-44 MB (byte, not pixel) range.  If after importing I use the Metadata -> Update DNG Preview and Metadata option in LrC the DNG file will be compressed with a resulting file size in the 25-30 MB range.

[vir2l2k]

a hdr is 32 bit so technically it is bigger than the 14 bit but efficient compression seems to be the key

[SrMi]

9 hours ago, vir2l2k said:

a hdr is 32 bit so technically it is bigger than the 14 bit but efficient compression seems to be the key

I believe that 32 bit is an option in PS while LrC uses 16 bit HDR merge. 

[vir2l2k]

apart from compression, the original dng is in fact 50 mpx (as the resulting 46 mpx image is in fact a crop from the 24mm lens that is software corrected, looking close to an 28mm) whereas I believe the merge into hdr will result in a 46mpx image, this might be minor, but may also play a role. biggest part may be the compression though. I'm also a bit unhappy with the very large file sizes but I'll guess my next mac will just come with 4 or 8 tb internal ssd then.