[Leica] Yet another surprising fact about the M (240)

[Herbert Kanner]

I was surprised to see in the manual that there was lossless compression of the DNG. So I thought I’d try it out by taking two shots, one compressed and one uncompressed. When I looked at my DNG file, I was astounded to find a DNG of over 40 MB and a compressed one of about half that size. (I deleted the negatives before thinking of writing this, so I can’t give you exact numbers.

Well, I was at first astounded that lossless compression could be that effective. Then I thought about the details of an image. Except where there is really fine structure in the image, there will be areas where the data does not change. A simple number triple, one giving a value for, say the red pixel, the second giving a starting location in the file, and the the third the number of consecutively stored pixels having the same value, could easily result in a factor of two compression for lots of pictures. And what I just described is a very unsophisticated compression method. If anyone knows more about how this might have been done, I’d be very interested.

kanner at acm.org
650-326-8204

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