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Using CHDK with my Canon A550 I get DNG files that do not have an embedded preview image only a very small thumbnail (see this question). However, alongside the DNG a full resolution JPEG file is created by default. Can I somehow use that existing JPEG file as the DNG preview? Is there some kind of tool to take that file and embed it inside the DNG? If so, would that be faster than generating and embedding DNG previews via Lightroom?

The JPEG and DNG files have the same filename except for the extension.

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I think you should be able to do it using "exiftool" --- I tested on a Linux PC, via commandline, and with a Sony ARW image, so your mileage may vary --- I have no DNG to test with.

The command is basically: 

exiftool '-previewImage<=myown.jpg' test.arw

(the quotes are needed in Unix to prevent the shell interpretation of <=). I have a bit of problems with the orientation of the embedded preview, but probably you can work out a solution with a bit of testing.

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  • The command runs but doesn't change the DNG file in any way. It outputs: 0 image files updated; 1 image files unchanged
    – Saaru Lindestøkke
    Jan 22 '14 at 16:57
  • Maybe that does not work with DNG. Worth asking to the exiftool developers, I think.
    – Rmano
    Jan 22 '14 at 17:11
  • It worked for me on this DNG file I have version 9.13 on Linux Ubuntu.
    – Rmano
    Jan 22 '14 at 17:45
  • I've posted on the exiftool forum to see what's going on. This is the JPG file I'm trying embed in this DNG file
    – Saaru Lindestøkke
    Jan 22 '14 at 17:53
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    I've got a response there saying that, because my original DNG image lacks a previewimage field in the exif info, Exiftool can't be used. The previewimage field needs to be present before Exiftool can add a JPG to it. Exiftool is unable to create the previewimage field by itself because it can't modify the directory structure of a TIFF-format image. Thanks for your help though.
    – Saaru Lindestøkke
    Jan 22 '14 at 18:11

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