For what it's worth, I've been comparing the DNG files created by CHDK on both of my Canon cameras (the powershot sx1 and the powershot a720) to see if I can figure out why Adobe Camera Raw rejects one, while accepting the other:
http://www.ibbu.nl/~nsprakel/winhex1.jpgWith photoshop, you can select the data on the right and superimpose it on the data on the left in difference mode, to find
the differences between both files. I've blurred those differences and superimposed it in a blue color on the left side, to
highlight the differences:
http://www.ibbu.nl/~nsprakel/winhex2.jpgIn winhex1.jpg, you can see a small marked section of 8 bytes from offset 457 to 45E (hexadecimal) in the header of both DNG files. It turns out that if you modify the DNG to ensure the first and last byte match, the DNG will be recognized by ACR, but the thumbnail is not displayed properly in the windows explorer.
In this specific case, that means I have to change the first and last byte (of the marked sequence of 8 bytes) in the file CRW_0880.DNG:
0E -> 0C (at offset 457)
18 -> 08 (at offset 45E)
When those two bytes are modified, the DNG file can be loaded in ACR. So apparently, it's a simple issue with the header of the DNG file.
Maybe someone else can figure out how to get the thumbnail to display properly. :-)
