So, with a bit of newfound time to spare, I dug into the metadata thing. One thing about the metadata tools, exiftool and exiv2, they won’t display the subifd tags for the various images included in a raw file. However, in exiv2’s samples, exifprint will happily display it all. So, I pulled that out of the exiv2 source tree, compiled it separately, and used it to display all the metadata of one of my NEFs. The relevant file offset and data size are found by running exifprint with a grep for ‘Strip’, like this:
$ exifprint DSG_3111.NEF |grep Strip
Exif.Image.StripOffsets 0x0111 Long 1 114732
Exif.Image.RowsPerStrip 0x0116 Long 1 120
Exif.Image.StripByteCounts 0x0117 Long 1 57600
Exif.SubImage2.StripOffsets 0x0111 Long 1 1645472
Exif.SubImage2.RowsPerStrip 0x0116 Long 1 3280
Exif.SubImage2.StripByteCounts 0x0117 Long 1 17885222
SubImage2 is the raw data we’re looking for; Image is a thumbnail. The relevant tags are: 1) RowsPerStrip, which in this case 3280 is the number of rows in the image data, so the full data set is in one strip; 2) StripOffsets, which is the distance into the file to find the data, and 3) StripByteCounts, which is the data glob’s size. I modified reallyraw2dat.cpp’s printf to print the rawimage and imagesize variables and the values are the same as StripOffsets and StripByteCounts for the same NEF.
Applying the same thinking to a Panasonic RW2, I used exifprint to extract the same information:
$ exifprint P1013104.RW2 |grep Strip
Exif.PanasonicRaw.StripOffsets 0x0111 Long 1 4294967295
Exif.PanasonicRaw.RowsPerStrip 0x0116 Long 1 3664
Exif.PanasonicRaw.StripByteCounts 0x0117 Long 1 0
Well, the same approach isn’t going to work here, the StripOffsets number is larger than the file size and the StripByteCounts doesn’t support the thesis.
Back to the drawing board… the xxx_load_raw() routines will probably give up secrets, but I’m afraid there may be no homogeneity in the approaches…