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In doing some testing with the DNG Converter, I'm seeing file size differences in the resulting DNGs tied to the preview image size that I can't understand.
If I convert the same RAW file with a Large preview image and with No preview image I am consistently seeing size differences of 6-7 megabytes between the resulting files (i.e. the DNG with the Large preview images is 5-7 megabytes larger). This is outputting Camera Raw 14 compatible images, if I switch to 15.3 compatibility the size difference goes down to 2-3 megs. The file size delta is fairly consistent if I go between Lossey compressed DNGs and Uncompressed - the one with the Preview is always a few megs bigger.
If I use exiftool to extract the preview image (using exiftool -b -PreviewImage -w .jpg), the jpg file is only around 50 kb for the DNGs that have the Large preview image embedded.
Why is the DNG file with the embedded preview image so much larger when the preview JPG is only 50KB?
Here are some actual data:
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