On Thu, 20 Sep 2007 06:22:14 -0600, Alex Feldman <[EMAIL PROTECTED]> wrote: > This is getting off the topic of the Gimp, but you've piqued my > interest. I just took a digital photo and modified it very slightly > with the Gimp, and used exiftool to print out the exif data for the > original and the modification, and diff'd the two exif outputs. The > only things I saw that might have made a difference were fields called > "Y Cb Cr Sub Sampling" and "JFIF Version". I don't know what these are, > but neither one screamed Gimp!, at least to me. Is there an exif field > I am missing? Is there another tool for looking at all this data?
Using exiftool will only give you a part of the EXIF information, and EXIF is only a part of the metadata available in the JPEG file. You will get a lot more information about the layout of the various blocks contained in the file by using exifprobe instead of exiftool. Although exifprobe shows much more than the EXIF metadata, it does not show you an additional bit of info that can be useful when trying to identify forgeries: what software has created the JPEG quantization tables used in that file. In case you are not familiar with JPEG compression, these tables define how the luminance and chrominance components of the image are compressed. Most cameras use their own tables, Adobe uses their own tables in Photoshop and other products, GIMP uses the IJG tables, etc. That's why I suggested using the jpegqual test tool that I included in the GIMP source tree (only in SVN for the moment). That program allows you to check the quantization tables used in a JPEG file and guess what program or device could have created them. This program is very incomplete and not intended for general distribution (I wrote it to validate some algorithms used in the jpeg save plug-in), but you can already have some fun with it. -Raphaël _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
