A DNG file is a TIFF file with a specific structure that includes a low-resolution preview and special metadata. The overall file content, however, is different. (I won't muddy this answer with a technical explanation - add a comment if that would be of interest here.) This can be done using Linux dcraw and imagemagick command-line tools: $ diff -s \įiles /dev/fd/63 and /dev/fd/62 are identical This can be proved by extracting and comparing that data. The image pixel data contained in raw TIFF and DNG files produced by VueScan is identical. The larger image is the save-tiff image with the scanner's calibrated ICC profile instead of the default sRGB. The save TIFF file is the only one with an embedded ICC profile and that is "sRGB IEC61966-2.1".īelow (on the left, the smaller image) is a snap of the VueScan preview, which I would say looks closest to the save TIFF file. There is very little difference between the raw and save DNG files but the TIFFS are quite different, and the raw TIFF is significantly different to the others. Here are Lightroom histograms for four images:Īll four histograms are different, which would indicate that is more than a simple format difference between TIFF and DNG. (I have sought answers in the manual and bible prior to asking here.) Additional information How do these formats differ, especially considering an archival use-case and, with VueScan being the tool of choice, do these differences make VueScan's DNG or TIFF more appropriate for archiving? Without understanding this it's difficult to select the most approproate file to archive. So I can see the formats have different outputs but I don't understand all of the differences, some of which are unexpected - such as the file sizes and the reported gamma values. But why is there such a huge size difference between the LZW compressed TIFF files when the uncompressed TIFF and DNG files are the same size ?Ĭonsidering the above, I would choose between the LZW compressed TIFF (because it is the smallest) or uncompressed raw TIFF unless there is a compelling reason to use DNG. The DNG files being the same size as the uncompressed TIFF suggest to me that the ZIP compression is ineffective. ZIP OR LZW), only whether it is on or off, and that is only for TIFF the DNG format is always ZIP compressed. There is no option in VueScan to select the compression mechanism (i.e. The differences that I identified were in what Imagemagick reported as the Channel statistics plus, in the DNG files, dng:ChannelMultipliers, dng:Green and dng:Temperature. Inspecting the files with Imagemagick showed the raw files to be darker (as expected for gamma 1) but Imagemagick reported the gamma as 0.454545 for all files. The second sample follows a similar pattern: raw.dng 124159636 119M ZIP The second pair are uncompressed TIF and the third is compressed TIF. The first pair were saved as DNG, the one with -R- in the name is raw. The first summarised like this: 293936902 281M -0001.dng Zip I performed some tests with two 48bit sample scans taken at 2400dpi. I would like to understand the differences between the formats to help decide the best choice for archival storage. The vuescan application supports saving scans DNG and TIFF format which can be processed and/or what it calls raw.
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