4 Replies Latest reply on Mar 29, 2011 6:58 AM by jaap_bouma

    Vuescan DNG problem

    jaap_bouma

      Hi all,

       

      I am having a problem with DNG's generated in Vuescan. I have a substantial amount of scans saved out as Vuescan DNG.

      I now know this is not very wise if you want to postprocess in ACR and LR, because vuescan DNG's are not real raws. They are rendered untagged files, this is why you don't want to process them in ACR and LR.

       

      Not wanting to rescan many strips of film I decided to open them in Vuescan and save them out as tagged (prophoto and gray(for B&W)) TIFFs for postprocessing in ACR/LR.

      However here comes the problem, the DNG's show up in Vuescan as only 300dpi (originally scanned at 4000dpi) and the resulting TIFF is very tiny and unusable (pixilated). These DNGs have been opened before in ACR and/or LR.

       

      According to Ed Hamrick, the author and maintainer of Vuescan, once opened in ACR/LR a tag is written into the DNG, c716 for ACR and c717 for LR alongside a low res preview (despite rendering a 1:1 preview). This is causing Vuescan to only see a low res preview at 300dpi (my ACR workflow setting). Ed is not able to give a solution and regards these DNG's as being manipulated. Maybe Vuescans implementation of DNG is defying the purpose of DNG being an archival file format, but that is not solving my problem right now.

       

      Is there a way to strip off all the tags and preview(s) written into the DNG to return the Vuescan DNG into its pristine state before opening into ACR/LR, because these untouched DNG properly show up as 4000dpi files in Vuescan.

       

      Any help is greatly appreciated

       

      Regards,

       

      Jaap

        • 1. Re: Vuescan DNG problem
          sandy_mc Level 3

          You could try ExifTool to delete tags, but you will be shooting in the dark as you won't really know what Vuescan considers to be pristine.

           

          But I don't understand your comment about not wanting to process the DNGs in LR or ACR. So far as I am aware, both process all DNGs, raw or not, just fine.

           

          Sandy

          • 2. Re: Vuescan DNG problem
            jaap_bouma Level 1

            Hi Sandy,

             

            Thank you for your answer. I ll give it a try.

            The reason you don't want to process vuescan dng's in ARC/LR is that these dng's are rendered files as opposed to real raw files which have te be demosaiced in the raw converter.

            Vuescan dng's behave much like a tiff, but they are untagged and ACR/LR assumes sRGB when the file is opened and with all under the hood conversions the result is not what you would get if you open proper tagged TIFFs.

            I remember Andrew Rodney explaining this very clearly but unfortunately i m not able to recall where i once read it.

             

            Jaap

            • 3. Re: Vuescan DNG problem
              sandy_mc Level 3
              Vuescan dng's behave much like a tiff, but they are untagged and ACR/LR assumes sRGB when the file is opened and with all under the hood conversions the result is not what you would get if you open proper tagged TIFFs

               

              Not the case any version of LR or ACR I know of. E.g. pcdMagic creates linear DNGs in what is the equivalent of the ProPhoto space, and LR/ACR reads them fine. (I say "equivalent of" because DNG files don't have tags in the sense that TIFF does, but you can implicitly set the primaries, etc just as you would in a color space tag).

               

              Sandy

              • 4. Re: Vuescan DNG problem
                jaap_bouma Level 1

                I think I may have found what seems to be at the root of the problem.

                Apparently Vuescan writes and reads 1.1 DNG's.(according toExifTool). As soon as such a file is edited in ACR/LR a new DNG (1.3) is written. This 1.3 spec DNG is only opened in Vuescan as its preview (small size @ 300 dpi).

                Unless there is a way to revert a 1.3 DNG to a 1.1 DNG I am stuck. I already tried to use the DNG converter to use a custum setup to have it write DNG 1.1 uncompressed.

                But still no luck, Exif tool reports they still are 1.3 DNG's.

                 

                Jaap