6 Replies Latest reply on Feb 18, 2008 4:26 AM by (Erwin_Vanderhoydonks)

    ACR calibrate tab and Vuescan DNG

    Joseph Elfelt Level 1
      Having ordered a Nikon Coolscan V ED scanner to digitize ektachrome slides, I am now busy reading and thinking about how to best to include scanned pics in my workflow. Note that one key element of my workflow is to do as much as possible in ACR per the teachings of Bruce Fraser, Jeff Schewe and others. The current ACR 4.x is more than just a raw converter.

      I realize that I can make a custom profile for my scanner. However, ACR does not use scanner profiles or camera profiles. Instead, ACR provides the calibrate tab to accomplish the same purpose. Has anyone calibrated their scanner as follows and if so, do you have any tips/suggestions to share?

      1. Use Vuescan professional to scan an it8 target. One source for reasonably priced targets is Wolf Faust, http://www.targets.coloraid.de/

      2. Tell Vuescan to output the scan as a DNG. Yes, I know this is not a true raw image.

      3. Open the DNG in ACR and go through the calibration process. If you are not familiar with this process, here is a description by the late Bruce Fraser. http://www.creativepro.com/story/feature/21351.html
      Of course Bruce was describing the process for using ACR to calibrate a camera, not a scanner. Fortunately, the principles are the same. The color patches on an it8 target are supposed to conform to a standard and you receive a file stating those color values when you buy the target. The goal then is to scan your target and then use the ACR calibrate tab to tweak the colors of the scanned image so they are as close to the standard colors as possible.

      4. To help with step 3, Rags Gardner has posted a CS script for it8 targets at http://www.rags-int-inc.com/PhotoTechStuff/ColorCalibration/
      This script does not do the calibration for you but instead it reads the color values in your scanned target and produces a report showing the color values in your scanned target and the standard color values you are trying to get close to via the calibration process.

      5. Save the result of the scanner calibration and recall it whenever using ACR to process DNGs produced by the same scanner and Vuescan.

      Does this make sense?
      Anyone tried it?
      Can the ACR calibrate process work with a Vuescan DNG?
        • 1. Re: ACR calibrate tab and Vuescan DNG
          michael shaffer Level 1
          I don't understand why you would need the intermediate ACR step(?) That is, calibrate Vuescan the usual way, and save it as a TIF. Then, run Rags' script on the TIF.

          Actually, if Vuescan's own calibration process worked properly, there would (ideally) be no need to calibrate again.
          • 2. Re: ACR calibrate tab and Vuescan DNG
            michael shaffer Level 1
            > Then, run Rags' script on the TIF ...

            Oops! ... that wouldn't do much good. I also confused the color targets reccommended for each ... IT8 for Vuescan and the Macbeth CC for the ACR script. Now your question makes a bit more sense ... but it does combine 2 softwares, only one of which needs to be calibrated.

            You can however, obtain an IT8 slide and use that for calibrating Vuescan.
            • 3. Re: ACR calibrate tab and Vuescan DNG
              Rags Gardner Level 1
              Joseph,

              My first reaction is that I would recommend traditional profiling for scanners and skipping ACR completely. That said, I enabled TIF scanner support as a result of a request from another user. He indicated he was satisfied with the results. The ACR calibration script does calibrate. With the proper target datasheet, it can be used with negatives. The read colors script merely reports the target/image differences. The DNG step should be unnecessary.

              Since this is somewhat new territory with CS3, I would be willing to work with you offline to see if we can accomplish something that fits your workflow. Contact me via my web site.

              As a TIF image, I would expect ACR to honor whatever image profile was already tagged on input. Thus, ACR could be used simply for aesthetic tweaking and things like cropping. I must admit I have not tested this thoroughly. It might be treating it as untagged raw values? If so, I have a lot of questions about what ACR does with JPG images.

              If ACR is ignoring the TIF profile, it could explain why Vuescan is not giving you the results you expect. Have you run a target through Vuescan profiling, saved it as TIF, then just run read colors to evaluate the results? Then do the same after opening in ACR with everything defaulted.

              Cheers, Rags :-)
              • 4. Re: ACR calibrate tab and Vuescan DNG
                Level 1
                >I would expect ACR to honor whatever image profile was already tagged on input.

                Pretty sure that's what it does with all supported rendered files with profiles...if the file does NOT have a profile (no embedded profile), I'm pretty sure it assumes sRGB...
                • 5. Re: ACR calibrate tab and Vuescan DNG
                  Joseph Elfelt Level 1
                  Rags and Jeff,

                  Thanks much for taking the time to reply. Indeed what I have described is a bit of a new approach made possible by the ability of the current ACR to read TIFF and/or the ability of the current Vuescan software to output a DNG.

                  I shall poke at this a bit and report back. Sadly, my investigations are on hold pending arrival of a motherboard replacement.
                  • 6. Re: ACR calibrate tab and Vuescan DNG
                    Thanks for the workflow and The links. I will let you know my results...