6 Replies Latest reply on May 25, 2015 4:25 PM by Parris37

    Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?

    Parris37 Level 1

      I've scanned a couple of hundred old black and white negatives using Vuescan to 16-bit grayscale TIFFs. If I open these in Photoshop CC2014 the tab indicates they are a single 16-bit gray channel. But if I have Lightroom convert these to DNG, then open them in Photoshop, they appear as 48-bit RGB, or three 16-bit RGB channels. All three channels are identical. What is happening here? Is it just being rendered as a 48-bit RGB image byPhotoshop or is the DNG itself storing the image as RGB? The DNG is not much larger than the TIF so it doesn't appear to be storing 48-bits of information. Am I losing any data by going to DNG with a grayscale scan?

       

      Since I can export the dng back to a tif and it returns to a single grayscale channel of 16-bits, I guess I'm not losing any information, but would I be better off not using DNG for grayscale scans? Or should I just edit in Photoshop with all three RGB channels turned on and figure that I'm editing the grayscale channel should I ever export back to tiff?

       

      It seems at the least there's a shortcoming in the rendering of grayscale DNGs into Photoshop?

        • 1. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
          Per Berntsen Adobe Community Professional

          There is no advantage in converting these tiffs to dng, it doesn't turn them into raw files, so just leave them as tiffs.

          So, just import them in LR, do your work on them, and export as necessary. LR can only export RGB files, so you may want to open them in PS and convert to grayscale after exporting.

          • 2. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
            Per Berntsen Adobe Community Professional

            I should add that if you export jpgs, there is usually no need to convert them to grayscale - the file size will be roughly the same, since the three channels are identical.

            Furthermore, for best results, jpgs for the web and general screen viewing should be RGB, and have the sRGB profile embedded.

            • 3. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
              Parris37 Level 1

              Thanks for the replies. If I can comment:

              1. When you say LR can only export as RGB, does that include "'exporting' into Photoshop for editing"? It seems Lightroom only opens grayscale tifs OR dngs as RGBs in Photoshop. Even without any develop settings applied.

              2. An advantage to going from tif to dng would be seeing updated previews in LR of my develop settings.

              3. The downside of DNG (not as easily viewable outside LR) seems minimal, as both 16-bit-grayscale tifs and converted 16-bit-grayscale DNGs [I assume it's 16-bit because the file size is about the same], once opened in Photoshop and resaved as new TIFs, BOTH convert to 16-bit RGB and the file size increases accordingly. Here are my results:

               

              Original 16-bit gray TIF (LZW):              68MB          After DNG conversion: 41MB   (Gray/16)

              Open TIF in PS, save as TIF:               153MB             DNG saved as TIF: 153MB   (RGB/16)
              Reopen (apply Image/Mode/Grayscale),

                                                     resave as TIF:  71MB                                              72MB    (Gray/16)

               

              So what about this possible workflow? Import 16-bit TIFs to LR; convert to DNG; apply develop settings to DNG in LR and update previews; edit DNGs in Photoshop and save as TIFs BUT always convert to (Image/Mode/Grayscale) grayscale before saving and closing.  Upside of DNG: updated previews. Overall downside: must always add grayscaling step in Photoshop to keep file sizes manageable.

               

              Would you agree LR would be a better product if it would open (and export) grayscale images without converting to RGB? I can see an option for RGB when Web export is desired, but to always go to RGB without choice and triple the size of each iteration of an edited file is a wasteful and requires remembering to apply grayscaling each time in PS. Also, there's nothing to keep me from inadvertently meddling with the RGB channels once the files are open in PS, unless one would want to do that for special toning effect (and if so wanted, one could instead convert a grayscale opened in PS to RGB from within PS).

              • 4. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
                trshaner Adobe Community Professional & MVP

                Parris37 wrote:

                Here are my results:

                 

                Original 16-bit gray TIF (LZW):              68MB          After DNG conversion: 41MB   (Gray/16)

                Open TIF in PS, save as TIF:               153MB             DNG saved as TIF: 153MB   (RGB/16)
                Reopen (apply Image/Mode/Grayscale),

                                                       resave as TIF:  71MB                                              72MB    (Gray/16)

                Try saving the 16-bit Grayscale TIFF with ZIP Compression. It will probably be very close in size to the DNG conversion. I do color film scans to TIFF file format and the upside is that you can use adjustments layers. I process the TIFF in PS for dust spot removal and other destructive editing, and then back in LR for toning and color correction. No need to reexport the file. I've recently started doing film scans using a DSLR copy setup, but I still export the file to TIFF for processing in PS:

                 

                https://luminous-landscape.com/scannerless-digital-capture-and-processing-of-negative-film -photographs/

                • 5. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
                  Per Berntsen Adobe Community Professional

                  I think the best way to reply here is to explain my own workflow.

                  I have to be a bit brief - it's getting very late, and I'm starting a six week roadtrip tomorrow.

                   

                  I do a lot of work with scanned tiffs, and it never occured to me to convert them to dng.

                  I start out with rough tonal adjustments, noise reduction, and retouching in PS, and then import the image (with all shadow and highlight detail present) in LR.

                  There I do fine tuning and capture sharpening, but sometimes the image has to go back to PS for editing. I then use Edit Original, and the image opens in grayscale in PS. After saving in PS, I click the exclamation mark on the thumbnail, and choose Import settings from disk, and the images updates in LR.

                   

                  Since I find LR's output sharpening unsuitable for scanned images (it's probably optimized for digital capture), I export a new tiff from LR, open it in PS, convert from RGB to Grayscale, and use Smart Sharpen for output sharpening. I sure wish LR could export grayscale, but I've learned to live with it. You could easily set up an action converting to Grayscale (and to 8-bit), and use it routinely.

                   

                  My knowledge of the technicalities of dng files is limited, but my impression is that they are grayscale files, which explains the small filesize.

                  The color is added in the deconvolution process in LR.

                  I don't think your workflow with convertin to dng will affect quality, so stick with it if you like.

                  I'll be happy carry on this discussion, but since I'll be on the road, replying might take some time.

                  • 6. Re: Converting a 16-bit grayscale tif scan to dng and getting 48-bit RGB?
                    Parris37 Level 1

                    Thanks so much for explaining your workflow, it sounds similar to what I plan to do. I might just stick with the .tifs after all. With a set of originals set safely aside, it makes sense to do spot and dust corrections as .tifs before importing into LR, and then Develop there. Whether developing makes the conversion to dng worthwhile remains my question to work with in practice. It might be as easy to 'bake in' a mostly one-time Develop step by saving the developing to another tif copy, stack that on top of the pre-develop, and my 'preview' is updated that way without the dng. I could even import the blemished tif into LR first, clean it in Photoshop as a copy and stack that on top, then develop and save out as a third copy to be stacked on top again. That should give me the ability to restart from 3 points: original, cleaned, or developed, without dipping into the dng format. You've given me a good start to try out some scenarios here, thanks again.