25 Replies Latest reply on Feb 16, 2009 1:55 AM by PECourtejoie

    What good are the preview JPEGs? (newbie question)

      Dear Folks,

      I'm new to converting raws to DNGs, and I can't seem to find any use for the preview JPEGs that DNG converter can embed in the file.

      Mac OSX (10.4.11) doesn't display them in Finder windows (Icon view mode). Get Info windows can show me a small preview whether or not I embed a JPEG. Mac OSX's Preview program can't display DNG files whether or not JPEGs are embedded in them. I don't see any difference in the functionality of Bridge and Photoshop whether they're there or not.

      That pretty well describes my entire photo workflow, so if previews really are irrelevant to it, seems to me I might as well leave them out and save a little processing time and disk space.

      Am I missing something obvious? (probably)

      Thanks!

      Ctein
        • 1. Re: What good are the preview JPEGs? (newbie question)
          PECourtejoie Adobe Community Professional
          Ctein, something is not normal, as Preview in Tiger is supposed to display DNGs correctly: http://www.barrypearson.co.uk/articles/dng/products.htm
          I remember some "raw format" updates to Os X, look on Apple's website.
          What version of what software did you use to create the DNGs?
          • 2. Re: What good are the preview JPEGs? (newbie question)
            Level 1
            Dear PE,

            Hmmmm. Suspected might be such.

            Still on CS3 for Bridge/Photoshop, but running latest version of DNG Converter (5.2.0.65) as a stand-alone.

            MacOS is at 10.4.11, version of Preview is 5.2.0.65, iPhoto is at 7.1.

            Numerous sources, including Apple's website, confirm that these versions of iPhoto and Preview *SHOULD* be able to handle the DNG files. Strong implication, reading Apple's notes on Tiger OS updates (which I'm current on), is that this capability is inherent in the standard build (the updates fixed display glitches, didn't add the capability).

            OK, maybe someone else can solve THAT mystery.

            Meanwhile, simpler question: how big are the "medium" size preview JPEGs in DNG files (pixel dimensions. percent of original file dimensions, whatever units are appropriate)?

            Thanks!

            pax / Ctein
            • 3. Re: What good are the preview JPEGs? (newbie question)
              PECourtejoie Adobe Community Professional
              Ctein, try those updates:
              http://support.apple.com/kb/index?page=search&src=support_site.kbase.search&locale=en_US&q =Digital%20Camera%20Raw%20Compatibility%20Update

              (you might need to patch the link together)

              As for the Medium size jpgs, the only reference I've found lists a max size of 1024px in one direction for medium size previews, but it is not from an Adobe source.

              By the way, thanks for all the enlightening articles that you create!
              • 4. Re: What good are the preview JPEGs? (newbie question)
                Level 1
                Dear PE,

                Thanks for the compliment on my articles. Wait'll you see my new one later today for The Online Photographer, about how many pixels a digital camera could make effective use of. Scary!

                This DNG/OS X business is a real puzzle. I'd previously checked out the info you linked told have and couldn't find any update that addressed this I don't have (in fact, a number of them strongly imply that I should have DNG support, regardless).

                The fact that I don't in either Preview or iPhoto argues for something at the OS level. But what???

                Be nice to get this fixed.

                pax / Ctein
                • 5. Re: What good are the preview JPEGs? (newbie question)
                  PECourtejoie Adobe Community Professional
                  Or maybe could it imply a support for DNG 1.1 and not the latest one? But AFAIK, there is no change in the handling of the thumbnail, and DNG support is supposed to be seamless.

                  You could try downloading an older version of the converter to check if Preview can, erm... preview it.

                  Pierre-Etienne.
                  • 6. Re: What good are the preview JPEGs? (newbie question)
                    Level 1
                    Dear P-E,

                    Yeah, I can't see any compatibility issues either, on paper anyway.

                    I did already try making a DNG from within Adobe Bridge/ACR CS3, which is the oldest version of the converter I have. It didn't open with Preview/iPhoto, either.

                    I think that unless someone else has a clearcut answer, I'm going to stop worrying about it. Not like I had medium-res previews of my raw files, so I'm no worse off. Presumably when I upgrade to Leopard/Snow Leopard, which ain't all that far off, it'll become a non-problem.

                    (famous last words).

                    Oh well, another day, another learning curve.

                    pax / Ctein
                    • 7. Re: What good are the preview JPEGs? (newbie question)
                      Panoholic Level 2
                      > Get Info windows can show me a small preview whether or not I embed a JPEG

                      That is the thumbnail, not the preview.

                      > Mac OSX's Preview program can't display DNG files whether or not JPEGs are embedded in them

                      I know nothing of Mac, but I would try to rename a DNG to TIF or TIFF and see if the Preview program accepts that or not. If it works, then the problem is with the file name extention; if it does not work as TIF either, then the problem is with the file structure, though I would not know what.

                      Have you tried it with "small JPEG preview" as well? If you specify "large", then the DNG converter generates *both* a small and a large preview (beside the thumbnail); it is not impossible, that your program becomes confused by the presence of two previews (though this is really far fetched).
                      • 8. Re: What good are the preview JPEGs? (newbie question)
                        Level 1
                        I believe the standard respose here when the roles are reversed would be to say "Buy a PC," but I don't think I'll make that recommendation.

                        Why not file a bug with Apple? Perhaps it is the distraction of having a reputation for producing music players these days than for being the platform of choice for creative professionals as in days of old, but Apple lately has become Microsoftian in its dedication to supporting DNG and other RAW formats. In Apple's implementation of DNG support, they completely give up if they don't like your camera model or some other attribute of the RAW data. Apple does the same thing with Canon sRaw files.

                        Microsoft has more or less the same thinking in its WPF bridge to WIC.

                        The idea behind the JPEG preview is that even if you can't decode the RAW data, then a quickly rendered JPEG preview is available for all DNG files, and it's always easy to find and provide a view of the file's contents. I don't think you should blame DNG for Apple's poor support for photographers.
                        • 9. Re: What good are the preview JPEGs? (newbie question)
                          Level 1
                          Dear David,

                          Nobody's blaming anyone for anything. Certainly not me. Are you?

                          pax / Ctein
                          • 10. Re: What good are the preview JPEGs? (newbie question)
                            Level 1
                            The statement "What good are the preview JPEGs?" lead me to believe that the implication was that these were of questionable use. The tone seemed to be a knock at the value of DNG, or at least one of its most compelling features that it inherits from TIFF/EP.

                            In the world of Digital Asset Management, which is just about everywhere in your work flow where you aren't editing the RAW image, the JPEG preview image should be of great use, as should the thumbnail. It's sad that in practice this often isn't the case, and I expect more from Apple.
                            • 11. Re: What good are the preview JPEGs? (newbie question)
                              Ramón G Castañeda Level 4
                              The previews of DNG files show perfectly fine on my Macintosh.
                              • 12. Re: What good are the preview JPEGs? (newbie question)
                                Level 1
                                Dear David (and Ramon),

                                Nope, no such implication whatsoever. I entirely understand the theoretical benefit. I've just been trying to find out if they'll benefit me.

                                BUT... here's an unexpected curiosity. I just ported one of my freshly-baked DNG file to a friend's brand new Mac, so it's running the latest versions of everything and it ought to be pretty much a stock configuration.

                                It can't read my DNG preview JPEG, either! When I drag the DNG file into the Preview app, it shows me a question mark, not a preview! I just double-checked, and I am generating the DNGs using the default settings in Adobe DNG Converter (medium JPEG, lossless compression, non-linear, no embedded RAW, etc.)

                                So, what's going on?! Ramon confirms that DNG previews should be viewable under Mac OSX. Either I'm doing something wrong (entirely likely) or there's something broken in A-DNG-C.

                                The DNG files I'm generating look perfectly fine in Adobe Bridge/ACR/Photoshop, by the way. It's something hinky with the JPEGs.

                                Anybody got a clue? I'm fresh out!

                                pax / puzzled Ctein
                                • 13. Re: What good are the preview JPEGs? (newbie question)
                                  Level 1
                                  Many apps which claim to support DNG miss the point I was trying to raise. Even though DNG is a file format where the viewer need not know the internals of the camera to produce an image from the RAW data in many cases, and in all cases they should be able to use the thumbnail and the preview (which is just a standard JFIF stream), many simply give up completely if there is something about the camera model, RAW data, or supporting details that they don't like.

                                  What model of Camera did the DNG come from, and can Preview display the source file on your version of Mac OS?
                                  • 14. Re: What good are the preview JPEGs? (newbie question)
                                    It's a fair point - I don't have any DNG from cameras not supported by Apple's raw support, so I can only speculate but that sounds likely to be the problem.

                                    I double-checked and all the DNGs I've collected, from my 10D, 20D, G9, and a Nikon D2x, work just fine in Finder previews, Preview, etc.

                                    At least for Finder previews it *would* be nice if they used the embedded preview, so it would closely match the corrections applied in ACR/LR, but for Preview and Aperture I'm resigned that they won't match since they start back with the raw data, and don't use the same processing parameters as ACR/LR.

                                    Underlying all of this is the general wish, however unrealistic, that editing parameters were portable between RAW engines. Not gonna happen, at least no time soon, but it does make me wish there was a standard, a la ICC, to define the transformations in a vendor-neutral way.
                                    • 15. Re: What good are the preview JPEGs? (newbie question)
                                      Level 1
                                      Dear Dave and Roger,

                                      Hmmm, I hadn't thought abut the camera model. I don't see why that should affect display of the preview JPEG that's wrapped into the DNG file, but it's a fair question. I know I've got some Nikon D200 raws from a camera test around here somewhere. I'll get back to you after some tests.

                                      pax / Ctein
                                      • 16. Re: What good are the preview JPEGs? (newbie question)
                                        Level 1
                                        There sort of is a standard, portable way to define some of the transformations/editing commands. The DNG spec includes some XMP tags for this purpose. I don't think many apps besides Adobe's honor these tags. Even if all RAW processing apps recognized these tags, the results would vary since different algorithms yield different results, but at least you would have a more consistent experience.
                                        • 17. Re: What good are the preview JPEGs? (newbie question)
                                          Level 1
                                          Ctein - as I said, it's a problem because those apps - Preview, Finder, iPhoto, etc - don't seem to use the embedded JPEG preview at all. I could be wrong on this, but from what I've observed, these apps always go to the raw data within the DNG to generate display for these files - they never touch the preview.

                                          Why an app can't render a DNG if it doesn't have explicit support for that camera model is another thing, which seems to defy the basic concept of DNG. But some products have this limitation, while others don't.
                                          • 18. Re: What good are the preview JPEGs? (newbie question)
                                            Level 1
                                            Dear Dave,

                                            OK, ran my tests.

                                            Preview and iPhoto can handle both the Nikon raw (NEF) file and the derivative DNG file. Both apps take exactly the same amount of time to open and render the NEF and DNG files.

                                            This leads me to believe that these apps DON'T make any use of the preview JPEG bundled into the DNG file; they just natively understand the two raw formats. Which explains why I'm not seeing anything with the DNGs generated from my camera's files. The apps aren't even looking at the JPEG, and if they can't understand the raw info in one format, they can't in the other.

                                            Makes sense, now.

                                            Takes me back to my original question, or close to it. Is there a list of apps out there that DO make use of the JPEG preview? That'll let me figure out if these are of any use to me.

                                            Thanks for your help!

                                            pax / Ctein
                                            • 19. Re: What good are the preview JPEGs? (newbie question)
                                              MadManChan2000 Adobe Employee
                                              I can't speak for other apps, but Bridge and Lightroom certainly do. It's how they can provide a preview quickly without having to decode the raw data; that's essentially why it's there. I'm pretty sure Photo Mechanic also reads the embedded preview.
                                              • 20. Re: What good are the preview JPEGs? (newbie question)
                                                Level 1
                                                Expression Media has an option to use the embedded JPEG when handling RAW files. I haven't tried this on the Mac version, but I know the Windows version honors this.

                                                Preview on the Mac has the same issue with Canon 40D sRaw files. There is a full sized JPEG preview in the sRaw CR2, but you can't view it with Preview. I can see where Aperture would bail on you if it couldn't understand the RAW data, but I doubt anyone uses Preview to process their RAW images.
                                                • 21. Re: What good are the preview JPEGs? (newbie question)
                                                  PECourtejoie Adobe Community Professional
                                                  Ctein, does the unconverted raw files (can we ask which one?) from your camera show an image in preview? Some cameras seems to be only supported in 10.5, as I gathered from another thread.

                                                  Pierre (pondering about what Angenieux lenses will be required in the future after reading Ctein's article on megapixels on TOP)
                                                  • 22. Re: What good are the preview JPEGs? (newbie question)
                                                    Level 1
                                                    Dear Pierre,

                                                    Based on a highly statistical sample of two [smile], raw and DNG compatibility seem to go hand in hand. If the app can view the raw file, it can view the DNG file; if it can't view the raw, it can't view the DNG either.

                                                    This seems to me to be slightly at odds with the concept of DNG but 'shrug'; such is life.

                                                    BTW, Eric's right that previews load somewhat faster in Bridge because of the embedded JPEGs, but group editing of development settings goes slower, because the whole DNG files need to be rewritten instead of the very small xmp files. So it comes out kind of a wash.

                                                    Anyway, I'm now satisfied I understand how all this works, which is what I wanted before committing to converting everything. Now comes the scutwork.

                                                    Thanks again.

                                                    pax / Ctein
                                                    • 23. Re: What good are the preview JPEGs? (newbie question)
                                                      PECourtejoie Adobe Community Professional
                                                      Indeed, Ctein, DNG format acceptance suffers from this partial implementation of the standard by some third party manufacturers, including operating system creators.

                                                      Still, in my eyes, the real goal of DNG is in-camera generation, the other uses being interesting and useful by-products of the programming skills of Thomas Knoll and his team.
                                                      • 24. Re: What good are the preview JPEGs? (newbie question)
                                                        Ramón G Castañeda Level 4
                                                        >Still, the real goal of DNG is in-camera generation.

                                                        Of which some people lose sight. :/
                                                        • 25. Re: What good are the preview JPEGs? (newbie question)
                                                          PECourtejoie Adobe Community Professional
                                                          Sorry, I edited while you quoted me, but the message is still the same.