22 Replies Latest reply on Sep 21, 2018 7:56 AM by Todd Shaner

    Why are preview files so large?

    floatingby Level 1

      I opened 2 folders of images, they total 563 GBs of Nikon 14 bit RAW data. The first I set to build 1:1 previews, then seeing how large the preview folder was skyrocketing, the next I set to embedded previews.

       

      Still, the preview image folder grew to 124 GBs!

       

      Ok, that don't make sense to me. why would previews be 1/4 the size on disc of 14 bits RAW images? Full size jpg usually are about 10~15 time smaller.

       

      Given that, how can i reduce the size on disc while maintaining preview good enough to make good edit decision? Is that possible?

        • 1. Re: Why are preview files so large?
          Sahil.Chawla Adobe Employee

          Hi there,

           

          Could you please try the steps mentioned on this article and see if it helps? Optimize Lightroom performance

           

          Regards,
          Sahil

          • 2. Re: Why are preview files so large?
            dj_paige Level 10

            Instead of 1:1 previews, choose standard previews or minimal previews. 1:1 previews depends on the other setting you can choose which is the resolution of the previews, and if you choose a big number there, your previews take up lots of space.

             

            Of course, the tradeoff is if you choose standard previews or minimal previews, then some Library Module actions are slower.

            • 3. Re: Why are preview files so large?
              Laura Shoe Adobe Community Professional

              Lightroom builds up to three JPEG previews for each image - thumbnail size, standard (screen) size, and full size / 1:1. These are used in the Library module, and for previewing in the output modules (not for building final output.) This way Lightroom doesn't have to constantly read all your raw files in order to display them.

               

              You can change how large the standard previews are, whether they are high, medium or low quality JPEGs (I choose medium), and also, how often Lightroom discards the 1:1 previews (which are only needed for zooming in in the Library module.  Go into Edit (PC) or Lightroom (Mac) > Catalog Settings, and click on the File Handling tab. I choose to discard the 1:1 previews one week (after I import them), since I am done editing them at that point. (Lightroom will rebuild any previews you have discarded if/when you zoom in on the photo again.

               

              You can also discard 1:1 previews by going to Library>Previews>Discard 1:1 previews.

               

              Note that when you edit, LR is reading and rendering the raw file - so you're not making editing decisions using the previews.

              • 4. Re: Why are preview files so large?
                Laura Shoe Adobe Community Professional

                Looks like @dj_paige and I were answering at the same time.  The Import choices are really a choice of "build right away upon import" vs. build later as you need them. If you choose Minimal as you import, Standard previews will be built as you view the photos in Loupe view (and you may see the "Loading" message), and 1:1 previews will be built if/when you zoom in.

                • 5. Re: Why are preview files so large?
                  floatingby Level 1

                  Had to change my setup considerably. Previews were by default to 3440(my screen is 1440 x 3440), so I reduced that to 2048(photos are 3 x 2 so (1440/2)*3=2160 pixels minus the interface should be close). Then I set the quality to medium. I'll see how it goes, thanks.

                   

                  Still, considering the RAW images are 8,288 x 5,520 I don't understand why previews are so gigantic. I had to move my catalog from an SSD I wanted to use, because it's blindingly fast, to data storage because the SSD filled up in seconds while building previews. Guess you can't win the speed game.

                  • 6. Re: Why are preview files so large?
                    KR Seals Level 3

                    if you are using a desktop, the solution is to install a separate large sad for your LR catalog, previews and adobe camera raw cache

                    • 7. Re: Why are preview files so large?
                      floatingby Level 1

                      Right now I left the Lightroom cache on the 256 GB SSD which I thought of using for my catalog; I moved the catalog to a 2 disc, 4 TB raid 0 array which is where all my data live, while Lightroom itself is installed on the same M.2 drive as the operating system. Not ideal because that raid array is half the speed of the SSD, but still above well 300 MB/s R/W.

                       

                      The only other drives I have access to is the 24 TB file server, but that's over a gigabyte network so only about 112 MB/s.

                      • 8. Re: Why are preview files so large?
                        KR Seals Level 3

                        If you don’t have space for an additional ssd, I would upgrade the os ssd to 1 TB and keep everything but th image files themselves on the ssd.

                        • 9. Re: Why are preview files so large?
                          floatingby Level 1

                          Ok, discarded the previews I`d already built, rebuilt the previews of a folder of images set to 2048 at medium. Still ended up with a preview folder on disc size of 98 GB, when the original files folder is 283 GB so... It`s worst than before! Now it takes roughly a third the disc space of the RAW files.

                          This doesn't make a lick of sense to me. The RAW files are 8,288 x 5,520 pixels 14bit uncompressed, why in the name of all that is holly would 2048 x 1365 compressed jpg preview files take a full 1/3 of that? Especially considering it took hours to build on a fast, modern computer so it should be highly compressed?

                          Something isn't right here.

                          • 10. Re: Why are preview files so large?
                            D Fosse Adobe Community Professional & MVP

                            Indeed. Those sizes are crazy, something's not right here. But what? Let's look at some real file sizes.

                             

                            • My Sony a7RII files are 7952 x 5304 pixels, 14 bit uncompressed. The raw file is 42 MB.
                            • A full-size 1:1 jpeg, at quality 8, weighs in at 3.9 MB. This is a fairly average, mid-busy image, so it should produce an "average" jpeg file size.
                            • Reduced to 2048 pixels long side, jpeg file size is a mere 289 kB, still at quality 8.

                             

                            Off the top of my head, that means the jpeg preview should be about 0.7 % of the original raw file size.

                            • 11. Re: Why are preview files so large?
                              floatingby Level 1

                              Yep, size on disc for my particular example should be around 1 to 1.5 GB, not 98 GB. Something is broken in Lightroom.

                              • 12. Re: Why are preview files so large?
                                bob frost Level 3

                                I think you are forgetting what Laura said above - that a preview file is a collection of previews of different sizes, and I would add that if you have face recognition on, then you have another preview file for the same image with the faces on. I have 175,000 images occupying about 3.5 TB and the preview folder is about 400GB (with only a few 1:1s). That is normal as far as I know.

                                 

                                Bob Frost

                                • 13. Re: Why are preview files so large?
                                  floatingby Level 1

                                  I'm not forgetting anything at all. A jpg of 2048 resolution at medium quality(exported from Lightroom no less) is 40 time smaller on disc than the corresponding full size RAW file. So even IF Lightroom generate a few of those, no way the preview folders should skyrocket to 1/3 the size of the corresponding RAW original file folder, the math just does not add up.

                                   

                                  [EDIT]Oh, not using face recognition at all; not that it should matter in this case anyway. And you have about 9:1 ratio, better than what I'm getting, but still completely awful.

                                  • 14. Re: Why are preview files so large?
                                    D Fosse Adobe Community Professional & MVP

                                    I still agree with the OP, this can't be right. It defeats the whole purpose of using previews - then you might just as well read directly from the raw files.

                                     

                                    (and now I'm off to take a look at my own previews).

                                     

                                    EDIT - 3TB raw files, 34 GB previews - 2048 at high quality and 1:1 discarded after 1 day. That's more like it.

                                     

                                    EDIT 2 - hold on, I think I deleted the whole previews folder a while ago, can't recall when. So that figure doesn't mean much.

                                    • 15. Re: Why are preview files so large?
                                      bob frost Level 3

                                      You are assuming that the previews are normal jpgs. Are they? I've seen it written that smart previews are partly-processed raw files. Not seen any statement about the ordinary previews. My preview files vary in size from 30KB to 34MB. . My acr cache files (used in Develop) take up another 200GB! You haven't mentioned them.

                                       

                                      Buy a bigger disk to store them all on. They are so much cheaper than they used to be.

                                       

                                      Bob Frost

                                      • 16. Re: Why are preview files so large?
                                        floatingby Level 1

                                        Not using smart preview.

                                         

                                        Normal HD are cheap now, yes, but they`re also very slow, even in RAID array. Fast SSD are still extremely expensive and not that large(yes there are cheap SSD`s, but they are neither fast nor reliable).

                                         

                                        But that`s beside the point. Right now the file preview system make no sense to me, at all. Why use a separate preview file if it`s just as large a file as the original, therefore just as slow to load? Or is the program broken?

                                         

                                        Anywho, I'll try to make Lightroom NOT make any previews, or if I can't then make them the smallest possible and see where that gets me.

                                        • 17. Re: Why are preview files so large?
                                          Laura Shoe Adobe Community Professional

                                          I can't speak to the size of the Previews file, but to minimize preview building, you can choose Embedded and Sidecar in Import, and the LR Library module will use the preview that your camera has embedded in the raw file. However, this may well look different from LR's rendering and may be smaller than the full-size file, and as soon as you edit a photo, LR will move to building its own Standard preview. In the meantime, LR still has to store the embedded preview in the Previews file.

                                           

                                          If you scroll down in this blog post you'll find a video tutorial on the Embedded Preview workflow.

                                          • 18. Re: Why are preview files so large?
                                            bob frost Level 3

                                            "Right now the file preview system make no sense to me, at all. "

                                            .........................................................................

                                             

                                            Maybe that's because you aren't a software engineer! Nor am I, but I don't have to understand everything in order to use it.

                                             

                                             

                                            "Why use a separate preview file if it`s just as large a file as the original, therefore just as slow to load?"

                                            .......................................................................................... ................

                                             

                                            Probably because as Laura and I have said, the preview file for an image is NOT one single preview, it is collection of different sized previews for use in the filmstrip, library grid with different sizes, library loupe with fit to screen or fill screen, print views, web views, etc. Adobe describe it as the preview 'pyramid'; each preview in the file being a bigger or smaller horizontal slice of a pyramid.

                                             

                                             

                                             

                                            "Normal HD are cheap now, yes, but they`re also very slow, even in RAID array. Fast SSD are still extremely expensive and not that large(yes there are cheap SSD`s, but they are neither fast nor reliable)."

                                            ...................................................................

                                             

                                            Some experts state that the speed of the disks does not have much effect on LR; it is far more dependant on the speed of the CPU to process everything on-the-fly: even your rendered previews need processing to fit on the particular bit of your size of screen. Drag the slider on the Library Grid and the images get bigger or smaller more or less instantly. Widen the side tool sections of the Develop screen and the image gets bigger or smaller.

                                             

                                            Bob Frost

                                            • 19. Re: Why are preview files so large?
                                              Todd Shaner Adobe Community Professional & MVP

                                              floatingby  wrote

                                               

                                              Right now the file preview system make no sense to me, at all. Why use a separate preview file if it`s just as large a file as the original, therefore just as slow to load? Or is the program broken?

                                              I suggest running your own check on preview file size. Create some new 1:1 and Standard using separate files then check the .lrprev file size using Finder or Windows Explorer with Search on Date = Today in the LR Previews folder (see below).

                                               

                                              Here's a Canon 5D MKII 21 megapixel raw file that is 28 MB. The 1:1 preview file is 5.5 MB (1/5 size), the 2560 px Standard preview file is 1.2 MB (1/23 size) using 'Medium' Preview Quality setting. For comparison a full-size 70 Quality JPEG Export of the same image file is 3.8 MB. The 1:1 .lrprev file is larger because it contains an image pyramid with 1:16, 1:8, 1:4, 1:2, and 1:1 Previews. Your results should be similar.

                                               

                                              EDIT: Note that the Standard and 1:1 previews appear to use two separate files probably to allow discarding 1:1 previews without having to rebuild Standard previews. So you need to add them together to determine the total Previews overhead. High ISO images that have a lot of visible noise due to insufficient NR and/or over-sharpening will increase the Standard and 1:1 preview file size by a factor of 2X or more. Just an FYI on keeping the Previews folder from bloating!

                                               

                                              • 20. Re: Why are preview files so large?
                                                floatingby Level 1

                                                Oooooh, so it also build 1:2, 1:4, 1:8 etc previews ahead of time? Well that explains a lot.

                                                 

                                                The whole point of course was to try to optimize and speed things up, but it seems no matter what I do I'm just exchanging four quarters for a dollars.

                                                 

                                                Thank you people for dealing with my questions.

                                                • 21. Re: Why are preview files so large?
                                                  bob frost Level 3

                                                  Hi Todd,

                                                   

                                                  "Note that the Standard and 1:1 previews appear to use two separate files probably to allow discarding 1:1 previews without having to rebuild Standard previews."

                                                  .......................................................................................... .....

                                                   

                                                  Are you sure about that? My impression is that when you create a 1:1 preview, LR deletes the old preview pyramid file and creates a new file with 1:1 included. LR has to update the folders and preview and root-pixel.dbs.

                                                   

                                                  I've just selected a folder of 69 images out of my 170K images and created 1:1 previews for them. After waiting quite a while for all read/write transactions to finish (watching with Resource Monitor), the total number of previews has not changed - I just have 69 new preview files with today's date on them...

                                                   

                                                  Bob Frost

                                                  • 22. Re: Why are preview files so large?
                                                    Todd Shaner Adobe Community Professional & MVP

                                                    https://forums.adobe.com/people/bob+frost  wrote

                                                     

                                                    Hi Todd,

                                                     

                                                    "Note that the Standard and 1:1 previews appear to use two separate files probably to allow discarding 1:1 previews without having to rebuild Standard previews."

                                                    .......................................................................................... .....

                                                     

                                                    Are you sure about that? My impression is that when you create a 1:1 preview, LR deletes the old preview pyramid file and creates a new file with 1:1 included. LR has to update the folders and preview and root-pixel.dbs.

                                                    Thanks Bob–You are absolutely correct! I was just looking at the small sample test files and had a Senior moment. If the 1:1 and Standard previews we're separate files then you'd have 2X+ preview files in the Previews.lrdata folder. I have a catalog with 36,748 image files and 38,484 files in the Previews.lrdata folder. The 1,736 additional preview files are most likely for for virtual copies.