4 Replies Latest reply on Jun 14, 2016 12:24 PM by birdgeek

    Does changing the metadata in an exported jpg re-save and degrade the jpg?

    birdgeek Level 1

      In choosing photos for my PhotoShelter website I do the following:

      • I make a collection containing potential choices, edit the collection into final choices.
      • I next export the final selections to jpg formatted for PhotoShelter; the export sends them to a specified folder recognized by LR. LR recognizes the jpgs within the folder and retains the metadata associated with the original raw file.
      • I switch to Library Module and rework the metadata within this folder; that is, I re-write the metadata title and caption making them suitable for my website.
      • When I check 'Show in Finder' I see only the jpg, not a sidecar xmp file. This suggests that the metadata is embedded in the jpg and the metadata change has brought about a jpg re-write and re-save. Is this the case?

      I wish to avoid re-saving a jpg.

      Thank you for your help -- Melody

        • 1. Re: Does changing the metadata in an exported jpg re-save and degrade the jpg?
          trshaner Adobe Community Professional & MVP

          I just tested and confirmed Save Metadata to File with JPEG is lossless (i.e. no image data recompression). You'll need to manually update the JPEG file with the new Keywords using CTRL + S.

           

          Metdata Save to JPEG Lossless Verification.jpg

          • 2. Re: Does changing the metadata in an exported jpg re-save and degrade the jpg?
            birdgeek Level 1

            Thank you for doing this research. If consistent file size means that further compression does not occur then you are correct.

            appreciatively

            Melody Lytle

            • 3. Re: Does changing the metadata in an exported jpg re-save and degrade the jpg?
              trshaner Adobe Community Professional & MVP

              birdgeek wrote:

               

              Thank you for doing this research. If consistent file size means that further compression does not occur then you are correct.

              appreciatively

              Melody Lytle

              Good point! I tested this today in PS using LR Edit in PS, Save to JPEG with Quality 6 Baseline. I then closed the file, opened the saved JPEG, and then saved again with the same Quality 6 Baseline settings. Lo and behold the file size of the 2nd resaved file was identical in size to the 1st saved JPEG file. Why? It appears PS caches the saved JPEG file and simply resaves it without recompression.

               

              To test this conclusively I closed PS after saving each JPEG, relaunched PS, reopened the last saved JPEG file, and then resaved again with a different name. The File Properties 'Size' changed for each save iteration. Sometimes the file Size went up and sometimes down very slightly, but always a different number.

               

              When using CTRL+S inside LR to update new keywords added the JPEG file Size increases progressively, as expected. If the keywords are then all removed and then metadata resaved (CTRL+S) the file Size reverts back to the original size down to the byte level. The only way you can see the file size in bytes is to look at file properties (right-click file and select Properties).

               

              Since both LR and PS use the same JPEG engine this indicates conclusively that LR Metedata Save in JPEG files does not recompress the image data.

               

              • 4. Re: Does changing the metadata in an exported jpg re-save and degrade the jpg?
                birdgeek Level 1

                Thanks mucho - changing the metadata in LR is much easier than doing so in PhotoShelter so this is helpful to know.

                Melody