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rejection again due to compression artefacts

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  • rejection again due to compression artefacts

    Hi guys,

    I am going to bother you again with questions.

    I had this pica rejected:

    I used the equalize function to see where the artefacts are. I can only see it in the sky, is that right? I can read the KLM logos and the registration clearly, so it probably won't be there.

    Didn't I do right to first crop/resize, then sharpen etc.?
    Or should I photoshop the photo in its original format and then resize/crop in phases? Because if I resize from the original size to 1024x768 I always get those compression artefacts rejections.

    Someone on this forum told me to save in tiff format.
    Should I in that case photoshop the photo, then resize/crop to 1024 in tiff format and then convert this 1024x768 file to jpg?

  • #2
    What image quality do you you shoot at ( i.e. RAW, jpg fine etc. ) ?
    ...and the sky is very definitely showing compression artefacts.
    If it 'ain't broken........ Don't try to mend it !


    • #3
      I shoot in jpg.
      Since I am a beginner I think jpg is good for me. I saw you, Brian, getting "reprimanded" for advising another beginner to shoot in RAW

      Yes, you are right ... the sky looks crappy in the picture.

      Is there special resize software that limits compression artefacts? Or is the resize function in Adobe PS all right?


      • #4
        The reason I use RAW is that even jpg fine has a compression ratio of 1:4 whereas RAW is 0 compression.

        Using RAW does mean that you need a pretty good piece of processing software from the adobe CS range. I believe that Photoshop 7 has a RAW plug in available but I don't think there is one for PS Elements. I certainly found a plug-in for CS2 and CS3 recognises RAW anyway withouta plug-in download being needed.

        I've never used TIFF format so what follows may need correcting by someone, and you should certainly get other opinions before accepting my words of dubious wisdom.

        What you could possibly do is open your jpg, convert to TIFF format and bring your crop down in stages, making your last save as a jpg. I really can't comment though on at which point you would commence the processing required.
        If it 'ain't broken........ Don't try to mend it !


        • #5
          PS elements indeed recognizes RAW.
          I have first saved in TIFF, then resized in stages in TIFF. When having reached 1024 I saved the TIFF to jpg. Results are way better. I think I'll follow this procedure for a while.


          • #6
            I normally crop to 1200 straight off. I think I'll have to try this staged cropping.
            If it 'ain't broken........ Don't try to mend it !


            • #7
              Well, if your pictures are good the way you crop them, there is no reason for you to change your process, is there?


              • #8

                The compression artifacts seen in your example above are coming from the Saving process, not the resize process. The JPEG compression that is being applied in either a) the camera, or b) you editing processes before upload, are creating the artifacts.

                If you are doing a multistage size reduction, do you save after each resize? You shouldn't have to do that. If your shooting JPEG in camera, open the pic, edit it, then Save it in JPEG (best quality) this should avoid any artifacts. Multi saving the saem pic over and over again causes the artifacts.

                Explanation: When JPEG saves at a certain quality it tries to use lossless compression as much as possible, however at some point the compression is going to have to start to throw some parts of your picture away to make the file size. Initially these bits that are thrown away are non-visible parts but if you repeatedly save with JPEG compression, eventually it starts to throw away visible bits that make up the picture. The bits that it throws away are usually in the detail of the picture (more information is needed to produce the sharp edges), hence the picture starts to look soft when too much compression is applied. When you remove too much info, the edges cant be well defined, and start to look noisy, or artifacts. In your example picture above way too much info has been removed and even some of lower detail info has gone, so this causes blocks in the sky (called macroblocks). So either the pic has undergone to many resaves with JPEG, or the compression was to high on a single save.

                Hope this helps


                • #9
                  Hi Billsville,

                  Thanks for your post. I never use multistage size reduction. I edit the pic, then after that process I save to jpg in best qualitiy (12 in Photoshop elements). But I'll play with it and I am sure one day I'll master the skills



                  • #10
                    ...and that, Stephen, is the best plain English description of compression that I've seen.
                    If it 'ain't broken........ Don't try to mend it !


                    • #11
                      And thats just the abridged version


                      • #12
                        Originally posted by Hinkelbein
                        I shoot in jpg.
                        Most cameraas have also different quality settings for jpeg.
                        Which one are U using?
                        If you are saving with the highest quality setting in Photoshop (or whatever your editing program is) then the source of the artifacts might be in the camera.
                        What are the dimensions of your files when you downlaod them from your camera? (pixels and size in bytes)


                        • #13
                          3888 x 2592
                          Size: 3,34 MB

                          That is the best quality options in the camera.