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JPEG Artifacts

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  • JPEG Artifacts

    I was thinking today about the JPEG artifacts in my pictures and had this question: Do saving or moving my JPEG pictures add artifacts each time? For example:

    1. I take pictures with my Digital Camera (Canon A520) with the highest quality levels all the time.

    2. Then i use Micorsoft Printer and Camera Wizard to transfer the JPEG files from my SD card to my hard drive

    3. I usually open the pictures in Adobe photoshop to make any changes/edits and use crtl+s to save when im done
    a. sometimes while im editing i hit ctrl+s to save before i try something new

    4. I then usually use faststone image viewer to "loseless crop" (make a new image of the cropped section) and reduce red eyes, of course i also save after this.

    5. Ill then either transfer the pictures back to my SD card to bring to Wal-Mart, or upload online.

    6. I transfer my pics to wal-marts database and have them develop them.

    So my question is, each time i save a picture as a JPEG are more artifacts added? What about when transfering pictures? Does wal-mart lower the compression or anything when i transfer the pictures to them?

    Thanks for any help! I'd Also appreciate any ideas on how to limit the number of saves i make when editing.

  • #2
    Hi Justone and welcome to RP!
    The JPG format is a "lossy" compression format. Transfering files from Camera to computer or duplicating the files on a computer does not alter them. However, every time you save the file after opening, even if you have done nothing to it, degrades the quality of the image further. How much and how quickly depends on the compression factor, which in PS goes from 1 to 12 with 12 being highest quality and 1 being ... well giant ice cubes.
    You should always keep you original file and work on a duplicate of it. If you absolutely must save the same file and can not Save As wit a new file name, then you should use the highest number 12 (lowest compression). Better still, save in a format which is lossless like PSD (native Photoshop) or a Tiff with compression set to Lossless.
    Regards, Murray


    • #3
      Saving at the highest setting won't degrade too quickly, although it is always better to save on lossless formats.

      However, if you are saving as JPG, this is the killer....
      Originally posted by justone
      4. I then usually use faststone image viewer to "loseless crop" (make a new image of the cropped section)
      JPG divides your image in 8 x 8 blocks and codes each block individually. Which explains the strange grid pattern you sometimes see.
      If you do not resize, and if you maintain the top left corner of you image the lines will always fall in the same place.
      However any resizing, cropping, cutting operation will surely change the where the 8 x 8 blocks fall and the degradation willl mount up quickly.


      • #4
        My work flow is to download images from the camera to the hard drive then run a batch action (a dropplet) in PhotoShop to save the images as 300 DPI TIFF files to a new folder.

        I also run another batch action and save low res JPEGs which I then add to iPhoto (smaller file sizes) for future viewing, sorting, labeling, rating etc. If I need to locate a photo I can get the date from the iPhoto info and pull the corresponding CD.

        I keep a folder on my hard drive called "Burn to CD" that I use to store photo folders (folders have the date as the name) until I have enough to fill a CD then archive all the TIFFs to CD. I label the CD with the inclusive dates of the enclosed folders.


        • #5
          ok thanks a lot. That really helps. As far as cropping the pictures goes, that makes since... so is there anyway to really crop a picture from a Digi cam that is saved as a JPEG, wihtout creating extra artifacts or do you just have to deal with it? (my camera cant take RAW)


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