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  • jpeg compression

    can someone help me out on jpeg compression what is it how can i stop it i need as much advice as possible any advice would be great thanks.

  • #2
    jpeg is a compressed image format, as smaller the file size is, as more compressed is the image file. If you apply too much compression to the images you'll lose quality and there will be squares visible in the image. If you can't see it in the image clearly, raise the the contrast, and you'll see them. Compare to the examples listed here: http://en.wikipedia.org/wiki/JPEG#Photographs

    Save your images after editing in the highest quality, in Photoshop it's Quality = 12, other image editing programs may have there a value in %, here use the value 100. You should avoid to edit jpegs twice, so once edited and resized and saved, don't edit them again, this could cause thoses compression artefacts, too.

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    • #3
      Iron, I will try and take screenshots when I edit a photo and then send it to you via email. At least give me a chance to do stuff and then email you back instead of posting in the forums. I am trying my best to give you a helping hand.

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      • #4
        Another thing to remember is that every time you open a JPEG photo and resave it in JPEG you are degrading the photo that little bit more.

        JPEG is described as a lossy form of compression, which basically means it has to throw parts of the photo away to achieve the file size. The compression algorithm tries to do it by removing the less visible information, but if you specify a smaller file size it has no choice but to start to remove the visible components.

        As you open and close the picture, where the information has been removed before now looks different to the JPEG compressor, so it now has to throw different parts of the information away. If you keep on this cycle you can see that your picture can degrade easily with all the information being removed.

        An easy way to see this is to get a clean picture, and just open and re-save it as JPEG file. Depending on the quality level you have set the degradation will be noticeable within 3-5 saves.

        So if your shooting JPEG in your camera, always shoot at the highest quality. If you want to edit in multiple steps, try saving in a non-destructive format like TIFF and TGA (who use lossless compression), then save to JPEG as the last step before uploading.

        Hope this helps.
        Steve Brown

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