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Thread: why I get jagged pictures after compression

  1. #1

    Default why I get jagged pictures after compression

    Hi,
    I seem to be getting very jagged pictures after reducing them into about 600x400, could anyone advise what could be the cause?
    my cam setting :
    - D80, fine, large

    I use MS photo editor to do auto balance to improve the contrast of the photos at times, otherwise, I do not do any editing to the photos at all.

    Thanks for your suggestions.





  2. #2

    Default Re: why I get jagged pictures after compression

    use PP that is supplied with your D80, solve your problem

  3. #3

    Default Re: why I get jagged pictures after compression

    Quote Originally Posted by CT 3833 View Post
    Hi,
    I seem to be getting very jagged pictures after reducing them into about 600x400, could anyone advise what could be the cause?
    my cam setting :
    - D80, fine, large

    I use MS photo editor to do auto balance to improve the contrast of the photos at times, otherwise, I do not do any editing to the photos at all.

    Thanks for your suggestions.
    It is expected to have these jagged once you downsize a jpg file without a proper software, even if you displaying a larger pixel jpg onto a screen that is only 600x400. They typically only works well in double sizes e.g. 1200x800 then the image would look fine. You could download one of those software that helps you 'save for web' that typically do a decent job. Photoshop Elements etc would also apply some algorithm to ensure that the scaling of pixels down to 600x400 would still be nice. Try MS editor to scale it down too, not famiiliar with it.

  4. #4

    Default Re: why I get jagged pictures after compression

    looks like the pics got overcompressed resulting in the typical jpeg square artifacts.... when downsizing you got to be careful with the compression ratio

  5. #5
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    Default Re: why I get jagged pictures after compression

    1) The jaggies or aliased edges has nothing to do with jpeg compression.

    2) improper method of scaling is the cause of these effects. using simple bilinear or bicubic will not result in jaggies. unless one is using the most simple "nearest neighbor" method.
    我吔呢班打工仔, 一生一世為錢幣做奴隸 flickr

  6. #6

    Default Re: why I get jagged pictures after compression

    Quote Originally Posted by leews2001 View Post
    1) The jaggies or aliased edges has nothing to do with jpeg compression.

    2) improper method of scaling is the cause of these effects. using simple bilinear or bicubic will not result in jaggies. unless one is using the most simple "nearest neighbor" method.
    sorry, i wasn't that clear. when you display pics that is 800x600 to a screen that is smaller e.g. 600x400 or sometimes upload to a website that would force your pics onto a smaller format, there is usually a good chance that you get really bad images, (when being 'reduced') it basically pick pixels on some algorithm or average etc. your images are showing such characteristic. Typically, if the scaling is 2X or 1/2X then your images should be fine, sometimes (depends on how the pixels are 'reduced' into the display format) it would be ok.

    thus, the surest thing to do is to resize your images (using bilinear or bicubic, if its some simple algo then that might be the cause) to the format that you are displaying. for web use 72dpi as that is the most common resolution then resize your pixels according to specification that you want to display. TVs have similar characteristics, you just have to know the resolution as well. take note that size and quality (or compression) is not mentioned, if the image looks good at 600x400 on your monitor at 1X then it would look exactly like that on any display that shows 600x400.

    hope this helps. of course, there are ALOT other reason why your your jaggies appear.

    update: i saw a screen of resizing of MS PhotoEditor, think its too basic. there should be free software online that would do a ebtter job.
    Last edited by Shuttergraphy; 19th May 2007 at 10:12 PM.

  7. #7

    Default Re: why I get jagged pictures after compression

    Big Thanks to all of you for providing me those valuable technical info. Some of the terms would take me a while to understand but ceratinly help in in a long way. I was indeed using MS Photo Editor to resize my photos before uploading, I guess that was the main cause of the problem.

  8. #8

    Default Re: why I get jagged pictures after compression

    While JPG artefacts is one reason why pictures can appear jagged, it's not apparent in your case.. This is due to a primitive interpolation (resizing) algorithm used.

    MS Photo Editor used Nearest Neighbour, which causes Aliasing thus showing the jaggedness..

    For more info, you can read http://www.cambridgeincolour.com/tut...nlargement.htm

  9. #9

    Default Re: why I get jagged pictures after compression

    Thanks Willy for providing the useful link.

  10. #10

    Default Re: why I get jagged pictures after compression

    Quote Originally Posted by leews2001 View Post
    1) The jaggies or aliased edges has nothing to do with jpeg compression.

    2) improper method of scaling is the cause of these effects. using simple bilinear or bicubic will not result in jaggies. unless one is using the most simple "nearest neighbor" method.
    pushing the compression below 50 can cause jaggies since the 8x8 clusters are averaged by too much. these 8x8 clusters are visible (i disagree with willyfoo on this) in the photos when looking at large magnification. However the interpolation method may have played a bigger role.

  11. #11
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    Default Re: why I get jagged pictures after compression

    Quote Originally Posted by Michael View Post
    pushing the compression below 50 can cause jaggies since the 8x8 clusters are averaged by too much. these 8x8 clusters are visible (i disagree with willyfoo on this) in the photos when looking at large magnification. However the interpolation method may have played a bigger role.
    those are not jaggies. those are blocking artifacts. just simply discontinuities between cosine functions at block boundaries.
    我吔呢班打工仔, 一生一世為錢幣做奴隸 flickr

  12. #12

    Default Re: why I get jagged pictures after compression

    Thanks WS. I managed to solved the problem by using Nikon PP.

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