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I shot an image of a street reflected in a large fisheye mirror. The telephone lines in the background and everything else was fine. I gave it a very slight crop (less than ten percent) and suddenly the telephone lines became dotted lines like morse code. I did preserve aspect ratio while cropping. What can I do to fix this and why did it happen?

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  • \$\begingroup\$ What software are you using? How high of resolution does your original have? Does tge effect persist if you change the zoom level? What if you view with different software? Did you rotate at all while cropping? \$\endgroup\$
    – mattdm
    Commented Apr 12, 2016 at 11:58
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    \$\begingroup\$ And, can you post your image? \$\endgroup\$
    – mattdm
    Commented Apr 12, 2016 at 11:59
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    \$\begingroup\$ Did you CROP it (which means removing outer parts of an image) or did you RESIZE it (which means scaling image in terms of size in pixels)? \$\endgroup\$
    – Zenit
    Commented Apr 12, 2016 at 13:03

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A. There is a good chance that the issue is only in your display software (meaning not in the picture). If the number of pixels in the display is different of the number of pixels in the picture, the software needs to make it fit somehow. Depending on the level of sophistication in the code, it simple skips every Nth pixel row, which results in potentially the only pixel row with the telephone line being not displayed.

B. (Less probable - the result would look different) If you save your picture as JPG, you need to understand that JPG is not generally lossless; most save dialogs give you the option to lose between 0% and 99%. The default is mostly 20% loss, but it depends of course on your software and settings. So if you edit anything and then save, you lose 20%, next open and save another 20%, etc.

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  • \$\begingroup\$ I agree with A, but B isn't a good description of how JPEG compression level works. (Also, probably not relevant here.) \$\endgroup\$
    – mattdm
    Commented Apr 12, 2016 at 12:47
  • \$\begingroup\$ @mattdm, i see what you mean. the errors introduced by JPG loss would probably look different from what he experienced. It wouldn't be dotted lines, but more a general smearing and fuzziness. \$\endgroup\$
    – Aganju
    Commented Apr 12, 2016 at 12:55
  • \$\begingroup\$ I am using Corel PhotoPaintX7 and this was shot in a camera that only takes JPEG (it was pouring rain and I had a waterproof 10MP Panasonic). Yes, the image problem comes and goes at different zoom levels. Resolution was reasonably high, 5MB image. I have not viewed it with different software. And the reason I am not currently using Adobe is (1) Corel does lots of stuff very well and intuitively (2) everyone who has put down Corel to me has never used it (3) Adobe is a nightmare to learn. \$\endgroup\$
    – M Bennett
    Commented Apr 18, 2016 at 17:03

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