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Thread: Resize problem - adds wrong rows (displace from up to middle)

  1. #1
    IV Amateur
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    Default Resize problem - adds wrong rows (displace from up to middle)

    Just done horizontal resize (v 4.32) nine times (838>850>800>750>700>650>700>750>800>838) to show the problem clearly.
    Click image for larger version. 

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    As you can see, it's corrupted with repeated rows! IMHO, it's seriosly.
    And if you resize horizontaly only ones it's adds one copy of middle row.
    Or something like that Click image for larger version. 

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    PS
    It work normal only with "Preserve Aspect Ratio", or for only Vertical resize.
    Last edited by Kailuz; 06.02.2012 at 04:19 PM.

  2. #2
    IV Amateur
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    Default

    So, It's dosn't fixed in v 4.33.

  3. #3
    Plugin Author
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    Default

    Maybe you should provide a test image, reproducable steps and the final image.

  4. #4
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    Default

    Hi,

    1. IrfanView is an image viewer with small editing capabilities.
    2. if you enlarge a picture there need some new data to be generated. And so it may happen that lines or rows are duplicated, depending on the used algorythm.

    Why do you use so many steps for shrinking and then enlarge to the original size?

    Regards
    Nils

  5. #5

    Default

    Open a 100x100 image, such as this one:


    Select Image -> Resize/Resample, uncheck "Preserve aspect ratio", select Size Method="Resample", Triangle filter, New size = 90x100 pixels.

    Actual result: A glitch about 75% of the way down.


    Expected result: No glitch.

  6. #6
    Professional User Mij's Avatar
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    Default

    When resampling in Irfanview you only apply the selected filter when enlarging (read what it says above the filter in the dialog). So you are not applying a triangle filter in case 2 above as you claim but whatever filter it is that Irfan has chosen for fast resampling of a reduced image.
    If instead you enlarged to 110x100 pixels and did apply the triangle filter you would see a smoother line.

    If you had a vote on "Who cares?" I doubt you would get much support!

  7. #7

    Default

    I reported the steps I used to reproduce a bug. Some of the steps may turn out to be irrelevant.

    It's true that IV normally uses an "area map" algorithm when reducing image size, but that algorithm does not exhibit glitches like this. Any anyway, the problem is with the vertical dimension, whose size is not being reduced.

  8. #8
    IV Beginner Jaff's Avatar
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    Default

    It's not a bug. There's almost no ideal way to resize an image without adding some distorsions, altering data. You might try enlarging image (resize, not resample) at 8x as example and after that resample it at needed & smaller nonporportional size. The result you expect might happen

    Name:  line1.png
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Size:  121 BytesName:  0.png
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Size:  132 BytesName:  1.png
Views: 187
Size:  482 Bytes
    1) the image (100x100)
    resize it 8x (800x800)
    2) ...the corect expected ratio (100x100 -> resize 800x800 -> resize 90x100) - only to exemplify the ratio (no glitch) and now let's use it in the right way...
    3) 100x100 -> resize 800x800 -> resample 90x100 (due to small size, all resample methods used for this sample image give the same result) No glitch! Enjoy!

    The answer and expectations are in the way you manipulate data. Filtering... chosing what data to keep and what to lose.
    Imi este indiferent ce cred ceilalti despre mine, caci oricum fiecare crede ce-i convine lui si nu ceea ce e real,
    doar ca mi-ar fi placut sa ma vada asa cum sint de fapt, nu asa cum poate le-ar placea lor sa creada. Ei au ales deja...

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  9. #9

    Default

    Irfanview's intended behavior in this situation is not documented, so no matter what it does, only someone in authority can decide whether to call it a bug or not.

    But I have to admit I'm surprised at the disagreement here. Adjusting an image's height from 100 pixels to 100 pixels is not difficult. It seems perverse to do it by deleting the first row, moving the next 75% of the image up by one row, replicating the next row, and leaving the remaining rows unchanged.

  10. #10
    IV Newbie
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    This is definitely a bug. That's why I'm still using v4.30. Those who consider this not a bug, may compare the scaling result between v4.30 and v4.32/v4.33. I think this bug is caused by "Improved Resampling (Speed; Lanczos artefacts: thanks to Marcel Lancelle)" which is added since v4.32.

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