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Thread: Tutorial: Rotating Skewed Images Accurately

  1. #1
    ClubSNAP Admin Darren's Avatar
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    Lightbulb Tutorial: Rotating Skewed Images Accurately

    This tutorial is for the benefit of members who routinely ask how to correct skewed images. Enjoy!

    Acknowledgement: The image used here was taken from ClubSNAP member hong from this thread for lack of any suitable image in my library. If hong has any objection, I will remove this image and try to get another one.

    This is the original image as posted:-

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    ClubSNAP Admin Darren's Avatar
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    We will use the Measure tool to accurately determine the angle for correction. The Measure tool is found here:-


    Using the Measure tool, we then measure a known good horizontal or vertical line in the image. In this example, I measured the vertical side of the HDB block as shown:-


    Next we use the Arbitrary Rotate menu command to do the actual rotation. The menu can be found here:-


    which will bring up this dialog box with the angle and direction of rotation already entered, and all you have to do is to hit ENTER:-

  3. #3
    ClubSNAP Admin Darren's Avatar
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    The result of the rotation will be a canvas which shows an image with corrected verticals, but with white spaces where the canvas has been "expanded" in the rotation process:-


    We then do a crop to get the final image as shown here -

  4. #4

    Default

    To confirm that the image is indeed correctly aligned, I would suggest turning on the grid ie View > Show Grid.

    This is especially so if you want to correct converging or diverging verticals as well, using Distort.

  5. #5

    Default

    Tutorial

    This link will be useful.

  6. #6

    Default

    This is great!
    Thus far, I've always been using "agar-ation"!
    Very much thanks!

    How about a tutorial on correcting converging or diverging verticals? I'm quite sure many users (myself inclusive) will benefit from it.

    Have another question which I hope someone can help.
    After doing a rotation, let's say I wanna crop the picture to a particular size of exactly x times y pixels, how do I actually go about doing it? At the moment, what I do is "agar-ation" again, just select, resize down and hope for the best...

    Thank you very much!

  7. #7
    Allen
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    Default Perspective Correction

    Turn on rulers, Ctrl-' and place a ruler along all vertical lines and then Ctrl-A, Ctrl-T and drag corner nodes.

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    ClubSNAP Admin Darren's Avatar
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    Originally posted by Fella
    Have another question which I hope someone can help.
    After doing a rotation, let's say I wanna crop the picture to a particular size of exactly x times y pixels, how do I actually go about doing it? At the moment, what I do is "agar-ation" again, just select, resize down and hope for the best...
    This one already done ... *sigh* we all die-die write review no one refer to ... very, very sad ...

    Guide to Resizing and Cropping by Darren

    shameless self-promotion

  9. #9

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    Originally posted by Darren
    This one already done ... *sigh* we all die-die write review no one refer to ... very, very sad ...

    Guide to Resizing and Cropping by Darren

    shameless self-promotion
    My apologies!!
    Anyway, it's a life-saver!

  10. #10
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    Actually, this way works but I don't think it's the most efficient. There is another way

  11. #11

    Default

    u can actually ROTATE and CROP at the same time. But u need a steady hand/optical mouse and keyboard to do well.

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