Tutorial: Rotating Skewed Images Accurately

[Darren]

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:-

 

[Darren]

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:-

 

[Darren]

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 -

 

[StreetShooter]

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.

 

[blizzy]

Tutorial

This link will be useful.

 

[Fella]

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... :dunno:

Thank you very much!

 

[Allen]

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

 

[Darren]

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 ... :cry:

Guide to Resizing and Cropping by Darren

shameless self-promotion ;p

 

[Fella]

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

Guide to Resizing and Cropping by Darren

shameless self-promotion ;p

My apologies!! :embrass:
Anyway, it's a life-saver! :thumbsup:

 

[Jed]

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

 

[Java_Guru]

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