Tutorial: Rotating Skewed Images Accurately

Darren · 4th July 2003

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 · 4th July 2003

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 · 4th July 2003

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 · 4th July 2003

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 · 4th July 2003

Tutorial

This link will be useful.

Fella · 4th July 2003

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!

4th July 2003

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

Darren · 4th July 2003

Quote:

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

Fella · 4th July 2003

Quote:

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!

Jed · 4th July 2003

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

Java_Guru · 4th July 2003

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

4th July 2003	#1
Darren ClubSNAP Admin Join Date: Jan 2002 Location: ClubSNAP HQ Posts: 7,473	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:- __________________ Tweet?

4th July 2003	#2
Darren ClubSNAP Admin Join Date: Jan 2002 Location: ClubSNAP HQ Posts: 7,473	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:- __________________ Tweet?

4th July 2003	#3
Darren ClubSNAP Admin Join Date: Jan 2002 Location: ClubSNAP HQ Posts: 7,473	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 - __________________ Tweet?

4th July 2003	#7
Allen Guests Posts: n/a	Perspective Correction Turn on rulers, Ctrl-' and place a ruler along all vertical lines and then Ctrl-A, Ctrl-T and drag corner nodes.

4th July 2003	#4
StreetShooter Moderator Join Date: Jan 2002 Location: Katong Posts: 4,702	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.

4th July 2003	#5
blizzy Member Join Date: May 2002 Location: Bedok South Posts: 616	Tutorial This link will be useful.

4th July 2003	#6
Fella Member Join Date: Dec 2002 Posts: 704	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!

4th July 2003	#10
Jed Senior Member Join Date: Jan 2002 Location: UK Posts: 3,082	Actually, this way works but I don't think it's the most efficient. There is another way

4th July 2003	#11
Java_Guru Member Join Date: Feb 2002 Posts: 785	u can actually ROTATE and CROP at the same time. But u need a steady hand/optical mouse and keyboard to do well.