Straighten a Crooked Photo and Fix Skewed Perspective with Paint Shop Pro

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Straightening a Crooked Photo

Crooked Photo
Save the practice image.

Corel Paint Shop Pro X has a couple useful new tools for straightening a crooked photo and fixing skewed perspective. Anytime you have a crooked photo, keep in mind that you will have to lose something from the edges of the photo. The sides of the image will have to be cropped to make up for the slanting of the photo from rotation. Since you always have to crop a photo when you rotate, Paint Shop Pro will do the rotate and crop in one step, when you use the specialized straighten and perspective correction tools.

Right click on the image above and save it to your computer if you'd like to follow along. Then open the image in Paint Shop Pro and continue to the next page.

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Paint Shop Pro Straighten Tool

Paint Shop Pro Straighten Tool

Select the Straighten tool in the tools toolbar. When you do, you will see a line across your image, and the tool options bar will appear for the straighten tool. In the options bar, make sure that mode is set to 'Auto' and that crop image is checked.

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Setting the Horizon Line for Straightening

Setting the Horizon Line for Straightening

Then go to your image and move the two end points of the line, so that the line corresponds with the horizon line in the image. In this beach scene, we are using the true horizon line, but in some photos you might not have a true horizon line to work with. In those cases, you can use any line that should be horizontal - it may be a roofline, sidewalk, fence, or something else.

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Applying the Straightening

The Straightened Image

Once you have the line positioned, click on the green checkbox, or simply double click anywhere in the image to rotate and crop in one step.

If you'd like to see the difference without having the Crop Image box checked, press the undo button and try it again with crop image unchecked. The image will be rotated, and the extra space one each side is filled with the background color.

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Correcting Perspective Distortion

Perspective distortion often occurs in pictures of tall buildings
Save the practice image.

Next let's work with an image where the perspective is distorted. This often occurs with pictures of tall buildings, such as the one shown here. Right click on the image above and save it to your computer if you'd like to follow along. Then open the image in Paint Shop Pro and continue to the next page.

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Paint Shop Pro Perspective Correction Tool

Perspective Correction Tool

Select the Perspective Correction tool in the tools toolbar. When you do, you will see a rectangle appear over your image, and the options bar will show you all the controls for the perspective correction tool. Don't freak out when you see all those numbers in the options bar! In fact, you needed worry about them at all. Just make sure that the 'Crop Image' box is checked.

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Setting the Grid for Perspective Correction

Setting the Grid for Perspective Correction

If you like, you can enable grid lines. For this image I have entered 3 in the grid lines box. As you can see it adds grid lines to the rectangle which can be helpful in getting the control handles aligned with the image we are going to straighten.

Then go to your image and move the four corner points of the control rectangle so that it aligns with the building in your image. Make sure the top and bottom lines of the rectangle are aligned with part of the photo that should be horizontal, and make sure the left and right lines of your rectangle align with the sides of the building.

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Applying the Perspective Correction

The corrected image.
The corrected image... looks a little odd, doesn't it?.

Once you have the four edges of the rectangle positioned, click on the green checkbox, or simply double click in the image to rotate and crop in one step.

But does the corrected photo look a little unnatural to you? Continue on and I'll explain why...

If you'd like to see the difference without having the Crop Image box checked, press the undo button and try it again with crop image unchecked. The image will be rotated, and the extra space one each side is filled with the background color.

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Perspective Correction Makes the Photo Look Unnatural

Leave a little distortion to make the photo look more natural.

You may find that the image looks a little odd after correcting it. The building will often appear distorted in the opposite way, even though the walls are aligned vertically. That's because your brain expects to see some perspective distortion when looking up at a tall building. Graphics guru and author Dave Huss pointed this out to me, and offered this tip:

"I always leave a little of the original distortion to make the image appear natural to the viewer."

You can see how to do this in the screen shot above. You only need to compensate a tiny bit for the corrected photo to appear much more natural.

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Perspective Correction, Take Two

Perspective correction now looks more natural.

As you can see from the guidelines I've placed in the photo, this second attempt at correction is slightly "wrong" but it looks more "right" to the eye than the first attempt at perspective correction.