To straighten a crooked photo, rotate it by the opposite of its tilt using a custom angle, then crop the empty corners. A horizon that slopes down to the right needs a counter-clockwise turn (a negative angle). One that slopes up to the right needs a clockwise turn (a positive angle).
This guide shows how to measure the tilt, which angle to enter, and how much to trim afterwards.
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Key takeaways
- Positive custom angles turn the picture clockwise; negative angles turn it counter-clockwise.
- Small angles of one to five degrees fix most crooked horizons and scans.
- After rotating, the corners are empty, so crop them away.
- Trim roughly two percent from each side for every degree of tilt.
Steps shown in the video
- Click Choose Images and select the photos to rotate
- Each file is listed with a preview and its size
- Choose the angle, here 90° clockwise
- Click Rotate images
- Download your rotated images
Step 1: Measure the tilt
Find a line that should be perfectly horizontal or vertical: the horizon, a table edge, a building or the top line of text on a scan. Compare it with the top edge of the image.
- Sloping down to the right: the picture is tilted clockwise, so enter a negative angle.
- Sloping up to the right: the picture is tilted counter-clockwise, so enter a positive angle.
- How many degrees? One degree is about 1.7 pixels of drop for every 100 pixels of width. A line that falls 35 pixels over 1000 pixels is tilted by 2 degrees.
Step 2: Rotate
- 1
Open Rotate Image and add the photo.
- 2
Choose Custom angle and type the correction, for example -2 for a horizon that slopes down to the right by about two degrees.
- 3
Rotate, download and compare the horizon with the edge of the picture. Adjust by half a degree and repeat if needed.
Step 3: Crop the empty corners
A custom rotation enlarges the canvas, and the corners fill with transparency (PNG and WebP) or white (JPG). To remove them, open the rotated image in Crop Image, choose Free (margins only) and enter the same percentage in all four trim fields. These starting values suit a 4:3 photo:
| Tilt corrected | Trim on each side | What remains |
|---|---|---|
| 1° | 2 to 3 percent | About 95 percent of the area |
| 2° | 4 to 5 percent | About 90 percent of the area |
| 3° | 5 to 7 percent | About 85 percent of the area |
| 5° | 8 to 10 percent | About 75 percent of the area |
These are guides, since the exact figure depends on the shape of the picture. Check the preview and add a point or two if a sliver of corner is still visible.
Straightening scans and photos of documents
A page scanned slightly crooked looks sloppy and can confuse text recognition. Straighten it with the same method, using a small negative or positive angle until the lines of text run parallel to the top edge. A white-filled corner on a white page is invisible, so JPG scans often need no cropping at all. When the page is ready, Image to Text reads it more accurately, and PNG to PDF can assemble the pages.
Does a tiny rotation hurt quality?
Angles that are not multiples of 90 degrees require resampling, which means that pixels are blended slightly. At one to three degrees the effect is invisible at normal viewing sizes. Quarter and half turns move pixels exactly and cost nothing. For the basics of quarter turns, see how to rotate an image online.
When you want a creative tilt
Custom angles also work for deliberate effects, like a slightly rotated product photo or a diagonal banner. PNG keeps the corners transparent, so the result can sit on any background. If you want a mirror effect rather than a tilt, look at Flip Image.
Straightening photos: FAQ
How do I straighten a crooked photo?
Use a small custom rotation in the opposite direction of the tilt, then crop away the empty corners.
Which angle should I enter?
Enter a negative number if the horizon slopes down to the right, and a positive number if it slopes up to the right.
How much should I trim afterwards?
Roughly two percent from each side for each degree of correction, for a 4:3 photo.
Why are the corners white?
JPG cannot store transparency, so the new corners are filled with white. PNG and WebP keep them transparent.
Can I use decimals such as 1.5 degrees?
Yes. Type the decimal straight into the custom angle field. Its arrows step by whole degrees, but typed values such as 1.5 or -0.5 are used as entered.
Does straightening reduce quality?
A small rotation slightly blends pixels, which is invisible at normal sizes.
Can I straighten a scanned PDF?
Convert the page to an image, straighten it here, and turn it back into a PDF.
Will the aspect ratio change?
The canvas grows after rotation. Cropping to a ratio such as 3:2 brings back a standard shape.
Level it, then trim
Measure the tilt, rotate by the opposite angle and crop away the corners. Two small steps give a clean, level picture.
