Perspective Correction Online
Drag the four corners onto the thing that should be rectangular. Get it straight, at full resolution, without uploading anything.
How to fix perspective in a photo
Point-and-shoot photos of buildings lean backwards, whiteboards photographed from a seat are trapezoids, paintings snapped in a gallery are never square. All of these are the same problem: a flat rectangle seen from an angle. Give the tool the four corners of that rectangle and it computes the exact transform that puts it back.
Open your photo, then drag TL, TR, BR and BL onto the corners. Zoom the browser if the corners are small. The result preview updates as you drag; when it looks right, download at full resolution.
Choosing the output shape
Auto estimates the rectangle's real proportions from how the four corners are arranged in perspective. For documents you know the size of, set it directly: A4 or Letter for pages, 16:9 for screens and TVs, square for album covers and tiles. A wrong ratio produces a result that is straight but stretched, which is easy to spot on text.
Where the pixels come from
Straightening stretches the far side of the object, so the part that was small in the photo is enlarged and loses sharpness. Shoot as square-on as you can and use the correction to finish the job rather than to rescue a photo taken from a sharp angle. For scanned documents, add a light sharpen afterwards.
The same thing inside your app
Photoshop: the Perspective Crop tool, or Edit → Perspective Warp. Affinity Photo: the Perspective tool in Source/Destination mode (lesson). Lightroom: Transform → Guided. GIMP: the Perspective tool in Corrective mode. This page does it without installing anything, and at full resolution.
Related
If you are correcting a photo to draw over it, the 3-point grid can match the camera angle first, and the perspective warp tool does the reverse job: putting a flat image back into a photo.
Questions
How does perspective correction work?
Four corner correspondences define a projective transform (a homography) exactly. The tool computes it from where you put the handles and where a rectangle of the chosen shape would be, then resamples every output pixel from the photo with bilinear filtering. It is the same mathematics Photoshop's Perspective Crop and Lightroom's Guided Upright use.
Is my photo uploaded anywhere?
No. The image is read into your browser's memory and processed there. Nothing is sent to a server; the site has no upload endpoint.
Why does the result look stretched?
Auto estimates the real proportions from the shape of the quad, which works well for moderate angles. For extreme angles or objects with known proportions, pick the ratio explicitly (A4, 16:9, square).
Can it straighten a whole building, not just one face?
It straightens one plane at a time. Put the handles on the corners of the main façade; the rest of the photo is transformed consistently. For two faces at once, use the 3-point grid to plan and Photoshop's Perspective Warp with two planes.
What is the maximum image size?
There is no fixed limit; large phone photos (12–48 MP) work but take a few seconds to render at export. The output width is capped at 4,000 px.