Online Document Scanner

Turn a phone photo of a page, receipt or form into a clean, flat scan. The page edges are found automatically, the perspective is straightened, shadows are removed and you can save every page as one PDF. Nothing is uploaded.

Last updated: October 24, 2026

How to use the Online Document Scanner

1. Add photos of your pages: drop them on the box, press Choose photos or Take photo on a phone. A sample page is loaded so you can try it.
2. Check the corners: the page edges are detected automatically. Drag any corner onto the paper corner if needed; the loupe shows a zoomed view while you drag.
3. Pick a scan mode: Auto color whitens the paper and keeps colors, Grayscale is neutral, B&W gives crisp black text. Use Clean-up strength or Threshold to fine-tune.
4. Add more pages and use the arrows, rotate and delete buttons in the page strip to put them in order.
5. Download PDF to save all pages in one file, or Download page to save the current page as an image.

How the scanner turns a photo into a flat page

1. Edge detection. The photo is reduced to about 320 pixels, blurred and split into bright and dark areas with Otsu's threshold. The largest connected bright region is taken as the paper, and the four points of its convex hull that enclose the biggest area become the corners.
2. Perspective correction. The four corners define a projective transform (a 3 × 3 homography with 8 unknowns, solved from the 4 corner pairs). Every pixel of the flat output page is mapped back into the photo and sampled with bilinear interpolation. The output width is the longer of the top and bottom edges, the height the longer of the left and right edges.
3. Lighting clean-up. The page is divided into small blocks and the brightest value in each block is taken as the local paper color. That background map is smoothed and every pixel is divided by it, which removes shadows, gradients and yellowish light and makes the paper white. A levels curve then deepens the ink.
4. Black & white. After the lighting correction each pixel is compared with the Threshold: brighter becomes white, darker becomes black. Because the threshold is applied after removing shadows, it works across the whole page even in uneven light.

Scan mode guide

Tips for better phone scans

• Put the page on a dark table or a dark sheet so the edges stand out.
• Use daylight or two light sources to avoid one-sided shadows; avoid the flash, which causes a bright glare spot.
• Fill most of the frame with the page while keeping all four corners visible.
• Hold the phone steady and tap to focus on the text; a sharp photo matters more than a straight angle.
• For multi-page documents, photograph all pages first, then drop them in at once and reorder in the page strip.

Frequently asked questions

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