Quick Answer
A document scanner turns photos of papers into clean, straight pages and bundles them into a single PDF. Point your camera at a page (or upload images), let auto-crop find the edges, drag the four corners to correct it, and pick an enhance mode — original color, grayscale, or black and white. This free scanner does the perspective correction, warping, and PDF assembly entirely in your browser, so your camera stream and documents never leave your device, and no account is required.
How It Works
Add pages: open the camera and capture each page at full resolution, drop image files onto the upload zone, or load the synthetic sample
Check the crop: auto-crop proposes corners from the page edges — drag the four handles (arrow keys nudge the selected corner) until the quad hugs the page
Pick an enhance mode: original color, grayscale with 2nd–98th percentile contrast stretch, or Bradley adaptive black & white for text
Apply crop & enhance: the homography warp flattens the page in chunks with a live progress percentage
Export: reorder or delete pages in the strip, download the multi-page scan.pdf, or save any single page as a PNG — everything stays on your device
Key Facts
- Capture from the camera at full sensor resolution, or upload multiple images at once
- Four draggable crop corners with pointer and keyboard control, working at any zoom level
- Auto-crop proposes edges from Sobel gradient ridges — and says so honestly when it can’t
- Perspective correction via a hand-rolled 3×3 homography solved with Gaussian elimination, then per-pixel bilinear inverse mapping (no OpenCV)
- Enhance modes: original color, grayscale with 2nd–98th percentile contrast stretch, or Bradley adaptive black & white
- Warp runs in chunks with progress, so 12-megapixel photos never freeze the page
- Reorder pages, delete with confirmation, and re-edit any page — corners and mode are remembered
- Export one multi-page PDF (Letter-sized, custom-sized when a page’s aspect differs by more than 25%) or download any page as PNG
- Everything runs locally in this tab — camera and documents never leave your device
Frequently Asked Questions
How does the perspective correction work?
Your four crop corners and the target rectangle define a 3×3 homography — the standard projective transform for flattening a photographed page. The scanner solves it as an 8-equation linear system with Gaussian elimination (with partial pivoting), then walks every output pixel backward through that transform and samples the source photo with its own bilinear interpolation. There is no OpenCV and no canvas-transform shortcut; the output size comes from the longest pair of opposite quad edges, so the page keeps its true aspect ratio.
How does black & white mode decide what is ink?
It uses Bradley adaptive thresholding: for each pixel it compares brightness against the mean of a surrounding window (about 1/16 of the page width, computed instantly with an integral image) and keeps the pixel black when it falls below 0.82 of that local mean. The local window is what preserves faint pen strokes and handles uneven lighting, where a single global threshold would wash out part of the page.
Is this document scanner free?
Yes — free, unlimited pages, no watermarks, and no account. Commercial scanner apps gate similar features: CamScanner’s free tier brands exports and pushes a subscription, and Adobe Scan requires signing in with an Adobe account and routing documents through Adobe’s cloud. This tool has no paid tier because it has no servers to pay for.
Is it private? Where do my documents go?
Nowhere. The camera stream, the photos, the cropping math, and the PDF assembly all run locally in this tab — open your browser’s network inspector and you will see zero uploads. The camera stops the moment you close it or leave the page. That is also why it keeps working offline once the page has loaded.
What can I scan, and what do I get out?
Any image your browser can decode — camera captures, JPG or PNG photos of receipts, letters, forms, whiteboards. Each image becomes one page you can re-crop and reorder. Export is a single multi-page PDF (scan.pdf) with Letter-sized pages; a page whose aspect ratio drifts more than 25% from Letter, like a long receipt, gets its own correctly-proportioned PDF page. Each page can also be downloaded on its own as a PNG.
Why does auto-crop sometimes ask me to adjust the corners?
Auto-crop looks for the four strongest Sobel gradient ridges near each border — the edges of a page against a darker surface. It only claims success when those ridges clearly stand out from the background and form a sane convex quad. On a busy desk, a curved page, or a document photographed edge-to-edge, it says so and leaves the default corners for you to drag, instead of confidently cropping the wrong region.