Grayscale Image Converter

This converter turns a colour image into shades of grey — or into pure black and white — directly in your browser. It is for making a photo black and white, turning a scan or a line drawing into crisp 1-bit black and white for printing, greying out a picture for a document or a mock-up, or prepping an image where only brightness matters. The file is never uploaded to a server.

You choose how the three colour channels collapse into one grey value. Perceptual (recommended) weights green most and blue least, which is how the eye judges brightness — a red and a green of the same "brightness" do not look equally bright, and this matches the familiar black-and-white photo look. Average adds red, green and blue and divides by three: simple and neutral, and it treats every colour the same. Lightness takes halfway between the brightest and darkest channel; it keeps strongly coloured areas from going muddy, which suits logos and flat graphics.

For pure black and white, tick the threshold and set the cut (1–254). Every pixel at or above the cut becomes white and every pixel below it becomes black, so the result is a strict two-colour, 1-bit image. That is the right mode for scanned text, signatures, stamps and line art, where grey shading is unwanted; it is the wrong mode for photographs, where it discards most of the detail and leaves heavy blotches. The threshold slid from one end to the other is the only control: raise it to keep more dark areas, lower it to keep more light ones.

Transparency is preserved. A PNG with a transparent background stays transparent no matter which mode you pick — only the visible colour is greyed. Nothing else about the picture changes: the pixel dimensions are untouched, and the output is saved in the same format where the browser can (PNG, JPG, WebP). GIF, BMP and AVIF cannot be re-encoded by a browser canvas, so those are saved as PNG, which is lossless; an animated file keeps only its first frame.

How it works: your browser decodes the image (a phone photo is turned upright using its EXIF orientation), draws it onto a canvas at full size, and this tool rewrites the red, green and blue values of every pixel in JavaScript on the raw pixel data. The canvas is then re-encoded and offered as a download. Because the picture is redrawn on a canvas, EXIF metadata — camera, date and GPS location — is not copied into the result, which is a privacy gain in itself.

Limits: up to 50 images at a time, 50 MB each, and about 100 megapixels (16,384 px per side). iPhones and iPads allow a canvas of only about 16.7 megapixels, so a very large photo may fail there with a message saying so. Your images stay on your device: the Network tab in your browser's developer tools shows no request carrying them.

1. The file's size is checked (50 MB) before it is read, and its first bytes confirm it is PNG, JPG, WebP, GIF, BMP or AVIF; the browser decodes it upright. 2. The image is drawn onto a canvas at full size and its RGBA pixels are read. 3. Each pixel's grey value is computed from its red, green and blue channels: • Perceptual: 0.2126 R + 0.7152 G + 0.0722 B (Rec. 709 luma coefficients), rounded. • Average: (R + G + B) ÷ 3, rounded. • Lightness: (max(R, G, B) + min(R, G, B)) ÷ 2, rounded. 4. If a threshold is set, the grey value becomes 255 when it is at or above the cut and 0 when it is below it. 5. Red, green and blue are all set to that value; the alpha channel is left exactly as it was. 6. The pixels are written back, the canvas is encoded, and the file is named like photo-grayscale.jpg or scan-black-and-white.png.