モノクロ変換

What this tool produces

Grayscale Image converts color photos to monochrome locally in your browser. The output keeps original resolution, supports JPG, PNG, and WebP export, and lets you fine-tune contrast and brightness so the final image is print-ready, accessible, or stylised — without sending the source anywhere.

Picking a grayscale method

Lightness averages the brightest and darkest channel, preserving midtone detail. Luminosity weights the green channel highest, matching human perception, ideal for portraits and photographs. Average mixes channels equally — flat, fast, and neutral for graphics or charts.

Fine-tuning the result

Use Contrast to push midtones toward pure black and white. Use Brightness to lift or darken the overall image. Saturation defaults to fully desaturated; raise it to keep partial color for split-tone effects. Toggle Auto-enhance contrast to stretch the histogram on low-contrast scans.

Privacy and limits

Files stay on your device. Maximum input size is 20 MB. For related workflows see the Blur Background tool, the Flip Image mirror, or the Image Converter for format changes.

What does the Grayscale Image tool do?

It converts color photos and graphics to black-and-white directly in your browser. Choose a grayscale formula, fine-tune contrast, brightness, and saturation, then export as JPG, PNG, or WebP.

Which method should I pick?

Luminosity is closest to how the human eye perceives brightness — pick it for portraits and photographs. Lightness keeps more midtone detail and works well for landscapes. Average gives a flat, neutral conversion useful for icons and flat illustrations.

Why does the saturation slider stay at -100 by default?

Full desaturation removes color while keeping the original luminance — this is a true grayscale. Slide it back toward 0 to keep partial color, useful for split-tone or sepia-style edits.

What is auto-enhance contrast?

It stretches the histogram so the darkest pixels become near-black and the brightest pixels become near-white. It is useful for low-contrast scans and faded photographs.

Are my images uploaded to a server?

No. All processing runs locally in your browser using HTML5 canvas. The original file never leaves your device.

What is the maximum supported file size?

Up to 20 MB per file. Supported formats: JPG, PNG, WebP, GIF (first frame only), BMP.