Are my images uploaded?

No. Pixels are read and rewritten with the canvas getImageData / putImageData API in your browser. The image never leaves your device.

How accurate are the colours?

The default uses the ITU-R BT.601 luminance formula (0.299R + 0.587G + 0.114B), which matches how the eye perceives brightness and is the standard for greyscale conversion. A simple-average option is also provided.

What is the difference between the two greyscale modes?

Perceptual luminance weights green most and blue least, giving natural-looking results. The simple average treats all channels equally, which can look flatter but is faster to reason about.

Image to Grayscale

Convert images to black & white or sepia — privately, no upload.

Convert images to grayscale or sepia, privately

Turn any photo black and white, or apply a warm sepia tone. The default greyscale uses the perceptual luminance formula (0.299R + 0.587G + 0.114B, ITU-R BT.601) so the result looks natural rather than washed out.

Every pixel is processed with a <canvas> on your device — your image is never uploaded — and the result downloads as a lossless PNG.