This tool decolourizes an image without changing the perceived brightness of its colours. All processing happens entirely in the browser, and your image will not be sent over the Internet.

This tool works by processing the image in a percetually uniform colour space designed to match human senses, instead of the commonly used RGB colour space (or its derivatives HSV and HSL) which matches how electronic screens work, but not how humans see.

If you want to learn more, I recommend reading the following two articles by Björn Ottosson, who designed the colour space used in this tool:

• "How software gets color wrong"
• "A perceptual color space for image processing"