How to use it
- Pick a style.
- For black and white, move the threshold until the picture reads well.
- Add images and download.
Greyscale is not an average
A simple way to remove colour is to average the red, green and blue values. It looks wrong, because our eyes are far more sensitive to green than to blue. A pure blue sky and a pure green lawn would come out the same grey, when to us the grass looks much brighter. This tool weights the channels the way the sRGB standard does, roughly 21% red, 72% green and 7% blue, so brightness relationships in the photo stay natural.
Black and white with a threshold
The Black & white style makes every pixel either pure black or pure white. It is the right choice for signatures, stamps, line drawings and scanned text that needs to look crisp, or for preparing artwork for a laser cutter, vinyl cutter or vector tracing. The threshold decides the cut-off: lower values make more of the picture white, higher values make more of it black.
Sepia
Sepia mixes the colour channels towards warm browns, imitating the toning used on early photographic prints. It suits portraits and old-fashioned invitations more than landscapes.
Questions people ask
Does converting to black and white make the file smaller?
Somewhat. A greyscale JPG compresses a little better. PNG saves more, especially in pure black and white.
Can I get a signature onto a transparent background?
Convert to black and white first, then use the transparent background tool to remove the white.
Which threshold should I use for scanned text?
Start at the default of 128. If thin strokes break up, raise it; if the paper texture shows as specks, lower it.