Two modes for two different jobs
Grayscale removes the color but keeps every tone in between, from black to white. It is the mode for photos: portraits, landscapes or pictures with a classic look, where you still want to see the shadows, textures and details.
Pure black and white turns every point of the image either black or white, with no grays. It is the mode for documents, signatures, stamps and ink drawings: text looks sharper and the background comes out clean. Anything transparent in the original becomes white in this mode, so a signature with a transparent background ends up on white.
Documents and signatures that stay sharp when photocopied
A phone photo of a document almost never has a truly white background: there are shadows, yellowish paper and gray patches. When you print or photocopy it, those areas come out as a dirty gray that makes the text harder to read. Pure black and white mode turns that background white and leaves the text black.
The threshold decides at what point a tone becomes black. If the text or signature looks broken or too thin, lower the threshold so it comes out thicker; if the background fills up with black specks, raise it. A couple of tries is usually enough to find the right setting for each photo.
Print in black and white and save color ink
If you are going to print an image on a home printer and do not need color, converting it first to grayscale or black and white lets you see exactly how it will come out and keeps the printer from using the color cartridges. It is handy for school assignments, handouts, tickets, coupons or maps.
For documents, pure black and white is usually the best choice, because it also removes the gray background that uses up ink. For photos you want to keep with all their nuances, use grayscale.
Many images, private and without a watermark
You can convert many images at once, for example every photographed page of a document, and download them in a ZIP. If you then want them in a single file, send them to “JPG to PDF”; if a form asks for smaller files, use “Compress image”.
The conversion happens in your browser: the images never leave your device and we keep no copy. EXIF data is removed when the result is created, including the GPS location. You can keep the original format or save as JPG, PNG or WEBP. It is 100% free, with no sign-up, no usage limit and no watermark.