How Converting a PDF to Grayscale Reduces Its Size

If a colour scan won't compress small enough, converting it to grayscale is often the trick that gets you under the limit — with no loss of legibility for text documents.

Why grayscale is smaller

Colour images store three channels (red, green, blue) per pixel; grayscale stores one. That alone cuts image data substantially, and grayscale also compresses more efficiently.

When to use it

Use grayscale for documents where colour isn't needed — most forms, certificates, and text scans. Keep colour only when it carries meaning (like a colour-coded chart or a photo ID where colour matters).