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Getting a signature or small image under 20 KB
Application forms often want a scanned signature between 10 and 20 KB. A signature is dark ink on a plain background, which compresses very well once the image is a sensible size.
We shrink the pixel dimensions and JPEG quality together, down to 800 pixels on the longest side at the smallest setting, and keep the gentlest step that fits under 20,000 bytes.
Tips
- Sign in dark ink on plain white paper, and crop tightly around the signature before uploading.
- Take the photo in good light so the paper comes out white rather than gray. A clean background takes far fewer bytes.
- If the form also asks for exact pixel dimensions, check them. We shrink to hit the file size, not to a specific width and height.
Questions
What pixel size does a signature end up at when it is squeezed under 20 KB?
We step the longest side down from 4000 pixels to 800 and keep the first step that fits under 20,000 bytes. An image already smaller than a step keeps its size, because we never enlarge it, so a 600-pixel-wide signature crop stays 600 pixels wide and only its JPEG quality drops.
Why does a cropped signature strip fit in 20 KB more easily than a photo of the whole page?
At the smallest step the longest side is 800 pixels. A signature strip cropped to 800 x 200 pixels holds 160,000 pixels, while a 4:3 photo of the page at 800 x 600 pixels holds 480,000. The same 20 KB is then spread over a third as many pixels, so less quality has to be given up.
What do I get if my signature scan still will not go under 20 KB?
The last step is 800 pixels on the longest side at JPEG quality 35. If the file is still over 20 KB there, you get the smallest version we made, with a note that it did not reach the target. Crop closer to the ink and use whiter paper, then upload again; a cleaner background takes fewer bytes.
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