Compress Image to 10 KB

Ten kilobytes is a typical cap for scanned signatures and thumb impressions on exam, recruitment and banking forms, and for tiny profile thumbnails. At that size a phone photo has to lose most of its pixels, so this tool keeps JPEG quality at 50% or more and reduces the width and height until the file fits. A greyscale option makes signature scans smaller still. Files never leave your device.

How to use this tool

1. Add the signature scan or photo (several at once is fine).
2. Keep the maximum at 10 KB, and enter the minimum if the form gives a range such as 4–10 KB.
3. Tick greyscale for signatures and ink scans; enter an exact width and height if the form asks for one (for example 140 × 60 px).
4. Download the file and check the byte count shown under it before uploading.

Formula

For each candidate size, the quality q is found by binary search between 50% and 92% so that size(q) ≤ limit. If even 50% is too big, the pixels are scaled by about 0.95 × √(limit ÷ size) and the search repeats.

File size grows roughly with the number of pixels, which is why the sides shrink by the square root of the size ratio. Greyscale uses the Rec. 601 luma weights 0.299 R + 0.587 G + 0.114 B.

Example

A form asks for a signature of 140 × 60 px between 4 KB and 10 KB. In safe mode the file must be 4,096–10,000 bytes (4 × 1,024 to 10 × 1,000). A clean signature at that size is usually well under 4 KB even at top quality, so the tool adds invisible comment bytes until the JPG is exactly 4,096 bytes and reports "Within limit: Yes".

Getting a readable signature under 10 KB

Sign with a dark pen on plain white paper, scan or photograph it in good light, and crop tightly around the ink before compressing. Greyscale removes the colour information that a signature does not need, and a plain white background compresses to almost nothing, leaving the bytes for the strokes.