Compress a Signature Image

Why signatures are harder than photos

A signature is made of thin dark lines on a light background. JPG compression works by discarding fine detail, so at a very low file size the lines can turn grey, blur at the edges or pick up speckles around the strokes. A photo of a face hides this much better. The result is that the way you capture the signature matters more than the compression itself.

Capture it well before you compress

1. Use a thick, dark pen. A black or dark blue felt-tip or gel pen gives strokes that survive shrinking. A thin pencil line does not.
2. Use plain white paper with no lines, grid or printed pattern. Flat white areas cost almost nothing in file size; paper texture and shadows eat the budget.
3. Photograph or scan it straight on in even daylight, with no shadow from your phone or hand. A scanner app that flattens the page works too.
4. Crop tightly. Leave only a small white margin around the signature. Every empty pixel you remove leaves more of the size budget for the strokes. The compressor does not crop, so do this first in your phone's photo editor.
5. Sign large. A big signature that is later scaled down keeps cleaner lines than a small one that has to be enlarged or squeezed hard.

Compress it

1. Check the limit box above reads the size your form states. It starts at 20 KB; the 50 KB and 100 KB buttons switch it.
2. If the form lists a maximum width and height in pixels (for example 140 × 60 px), open The form also asks for pixel dimensions and enter the numbers. The image keeps its proportions and fits inside that box, so it may come out smaller than the numbers you typed. To stay under the size limit it can also shrink further than the box you entered, down to a shortest side of 40 px. It is never enlarged or cropped.
3. Drop your signature image on the box, or click it to choose a file.
4. Click the thumbnail to see the result at full size, then click Download.

Check the result before you upload

• Zoom in. Every stroke should be continuous, with no gaps where a thin line has faded out.
• The background should look clean and white. Light grey haze or speckles around the lines suggest the file was squeezed too hard; recapture with a darker pen or crop tighter.
• Look at the dimensions shown in the result. If the form requires exact pixel dimensions, this tool cannot guarantee them.
• If the form also sets a minimum file size, check the size shown in the result. The tool only keeps the file at or under your limit.

20 KB or 50 KB?

Use the limit your form states. If a form gives you a range or does not say, a lower limit is not better for you: a larger file keeps more detail. When a form allows 50 KB, compress to 50 KB rather than 20 KB, and your signature will usually look sharper. The tool does not decide this for you, so read the instructions next to the upload field. For photos rather than signatures, see the 20 KB page and the 50 KB page.

What this tool does not do

• It does not remove or whiten a background. If your photo has a coloured or shadowed background, retake it on white paper.
• It does not crop or straighten the image. It follows the photo's orientation as your camera recorded it, but it does not rotate it any other way.
• It does not draw or type a signature. You need an image of a signature you already made.
• The output is always JPG. Transparent areas turn white. If the form requires PNG or PDF, this tool is not the right fit.

Frequently asked questions

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