Images · Signature Resizer

Resize a signature to 20 KB for exam forms on Mac

Clean up a scanned signature — white paper, dark ink — and fit your form's pixels and KB limit without it going grey.

Runs on your Mac

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Signature Resizer in OneMacTools on a Mac, with sample files and its options

Signature Resizer on a Mac

Signature Resizer in OneMacTools with sample files loaded and the options panel open — Signature Resizer with sample files and its options

The result of Signature Resizer on the sample files — What Signature Resizer produced from the sample files

Screenshots from the app, using sample files.

How to use Signature Resizer

1
Sign on plain white paper
Use a dark pen, then scan it or take a photo straight on in good light.
2
Drop the scan or photo
You can add several signatures at once; each is handled separately.
3
Choose your exam
Pick a preset, or Custom to type the pixel size and KB range from your form.
4
Adjust the clean-up
The default works for most photos. Lower it if faint strokes disappear, raise it if the paper still looks grey.
5
Click Clean & Resize
The signature is cleaned, cropped to the ink, fitted to the size and saved in a dated folder in Downloads › OneMacTools. Check it with the Preview (eye) button before uploading.

What Signature Resizer does

Compressing a phone photo of a signature usually leaves grey, blotchy paper. Signature Resizer pushes the paper to white and the ink to dark first, crops to the signature, then fits the exam's pixel size and KB window. Turn the clean-up down to keep faint strokes, or save a transparent PNG to place on documents.

Great for

Upload a signature to a bank or government exam form
Sign PDFs with a clean signature image
Fix a signature photo taken on paper

Options explained

Exam: IBPS & SBI (bank exams), SSC (CGL, CHSL, MTS, GD), RRB (Railways), UPSC, NTA (NEET, JEE, CUET) or Custom. The presets are common signature sizes from recent notifications; check yours and use Custom if it differs.
Size (px): Only shown when Exam is Custom. The exact width and height your form asks for, such as 140 x 60.
At least (KB): Only shown when Exam is Custom. The smallest file size the form accepts. Leave it empty if there's no minimum.
At most (KB): Only shown when Exam is Custom. The largest file size the form accepts. Required for Custom.
Background clean-up: From 0 to 100%; the default is 50%. Decides how much light grey counts as paper and is turned pure white. Lower it to keep faint or thin strokes, raise it for shadowy phone photos.
Transparent background (PNG, for documents): Off by default. Saves the signature as dark ink on a transparent background, to place on PDFs and documents. PNG can't be tuned to a KB limit, so use the normal JPEG for upload forms.

Best practices

Sign a little larger than usual on the paper. The signature is cropped to the ink and scaled down, so a bigger original keeps more detail.
Photograph the paper straight on, not at an angle, and avoid your own shadow falling across it.
A black or dark blue pen works best. The output is black ink on white, so the pen colour doesn't need to match the form.
Use the transparent PNG for signing PDFs, and the JPEG for exam and bank portals that check KB limits.
If the result looks blotchy, raise the clean-up; if letters break up, lower it and run it again.

Works with

In: A scan or photo of a signature as JPEG, HEIC, PNG or another format your Mac can open.
Out: A JPEG at the exact pixels and inside the KB range, named with “signature” and the size, or a transparent PNG if you turn that on.

If a small signature can't reach the minimum KB even at full quality, the JPEG is padded with an invisible comment inside the file. The picture and pixel size stay exactly as required.
The signature is fitted inside the size without stretching; any spare space is white (or transparent).
Presets are common sizes from recent notifications. Always check your form's current rules.

Questions about Signature Resizer

Why does my signature turn grey when I compress it?

A photo of paper is never pure white, and heavy compression smears that unevenness into grey blotches. Signature Resizer turns the paper white and the ink dark first, so the small file stays crisp.

How do I get a signature under 20 KB?

Choose your exam, or Custom with the size and KB range, and drop a photo or scan of your signature. It's cropped to the ink, fitted to the pixels and saved inside the range.

What size is an IBPS signature?

The IBPS & SBI preset uses 140 × 60 pixels and 10–20 KB, a common size in recent notifications. Check your notification, as it can change, and use Custom if it's different.

Some of my strokes disappear.

Turn the background clean-up down. Faint pen strokes are kept at the cost of a slightly less perfectly white background.

Will my blue ink stay blue?

No. The signature is turned into dark ink on white (or on transparency), which compresses cleanly and is what most forms expect.

How do I make a signature with a transparent background?

Turn on “Transparent background (PNG, for documents)”. You get a PNG of just the ink, ready to place on a PDF or document.

Does Signature Resizer upload my files?

No. Signature Resizer runs entirely on your Mac, so your files never leave it and it works offline.

Will Signature Resizer change my original files?

No. Results are saved as new files in a dated folder in Downloads › OneMacTools, and your originals are left exactly as they were unless you turn on an option that says otherwise.

What does Signature Resizer need?

Just a Mac with macOS 26 or later. There's nothing else to install.