Compress Image to 20KB

Why 20 KB Needs Small Dimensions

20 KB is 163,840 bits. A JPEG photo needs roughly 0.5 bits per pixel to look good and around 0.25 bpp to look acceptable. So a 20 KB photo can comfortably describe 300,000–650,000 pixels at most, and far fewer if it has a busy background. That is roughly 500 × 650 pixels. A modern phone photo has 12 million pixels or more.

Forms that set a 20 KB limit know this, and nearly always specify small dimensions too, such as 200 × 230 pixels for a photo or 140 × 60 for a signature. Follow those numbers, and 20 KB is generous. The table above shows the budget for common sizes.

Preparing a Signature Step by Step

Signatures are the most common 20 KB upload, and also the easiest to get right.

• Sign clearly: dark blue or black pen on plain white paper, larger than you normally would.
• Capture evenly: photograph from directly above in daylight or scan it; avoid shadows from your phone.
• Crop tightly: leave only a small margin around the strokes.
• Clean the background: increase brightness and contrast, or convert to grayscale, so the paper reads as white.
• Resize: match the form's dimensions or keep it around 300–600 pixels wide.
• Compress: add it here with the 20 KB target.

Preparing a Photo for 20 KB

Use a recent, front-facing photo against a plain light background. Plain backgrounds compress to almost nothing, leaving the budget for your face. Crop to the shape the form asks for, which is often passport-like proportions, then resize to its pixel dimensions. If you need an official-style photo, the Passport Photo Maker helps with framing and background colour before you compress.

Avoid compressing an image that was already heavily compressed by a messaging app. Artefacts from the first compression add noise that the second compression struggles with, wasting your tiny budget.

How the Engine Handles Tight Targets

The compressor runs a binary search over JPEG quality, encoding and measuring up to nine times. It keeps the largest result that still fits under 20 KB, stops early once it lands within a few percent below the limit, and never hands you a file above the limit when a fitting quality exists. When an image is too large to fit even at minimum quality, you get a warning that tells you to resize, instead of a file the portal would reject.

Grayscale, Contrast and Clean Backgrounds: Free Bytes

At 20 KB, every byte the encoder spends on something you do not care about is a byte taken from what you do. The biggest hidden cost is usually the background. Off-white paper with a shadow, a textured wall, or sensor noise from a dim room is full of tiny random variations, and JPEG has to describe them all. A pure white background, by contrast, is almost free: an 8 × 8 block of identical pixels compresses to a handful of bits.

For signatures and text documents, convert to grayscale with the Grayscale Converter unless the form demands colour. JPEG then has only one channel to encode instead of three, and colour noise from indoor lighting disappears. Raise contrast slightly so the ink is darker and the paper whiter. For photos, choose a plain, evenly lit background when you take the picture; it is far easier than fixing it afterwards.

These steps often make the difference between a blotchy 20 KB file and one that looks clean. They also make the result more consistent if you need to repeat the process for several documents.

Local Processing for Sensitive Uploads

A signature is a security credential. It should not be uploaded to unknown websites for compression. ImageMagix processes it in your browser: the file is read, compressed and saved locally, and no copy is sent anywhere. The output also contains no EXIF metadata.