Why is my compressed image still so big?

File size scales with pixel count, and pixel count scales with the square of the dimensions. Halving the width and height leaves a quarter of the pixels, not half.

So a 4000-pixel photograph displayed in an 800-pixel column is carrying twenty-five times the data it can show. Compressing it to quality 60 might halve the file and make it look poor; resizing it to 1600 pixels cuts it by roughly 84% and looks perfect.

If your compressed file is still large, this is the first thing to check and usually the answer.

PNG compresses by finding repetition. A photograph has almost none — sensor noise means neighbouring pixels differ slightly even across a flat sky — so the algorithm has nothing to exploit and stores essentially every pixel.

A 12-megapixel photograph is commonly 15–25 MB as PNG and 1.5 MB as a quality-80 JPEG that looks the same on screen. If your "compressed" file is several megabytes, check whether it is a PNG that should be a JPEG.

The reverse mistake exists too: a screenshot saved as JPEG is often larger than the PNG would be, as well as visibly worse.

Compression exploits redundancy. Once a good encoder has removed it, a second pass finds little — and re-encoding at a high quality can genuinely produce a larger file, because the new encoder must now spend bytes faithfully reproducing the first one's artefacts.

Anything downloaded from a website, received through a messaging app or exported from social media has already been compressed, often aggressively. If a file like that barely moves, the tool is not failing — the file is already near its useful floor. The honest response is to keep the original, or to reduce the dimensions instead.

Some images legitimately need more bytes. Dense foliage, gravel, crowds, textured fabric, film grain and heavy noise all contain genuine fine detail with no repetition, and there is no way to describe it briefly.

A portrait against a plain wall might reach 80 KB at 1600 pixels. A photograph of a forest at the same dimensions may need 250 KB before it stops looking mushy. That is not a failure of the tool; it is the image being genuinely more complicated.

Metadata is a rounding error on a 3 MB photograph and a significant fraction of a 30 KB one.

• EXIF — camera, lens, exposure, timestamps, GPS. Typically a few kilobytes.
• Embedded thumbnails — a small preview stored inside the file, sometimes several kilobytes.
• ICC colour profiles — can be tens of kilobytes for a large profile.
• Editing history — some software stores a surprising amount.

Stripping all of it is one toggle, and on a file with a tight size limit it can be the difference between passing and failing.

If you need an alpha channel, JPEG is out, and PNG is the obvious fallback — but not the smallest one. Lossless WebP carries the same full alpha channel and is typically 25% smaller; lossy WebP with transparency is smaller again.

Every current browser supports it. If the file has to open in older desktop software, PNG remains the safe choice, and you accept the size.