Why Some Images Become Larger After Compression

A file can come out larger after you press “compress,” even when the tool is working correctly. Compression is an encoding process, not a guarantee of fewer bytes. The source may already be highly optimized, or the new format and settings may simply need more space to represent the picture.

A compressed file can already be efficient

A photograph saved previously as a small JPEG may have very little unused information left for another encoder to remove without visible damage. Re-encoding that picture at a higher quality can produce a larger file. The encoder may also make different decisions about color data and image detail.

For example, an already optimized JPEG might weigh 180 KB. Exporting it at a high quality in another encoder could produce 260 KB. These numbers are hypothetical, not a claim about a particular browser. The point is that the original encoding and the new settings both matter.

Switching formats can increase size

PNG is lossless for its encoded pixels. A complex photographic image exported from JPEG to PNG is often much larger, because PNG is no longer discarding photographic detail in the same way. The process does not reverse previous JPEG damage; it simply stores the decoded pixels in a different format.

WebP often gives useful savings for web images, but its relative size depends on the content, browser implementation and quality setting. A very simple PNG graphic may remain smaller than the WebP version. There is no universal ranking for all images.

Dimensions and transparency matter

If you enlarge an image, the encoder processes more pixels. Increasing a 600 × 400 picture to 1200 × 800 multiplies the pixel count by four. Even a lower quality setting may not offset that change.

Transparency can also affect the result. PNG and WebP can represent transparent pixels, while JPG cannot. When VeyraPixel exports transparent art as JPG, transparent regions become white. That may be acceptable for a white-background document and unsuitable for graphics placed over dark backgrounds.

How to diagnose a bigger output

1. Check the input dimensions beneath the original preview and the output dimensions beneath the processed preview. Unexpected upscaling is a common cause.
2. Confirm the selected output format. If you changed JPG to PNG, a larger file may be expected.
3. For JPG or WebP, try a modestly lower quality setting and compare visual detail, rather than moving straight to the minimum.
4. Process the same original with a different supported format. Keep the dimensions identical for a fair comparison.
5. Read the displayed byte comparison. VeyraPixel shows a percentage larger when output size exceeds input size.

The percent-change calculation

The tool uses the actual input and output byte lengths. It calculates the relative change as (1 − output bytes ÷ input bytes) × 100. If the input is 200 KB and the output is 150 KB, the displayed result is 25% smaller. If the output is 250 KB, it is 25% larger. The calculation is unrelated to the position of the quality slider.

The file may be larger and still be useful if your real goal was conversion or resizing. But if size reduction is the only objective, the sensible choice is often to keep the smaller original rather than forcing a new export.

What not to conclude

A larger result does not prove the tool is broken, and a smaller result does not prove its quality is acceptable. Inspect fine print, edges and gradients, and keep the original source for later work. For a broader strategy, read how to compress without unnecessary quality loss.