PNG compression behaves differently from a JPEG quality slider. When the goal is truly lossless optimization, the compressor is not allowed to throw away image detail just to reach a smaller number.
That means a valid result can be dramatically smaller, slightly smaller, unchanged, or occasionally a little larger.
PNG compression is lossless
A lossless PNG optimizer searches for a more efficient way to encode the same decoded pixels. It can change filters, compression choices, metadata, and internal representation, but the visible pixel result must remain the same.
imgevoke's PNG compression path removes the specific metadata chunks supported by the current implementation and then runs OxiPNG. The production browser tests compare decoded pixels for the test fixture before and after optimization.
Already optimized files have less room to improve
Many PNG files have already passed through an optimizer before they reach you. Design exports, build pipelines, app stores, and other image tools may have removed easy inefficiencies already.
Running another lossless optimizer cannot invent savings that no longer exist. If the new encoding is not smaller, imgevoke reports No size reduction instead of pretending that compression succeeded.
Metadata can help, but pixels usually dominate
Text comments, timestamps, and EXIF-style metadata can add unnecessary bytes. Removing supported metadata may reduce the file, but metadata is often only a small fraction of a large photographic PNG.
The pixel data still has to be represented without loss. A complex image with gradients, noise, texture, or photographic detail can remain large even after a careful optimization pass.
If the dimensions are larger than needed, Resize Image can remove unnecessary pixels before you optimize the file.
When converting format is the better move
If you need a substantially smaller file and do not require PNG's lossless characteristics, format choice may matter more than another optimization pass.
For a photograph, a JPG or lossy WebP version can often be much smaller because those formats are allowed to discard some image information. For an image that needs transparency, WebP may be worth comparing with PNG.
Use Image Converter to create an alternate format and compare the real outputs. Keep PNG when its lossless pixels or transparency are important; change format only when that trade-off fits the use case.