Can an image be compressed with no visible change?
Sometimes. Lossless compression reduces redundant data while preserving the decoded pixels. Lossy compression discards some image information to reduce the file further. Whether the difference is visible depends on the picture, output settings, viewing size, and the viewer.
There is no setting that guarantees a smaller file and an identical image for every source. Keep the original until you have checked the output at the size where it will be used.
Choose a format before tuning quality
JPEG is a practical choice for photographs but does not preserve transparency. PNG preserves sharp edges and transparency and is lossless for its pixel data, though a photo saved as PNG can be much larger. WebP and AVIF can represent photographic and transparent images, but compatibility depends on the software that will open them.
Changing formats can alter color, transparency, animation, and metadata. A format conversion is not automatically an improvement; use the format that fits the image and destination.
Check dimensions as well as encoding
A large image contains more pixels than a small display needs. Resizing to the actual display dimensions can reduce file size before compression. Do not resize a source that must remain available at a larger print or display size; keep a full-resolution master.
Compression quality controls a trade-off: lower lossy quality usually makes a smaller file but can introduce blockiness, ringing, or loss of fine texture. Compare at normal viewing size and zoom in on important details.
Use Pixuna’s image compressor
Open the Image Compressor, choose one or more images, and select Start Processing. The current implementation resizes images wider than 1,200 pixels and encodes the result as JPEG at a fixed quality. There is no quality slider or target-size control.
Because the output is JPEG, transparent areas are not retained. The result may also look softer than the original. If transparency matters, use a different workflow such as the image converter and choose PNG or WebP where your browser supports it.
When lossless is important
For screenshots, diagrams, logos, and images with transparent backgrounds, inspect the result carefully and consider retaining a PNG master. For photographs, compare JPEG or modern-format exports and choose the smallest version that still looks acceptable for its intended use.
Pixuna image tools process images in your browser. Check the processing path of any other media tool before selecting a file.