Lossy vs. lossless compression
Learn how lossy and lossless settings affect a shop photo, a screenshot, and other common web images.
Compression is a tradeoff between representation and bytes
An image file stores pixel data along with format and metadata information. Compression encodes that data using fewer bytes. “Compressed” alone does not tell you whether decoded pixels are unchanged, whether the image looks different, or whether the output is smaller than the input. Those results depend on the encoding method and image content.
There are two broad families. Lossless compression allows the encoded image to be decoded back to the same pixel values. Lossy compression intentionally discards or approximates some visual information, often achieving smaller files at the cost of possible visible differences. Both can be appropriate when chosen for the job.
Lossless: exact decoded pixels
PNG is a familiar lossless format. It can preserve crisp lines, flat-color graphics, and transparency without introducing lossy encoding artifacts. Lossless compression does not mean every source becomes tiny. A photograph has complex texture and color variation that may be difficult to represent compactly without approximating detail. It may therefore remain large as PNG.
Lossless output is useful when exact pixel values matter: screenshots with small text, artwork where a changed edge is unacceptable, or a working file that will be edited repeatedly. It is also useful as a clean intermediate. But it cannot recover details that were already lost in a source JPEG; it only preserves the decoded pixels it receives.
Lossy: controlled approximation
JPEG is a common lossy format. It can make photo files smaller by approximating image details, but discarded information cannot be recovered from the export. Stronger compression usually makes visible artifacts more likely. A quality setting does not correspond to the same perceived result across formats or encoders.
Artifacts often appear around sharp edges, repeated patterns, and smooth gradients. You may see block boundaries, ringing, smearing, or banding. At a small display size, these effects may be difficult to notice; at a close zoom they can become obvious. The best setting depends on the image and viewing context, so inspect the actual export.
Do not confuse dimensions with compression
Resizing and compression are separate operations. Resizing changes the number of pixels. Compression changes how those pixels are encoded. If a 4000-pixel-wide image will only appear 800 pixels wide, reducing dimensions may remove far more unnecessary data than pushing quality to a very low setting. Conversely, an image intended for a full-screen display may need its original dimensions even if it can be compressed efficiently.
A practical order is to decide the required display dimensions, then choose an output format and compression method. Change one variable at a time and compare the result. If the image is a photo, test a lossy output. If it is a graphic with sharp text or transparency, try a lossless choice. Keep an original in case you want a different export later.
What MEZENCORE does
MEZENCORE lets you adjust quality, target file size, and maximum dimensions. Compressed downloads do not keep EXIF camera details. Images are processed in your browser, so large files can exceed the memory available on a device. The largest workable file depends on the image and device.
The output can be larger than its input, especially when converting an already optimized image or asking for an unsuitable format. The interface reports the result so you can decide whether to keep it. For a clearer selection process, read how to reduce image size and which format to choose, then try the tool with a copy of your image.