Images & sharing
What is image compression?
Image compression represents image data using fewer bytes, with a choice between preserving that data exactly and discarding some detail to reduce the file size further for a particular use.
By Plainview WebReviewed
The meaning
Lossless compression preserves the image data it encodes; lossy compression discards some information. PNG uses lossless compression, typical website JPEGs use lossy compression, and WebP supports both approaches. The useful choice depends on the picture: fine text and sharp diagram edges can reveal damage that is less obvious in a photograph.
Resizing is a separate decision. It changes the number of pixels, while compression changes how image data is stored. A smaller export can combine both. Saving a resized image as PNG does not restore the pixels removed during resizing, even though the PNG encoding itself is lossless.
An example
Preparing a photo for an article
Suppose a fictional article has a 4,000 × 3,000 pixel source photo and its publishing template calls for a 1,200 × 900 pixel export. Keep the original, resize proportionally, then compare an accepted JPEG or WebP output. Those dimensions describe this example, not a universal website requirement.
Inspect the actual download for fine edges, faces, gradients and any text. Compare its byte size as well as its appearance. If the image needs transparency, choose an output that supports it; a JPEG export needs a solid background instead.
When it matters
A suitably prepared image can reduce the data a page needs to transfer while preserving the detail visitors need. File size alone cannot establish a page-speed improvement: the page’s other resources, loading behavior and delivery also matter.
Plainview’s Image Compressor & Resizer processes one supported image in the browser and shows the exported result. For JPEG or WebP, you can choose quality or try a target file size. If the target is not reached, review the result and consider smaller dimensions or another suitable format.
A common confusion
An 80% quality setting does not mean 20% fewer bytes
Quality is an instruction to the encoder, not a promised saving. Image content, format and browser behavior affect the result. An export can even be larger than its source. Choose from the measured size and visible quality of the downloaded file, and retain the original for future exports.