JPG, PNG, WebP and AVIF: An Image Compression Guide
Compare JPG, PNG, WebP and AVIF. Learn when to compress, convert or resize images, how to check quality and why smaller files matter.
How do JPG, PNG, WebP and AVIF differ?
JPG and JPEG are two common extensions for the same format, often used for photos without transparency. PNG offers lossless compression and transparency. WebP and AVIF also support transparency and offer alternatives for web delivery. No format wins for every image. Choose according to the destination, the image content and the application that needs to open it.
Why does image compression matter?
Oversized files increase the amount of data a page transfers and can delay images, particularly on mobile connections. A lighter product photo or blog cover can deliver the same content with less data. That is an opportunity to improve the experience, not a guarantee of a particular search ranking or speed score. Identify the oversized images first, then evaluate file size alongside visible quality.
Compression, conversion and resizing are different tasks
Compression concerns encoding, conversion changes the output format, and resizing changes pixel dimensions. Astrotor lets you combine these settings. For example, reduce a 6000 × 4000 photo to dimensions suited to its destination and then export WebP. Renaming a file to .webp is not conversion: its contents must be encoded in that format. A different extension alone does not guarantee a smaller file.
Which format should I try first?
Start with Astrotor’s default WebP setting and test the result in your destination application. Compare JPG when broad sharing compatibility matters, PNG for a lossless output, or AVIF to try another size–quality balance. AVIF can take longer to process on your device. Do not choose by savings percentage alone: inspect small text, hair, foliage and sharp edges as well.
Does converting to PNG improve quality?
No. Saving a JPG as PNG cannot restore details already lost. Astrotor does not use a quality slider for PNG; it optimizes a lossless PNG output. That does not improve the source and can increase file size. PNG remains useful when changing format, preserving transparency or adjusting dimensions. Check both the appearance and the actual file size before downloading.
Prepare the image on your device with Astrotor
Open the image compressor, choose a file and set the output format. If needed, limit its longest edge or enter dimensions. After selecting Process images, compare the actual before/after file sizes and inspect details at 100%. Download the result individually or collect several results in a ZIP. This tool does not upload your files to a server. For help choosing dimensions, read the image resizing guide.