JPEG vs PNG: which format should you actually use

Neither is universally better; the right answer depends on the content. PNG preserves every pixel exactly, so it is the higher-fidelity format by construction. JPEG is lossy and discards image data to reach a smaller file, so the saved file is not pixel-identical to the source. For photographs the loss is imperceptible at quality 75 and above; for graphics the same loss visibly degrades sharp edges and text. Use PNG when fidelity matters more than file size; use JPEG when the content is a photo and the byte saving matters.

Use PNG for graphics with sharp edges - logos, icons, UI screenshots, line art and text - and for any image that needs a transparent background. PNG is lossless, so the saved file is identical to the source, and PNG carries an alpha channel, which JPEG does not. The MDN Image file type and format guide describes transparency and lossless compression as the two defining traits of PNG. Use JPEG for photographs instead, where the file size saving of lossy compression outweighs the per-pixel fidelity.

No. JPEG cannot carry an alpha channel at all. Any image saved as JPEG that had transparency in the source will be composited on a solid background before the JPEG is written. The MDN Image file type and format guide lists transparency as a format capability that JPEG explicitly does not have; PNG and WebP do. If you need transparency in the saved file, choose PNG (lossless, alpha preserved) or WebP.

No. The file extension is just a label; the format is determined by the bytes inside the file. Renaming image.jpg to image.png produces a file labelled .png that still contains JPEG bytes, which most viewers and browsers will either reject or display with the wrong colours. If you actually want transparency, re-encode the image in PNG or WebP from the source. The Image Compressor here keeps the source format exactly so the output never silently changes the format on you.

It depends on the image, not the destination. Use JPEG for photos on the page; use PNG for graphics, screenshots and anything that needs transparency. For the smallest payload at the same visual quality, consider a WebP version of either - web.dev's modern-formats guide recommends WebP and AVIF for web delivery because they are typically smaller than JPEG and PNG at comparable visual quality. The WebP vs JPEG page on this site covers that follow-up decision in detail.

Quality 80 on Pillow's 0 to 100 scale is the balanced default that most tools and tutorials settle on, including Beita Image's Image Compressor. Quality 75 is a reasonable lower bound for web photos; quality 90 and above is near-visually-lossless and is the right choice for archive or print. Below 60 the 8x8 block artefacts become visible at normal viewing distance. The Pillow JPEG encoder documentation is the canonical reference for the quality scale.