Which output format should I choose?+−
JPEG is the safest universal choice for photos and supports adjustable quality. WebP typically produces noticeably smaller files at the same visual quality and also supports adjustable quality, but is very slightly less universally supported by older software. PNG is lossless (no quality slider does anything) and is usually a poor choice for photos - it only makes sense for images with large flat areas of color, like screenshots or logos.
Why does resizing the image reduce file size more than adjusting quality alone?+−
File size scales roughly with the number of pixels, so cutting an image's dimensions in half can shrink the file to roughly a quarter of the size - often a much bigger win than lowering quality on the same number of pixels, especially before the quality reduction starts becoming visually noticeable.
Will compressing a PNG actually make it smaller?+−
Sometimes only slightly, since PNG compression is already lossless and this tool doesn't apply advanced PNG-specific optimizations (like palette reduction). If you need PNG's transparency support but want a genuinely smaller file, resizing the image usually helps more than re-encoding alone; if you don't need transparency, switching to JPEG or WebP will shrink it much further.
Will resizing my image distort or stretch it?+−
No - the max dimension slider scales width and height by the same factor, so your photo's proportions are always preserved. It only ever shrinks the image down to fit within that limit; if your photo is already smaller than the chosen max dimension, it's left at its original size.
Why does the reduction percentage show 0% instead of a negative number?+−
Re-encoding can occasionally make a file larger rather than smaller, which tends to happen with small images or ones that are already well-optimized. Instead of showing a confusing negative percentage in that case, the tool simply reports 0% smaller, since there's no real reduction to show.
Can this tool also compress audio files and PDFs, or is it just for photos?+−
Yes - the Image / Audio / PDF switcher above the tool lets you compress all three. Audio files are decoded and re-encoded to MP3 (adjustable bitrate) or WAV (adjustable sample rate, bit depth, and channels) using a real in-browser MP3 encoder. PDFs are shrunk by recompressing their embedded JPEG photos at a lower quality and by cleaning up the file's internal structure; a PDF made up mostly of text or vector graphics won't shrink much, since there are no photos in it to recompress.