Most "my image looks wrong" problems are really format problems. The three formats people actually argue about — PNG, JPG, and WebP — are not interchangeable; each wins a specific job.
JPG (JPEG) is for photographs. It throws away detail you can't see to make files dramatically smaller, which is perfect for camera shots and anything with smooth gradients. The cost: it's "lossy," so saving it again and again degrades it, and it has no transparency. Use JPG for photos on the web and in presentations.
PNG is for graphics with sharp edges, text, or transparency — logos, screenshots, icons, diagrams. It's "lossless," so it stays crisp at any zoom and supports see-through backgrounds. The cost: PNG files of photos are huge. If your logo has a transparent background, PNG is the only safe choice of the three.
WebP is the modern web default. For the same look it's usually smaller than both JPG and PNG, and it supports transparency and even lossless mode. The catch is older software and some print pipelines don't accept it, so keep a PNG or JPG original as the master.
Decision: photo → JPG; logo/screenshot/transparency → PNG; web delivery where supported → WebP (keep a PNG master). To switch, the Image Converter tool flips between PNG, JPEG, and WebP in your browser with no upload. Then the Image Compressor tool resizes and re-qualities the result so it's small enough to load fast — again, entirely on your device.
Quick path: know what the image is, pick the format by the rule above, convert, then compress to about 75–80% quality for the web. Private end to end.