How to Reduce Image File Size Without Losing Quality
A single phone photo can be 5 MB or more. Here is how to shrink it by 80–95% and still have it look good.
Step 1: Resize first
Most of the size comes from pixels you do not need. A 4000-pixel-wide photo displayed in a 1200-pixel column wastes more than 90% of its data. Scale the picture to the largest size it will actually be shown at, such as 1920 px for a full-width banner or 1200 px for a blog image.
This is the single biggest saving, and it costs nothing in visible quality.
Step 2: Pick the right format
Photos belong in JPG or WebP, never PNG. A photo saved as PNG is often ten times larger. If you have a PNG photo, converting it to WebP or JPG is the biggest win. Keep PNG for logos, screenshots and graphics with flat colors.
Step 3: Lower the quality a little
Quality 75–85 is the sweet spot for most pictures: the file shrinks dramatically while you can barely see a difference. Below about 60 you will start to see blocky patches and fuzzy edges. Compare before and after at 100% zoom, not in a thumbnail.
Step 4: Hitting an exact limit
Forms that demand 'under 200 KB' are common. Resize to roughly 1000–1200 px on the long side, compress at quality 70, and check the size. If it is still too large, drop to 800 px or lower the quality in steps of 5.
What to avoid
Do not compress the same JPG again and again; every pass loses a bit more. Always compress from your original. Do not enlarge small pictures to fix blur, since it only makes them softer.