Image size has two dials — dimensions and quality. Change them in the right order and the picture still looks good.
| Metric | Before | After |
|---|---|---|
| File | photo.jpg | photo.jpg |
| Dimensions | 4000 × 3000 | 2000 × 1500 |
| Quality | 92 | 62 |
| Size | 4.8 MB | 1.2 MB |
A phone photo these days is 4,000 pixels wide and several megabytes. If its only job is a web page, an email, or an upload form, that's a lot of wasted bytes — and wasted bytes mean slow pages and rejected uploads.
The good news is that file size has only two dials, and you control both.
Dial one: dimensions
Halving the width and height of an image cuts its pixel count to a quarter. Resize first because it's the largest, least harmful lever. A 4000 × 3000 photo scaled to 2000 px wide is a fraction of the file, and at typical viewing sizes nobody can tell the difference.
Dial two: quality
JPG quality is a percentage that trades file size for detail. High values (90+) preserve fine detail at a large cost; values around 60–70 usually look fine for photos on screen.
The trap is turning quality down before resizing, or both at once — you end up blurry with no size benefit. Do it in order, then check.
A realistic before and after
Here's what the two dials do to a real phone photo:
- Original: 4000 × 3000 px, quality 92 — about 4.8 MB.
- After resize to 2000 px wide and quality 62: about 1.2 MB.
- You lose visible sharpness only if you print it. For screens, uploads, and listings, it's the same picture.
When to stop compressing
Stop when the file does its job and the preview still looks right. If you can see banding in skies or mush in fine lines, back the quality up by 10 and re-check. The right size is the smallest one you can't tell from the original at its actual display size.