What happens when you compress JPG photos?
A JPG stores a photo in small blocks of pixels. Lowering the quality simplifies fine texture and tiny color shifts inside those blocks. At sensible settings you cannot tell. Push too far and blocky patches show up in skies, with soft halos around text.
Not every photo reacts the same way. A busy market scene hides compression well, while a portrait against a smooth wall shows it sooner. That is why two photos at the same setting can end up very different in size.
Avoid compressing the same JPG again and again, because each save throws away a little more. Keep the original and always work from that copy.
To judge the result, look at it at normal size on the screen where it will be seen. Zooming to 400% shows flaws nobody else will notice.
Which quality setting fits your photo?
| Situation | Try this |
|---|---|
| Ten photos for a work email | 60% to 70% |
| Blog or shop photos | Resize to the column width, then 75% to 80% |
| Portfolio or photos to print later | 85% to 95% |
| Online form with a size limit in KB | Use a preset such as compress to 100 KB |
Pixel size matters as much as quality. A phone photo is often 4000 pixels wide. Halving the width leaves a quarter of the pixels, which cuts the file more than any slider position.
Building a website? WebP is usually smaller than JPG at a similar look, and JPG to WebP converts your photos. Have a PNG screenshot that should be a JPG? Use PNG to JPG first.