Reducing image size without losing quality: what that really means
, 5 min read
Strictly speaking, making an image smaller always removes something. The useful question is whether anyone can tell, and the answer depends on which of two very different operations you use.
Resizing changes dimensions
Resizing reduces the number of pixels. A 4000 pixel wide photo shown on a 1080 pixel wide phone screen is carrying nearly four times the detail that can be displayed. Cutting it to 1600 pixels throws away information you were never seeing, which is why Resize Image is usually the first thing to try.
Compressing changes how pixels are stored
Compression keeps the dimensions and stores the detail more economically. JPEG does this by discarding fine colour variation that the eye handles poorly. At quality 75 the result is generally indistinguishable from the original on screen, while the file may be a fifth of the size. Push to 40 and you start seeing blockiness in skies and skin.
The order that works
- Resize to the largest size you actually need: about 1920 pixels wide for a website or presentation, 1080 for social media.
- Compress at quality 75 to 85 with Compress Image.
- Check the result at full size before using it.
Two things that quietly ruin images
Repeated saving. JPEG loses a little each time it is saved. Editing and re-saving the same photo five times leaves visible damage. Always work from the original.
The wrong format. Screenshots and text saved as JPG get fuzzy halos around letters. Use PNG or WEBP for those, and see Image Converter to switch.
If you want to estimate sizes before committing, the Image File Size Calculator shows what given dimensions typically produce.