Image optimization: what to get right first

We end up explaining this on discovery calls often enough that it deserved writing down. If you only fix one thing about image optimization this quarter, make it the first item below.

Performance work is mostly subtraction, which makes it unpopular and effective. If two people in the business would answer this differently, that gap is the actual problem.

Start here

Images are usually the largest thing on a page. That sounds obvious written down. It is still the thing most often skipped. Check it against what you would want a competitor's site to get wrong.

Then this

Modern formats cut file size substantially at the same quality. Small and consistent beats large and occasional here. It is worth deciding this deliberately rather than inheriting whatever the last person set up.

Eventually

Serving a 3000px image into a 400px slot is pure waste. The reasoning matters more than the rule, because the rule has exceptions. Check it against what you would want a competitor's site to get wrong.

How to tell if yours is fine

Speed is a feature people notice only in its absence, and then they leave rather than complain. Three things worth confirming about image optimization before you move on:

• Someone can say what the current setup is without going to look
• Modern formats cut file size substantially at the same quality — and you know whether that is true here
• There is a way to tell whether the last change to this helped

Pick the one that would hurt most if it failed, and start there.