A short guide to image optimization

The version of this that works is simpler than the version most people imagine. Everything we would tell a client about image optimization in the time it takes to drink a coffee.

Performance work is mostly subtraction, which makes it unpopular and effective. It is worth deciding this deliberately rather than inheriting whatever the last person set up.

What it costs to ignore

Images are usually the largest thing on a page. The cost of getting this wrong is rarely visible on the day it happens. Write the reasoning down alongside the decision, because the reasoning is what changes first.

The practical version

Modern formats cut file size substantially at the same quality. This is the sort of thing that compounds, quietly, in both directions. Most teams find the first pass takes an afternoon and the maintenance takes minutes a month.

Common failure modes

Serving a 3000px image into a 400px slot is pure waste. In practice this is a scheduling problem more than a technical one. The version that survives contact with a real deadline is the simple one.

The short version

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. 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

If you are not sure where your systems currently stand on this, it takes us about an hour to find out.