Before you invest in image optimization

It comes up on almost every project, usually later than it should. Before you spend anything on image optimization, it is worth confirming a few things are already true.

Speed is a feature people notice only in its absence, and then they leave rather than complain. Anything you cannot measure here, you are deciding by taste, which is fine as long as everyone knows it.

Prerequisites

• You can describe the outcome you want in one sentence
• Someone owns it after the work is done
• Images are usually the largest thing on a page
• You have a way to tell whether it worked

Common failure modes

Modern formats cut file size substantially at the same quality. That sounds obvious written down. It is still the thing most often skipped. Anything you cannot measure here, you are deciding by taste, which is fine as long as everyone knows it.

Serving a 3000px image into a 400px slot is pure waste. None of that requires a large budget, only a decision and someone to own it. Write the reasoning down alongside the decision, because the reasoning is what changes first.

In practice

Performance work is mostly subtraction, which makes it unpopular and effective. 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 any of that sounds like a description of your current setup, it is fixable.