Core Web Vitals measure three things: how fast the main content appears, how stable the layout stays, and how quickly the page answers input. On a portfolio, the first photograph usually decides all three.
LCP: the largest element first
On an image page the largest element is an image. It needs loading priority, a size appropriate to the device, and a genuine intermediate state — a low-resolution placeholder in the same geometry beats empty space.
CLS: never without an aspect ratio
Every image needs width and height, or an aspect-ratio in CSS, or text jumps as it loads. This is the most common fault in hand-built galleries and one line fixes it.
INP: JavaScript is the bottleneck
Elaborate scroll effects block input processing. Keep animations to transform and opacity, register scroll listeners as passive, and even older phones stay under the recommended 200 milliseconds.
Measure instead of guessing
A lab Lighthouse score is an approximation. Field data from real visitors is what counts, and it shows that mobile networks and older devices set the real bar — not the machine in the studio.