P0Issue #74

Largest Contentful Paint (LCP) image subparts

❓ What does it mean?

❓ What is it? When Google measures LCP, it often uses an image (e.g., hero banner, product photo, featured image) as the largest visible element. However, if the image is not fully optimized, subparts of the image (like different chunks loaded progressively, or responsive versions) can delay the LCP time. In short: 👉 Instead of the full image appearing at once, Google sees different subparts (tiles or segments) loading slowly, which increases LCP.

✅ How to Fix It

❌ Example of Poor LCP (Image Subparts Problem) A homepage has a large hero banner (1500px wide, 500KB JPEG). The image loads progressively (baseline JPEG), meaning it first appears blurry, then slowly sharpens in multiple steps (subparts). Google tracks the LCP only when the final subpart is rendered → LCP = 4.5s. Result: Poor Core Web Vitals score and higher bounce rate.

❌ Bad Example

✅ Example of Good LCP (Optimized Image) The same hero banner is converted into WebP (150KB). Preloaded in <head> to prioritize loading. Explicit width and height attributes are set to avoid layout shifts. Image loads in one step → LCP = 1.8s. Result: Fast LCP, good UX, and SEO boost.

✅ Good Example

🛠 How to Fix LCP Image Subparts Issues Use Next-Gen Formats – Convert images to WebP/AVIF for faster decoding. Preload Critical Images – Use <link rel="preload" as="image"> for hero/above-the-fold images. Avoid Progressive JPEGs – They cause multiple rendering passes (subparts). Set Correct Dimensions – Always define width and height attributes to reduce CLS + speed up rendering. Use Responsive Images – <img srcset> to serve smaller images for mobile. Lazy-Load Non-Critical Images – Use loading="lazy" for below-the-fold content.

⚡ Result

📈 SEO & UX Impact Faster LCP times → better Core Web Vitals → higher rankings. Reduced bounce rates (users see content quickly). Improved mobile performance, especially on slow connections.