How Do You Optimize Images For Core Web Vitals?

Story Based Question

You’re working on optimizing your website for SEO and realize that Core Web Vitals are a major ranking factor for Google. You know that slow load times and poor user experiences can hurt your rankings, especially when it comes to images. As you dive deeper, you realize that images are often the main culprits behind poor performance metrics like Largest Contentful Paint (LCP).

Now you’re wondering: How do you optimize images to improve Core Web Vitals and boost your rankings?

Exact Answer

To optimize images for Core Web Vitals, ensure that images are compressed, served in next-gen formats (like WebP), responsive, lazy-loaded, and properly sized for different devices. By reducing image size, improving load times, and optimizing how images load, you improve LCP and overall user experience, positively impacting SEO.

Explanation

Google’s Core Web Vitals are a set of user experience metrics that directly affect how your site ranks in search results. Two of these metrics, Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS), are heavily impacted by images.

Here’s how each metric connects to image optimization:

1. Largest Contentful Paint (LCP)

LCP measures the time it takes for the largest visible element on a page to load. If this element is an image and it’s slow to load, your LCP score will suffer. Slow images are often caused by large file sizes or improper compression.

To optimize LCP for images:

• Compress images to reduce file sizes without losing quality.
• Use next-gen formats like WebP that are more efficient at maintaining quality at smaller file sizes.
• Serve responsive images with the srcset and sizes attributes, ensuring images are sized appropriately for different screen sizes.
• Preload key images (e.g., hero images) so they load faster and improve LCP.

2. Cumulative Layout Shift (CLS)

CLS tracks unexpected layout shifts, which happen when content moves around as it loads. For example, an image that loads late and pushes other elements down can cause a layout shift.

To prevent CLS caused by images:

• Set explicit width and height for images in your HTML or CSS to prevent layout shifts.
• Use CSS to ensure images maintain their aspect ratio so they don’t mess up the layout as they load.
• Avoid using large, off-screen images that push other content as they load.

3. First Contentful Paint (FCP)

While FCP is primarily focused on text or other elements, images also play a role. If images are the first visible elements on your page, they should load quickly to contribute to a good FCP score.

Best Practices for Optimizing Images for Core Web Vitals

1. Compress Images
   Use tools like TinyPNG or ShortPixel to reduce file size without losing quality. This helps images load faster, improving LCP.
2. Use Next-Gen Image Formats
   Convert images to formats like WebP or AVIF, which are more efficient and load faster than traditional formats like JPEG and PNG.
3. Responsive Images with srcset and sizes
   Use srcset to serve different image sizes based on the device’s screen size. For example, a mobile device should load a smaller image than a desktop, saving bandwidth and improving load times.
   
   <img src=”default.jpg” srcset=”image-400.jpg 400w, image-800.jpg 800w, image-1200.jpg 1200w” sizes=”(max-width: 600px) 400px, (max-width: 1200px) 800px, 1200px” alt=”Optimized image”>
   
4. Lazy Load Off-Screen Images
   Implement lazy loading so that images only load when they’re visible in the viewport. This can improve LCP by reducing initial load times.
   
   <img src=”image.jpg” loading=”lazy” alt=”Lazy-loaded image”>
   
5. Preload Key Images
   For important images (like hero images), use the <link rel="preload"> tag to tell the browser to load them early in the page load process, speeding up LCP.
   
   <link rel=”preload” href=”hero-image.jpg” as=”image”>
   
6. Optimize Image Dimensions
   Always specify image dimensions (width and height) in your HTML or CSS. This ensures the browser knows how much space to allocate, preventing layout shifts and improving CLS.
7. Use a Content Delivery Network (CDN)
   A CDN stores images on multiple servers around the world, delivering them from the server closest to the user. This reduces latency and helps speed up image delivery, improving load times and LCP.

Example

Let’s say you run an e-commerce website. Your homepage features a large hero image, several product images, and a gallery. Without optimization:

• Your hero image is slow to load, causing a delayed LCP and poor user experience.
• Product images are large and uncompressed, slowing page load times and increasing bounce rates.

After optimizing for Core Web Vitals:

• You compress all images and switch to WebP for better compression.
• Use srcset to serve appropriately sized images for mobile and desktop users.
• Implement lazy loading for all images below the fold.
• Preload the hero image to improve LCP.
• Add image dimensions to prevent layout shifts.

Result:

• Your page now loads faster and is more responsive.
• LCP improves, so Google ranks you higher.
• Bounce rates drop, and users stay on your site longer.

Optimizing images is one of the best ways to improve Core Web Vitals and overall site performance. By compressing images, using next-gen formats, implementing responsive images, and focusing on speed and layout stability, you can significantly boost both user experience and SEO.