Imagine you're reading a long magazine article with dozens of pictures. When you first open the magazine, you can only see the pictures on the current two-page spread—the rest are on pages you haven't turned to yet. Offscreen images on your website are similar: they're the images that aren't immediately visible when your page loads because they're below the fold (the part of the page users need to scroll down to see) or in carousel slides that aren't currently active.
By default, browsers load all images on a webpage when it first loads, regardless of whether they're visible or not. This means your visitors are downloading images they might never see if they don't scroll down, or images they won't see until later when they click through a gallery or slider.
Loading all images immediately, even those offscreen, can significantly impact your website's performance:
The impact is especially significant on mobile devices or slower connections, where downloading multiple large images can delay the entire page from becoming usable. In fact, images typically make up the largest portion of a webpage's size—often 50-80% of the total bytes downloaded.
Lazy loading is a technique that defers loading offscreen images until they're about to come into view as the user scrolls down the page. Here's how it works:
The result is a faster initial page load, better resource utilization, and an experience that feels smoother and more responsive to users—all without them noticing that some images weren't loaded initially.
The concept of prioritizing content "above the fold" (visible without scrolling) comes from newspaper design, where the most important headlines appeared on the top half of the front page—the part visible when the newspaper was folded on a newsstand. On websites, this area remains crucial for making a good first impression and should load as quickly as possible.
Implementing lazy loading for offscreen images provides several important advantages:
For image-heavy websites like e-commerce stores, portfolios, or news sites with long articles, lazy loading can dramatically improve performance without sacrificing visual quality.
Before implementing lazy loading, it's helpful to assess how many offscreen images your pages have and their impact:
When assessing offscreen images, pay attention to:
Modern browsers now support native lazy loading without requiring custom JavaScript.
Simple fix: Add the loading="lazy" attribute to image tags that are below the fold: <img src="image.jpg" loading="lazy" alt="Description">. This simple addition tells the browser to defer loading until the image approaches the viewport.
For more control or to support older browsers, you can use the Intersection Observer API.
Simple fix: Instead of loading image src directly, use data-src to store the image URL, then use Intersection Observer to detect when images are near the viewport and swap data-src to src. Many lazy loading libraries use this approach under the hood.
Blank spaces while images load can create a jarring experience as users scroll.
Simple fix: Show a very small, blurred version of the image (1-5KB) immediately, then replace it with the full-quality image when it comes into view. This technique, known as LQIP (Low-Quality Image Placeholder), provides visual context while waiting for the full image.
Some images might be important enough to load quickly but still benefit from optimization.
Simple fix: Use progressive JPEGs for important images, which load in increasing quality. The image appears quickly at low quality, then improves as more data loads, rather than displaying nothing until the entire image is downloaded.
Many CDNs offer built-in image optimization and lazy loading features.
Simple fix: Consider using an image-focused CDN like Cloudinary, Imgix, or Cloudflare Images that can automatically implement lazy loading and serve optimized images in modern formats like WebP.
If you need more sophisticated features or broad browser support, lazy loading libraries can help.
Simple fix: For WordPress sites, plugins like a3 Lazy Load or WP Rocket include lazy loading features. For custom sites, libraries like lazysizes or lozad.js provide advanced lazy loading with broad browser support.
What's happening: Lazy-loaded images cause the page layout to jump when they appear because their dimensions weren't reserved.
Simple solution: Always include width and height attributes on image tags, or use CSS to establish aspect ratios for image containers. This reserves the correct space even before the image loads.
What's happening: Images start loading only when they enter the viewport, causing users to see blank spaces briefly as they scroll.
Simple solution: Set a larger threshold for your lazy loading trigger so images begin loading when they're near the viewport, not just when they enter it. Using an offset of 200-300px typically provides a good balance.
What's happening: You're worried search engines might not index lazy-loaded images properly.
Simple solution: Use the native loading="lazy" attribute or implementation methods that keep the img tag in the HTML with its proper alt text. Modern search engines understand lazy loading and can index these images correctly.
What's happening: If your lazy loading relies entirely on JavaScript, users with JavaScript disabled won't see images beyond the initial viewport.
Simple solution: Implement lazy loading with the noscript tag as a fallback that provides standard img tags for users with JavaScript disabled. Native loading="lazy" also works without JavaScript in supporting browsers.
Implementing lazy loading for offscreen images impacts several key performance metrics:
| Performance Metric | How Lazy Loading Affects It |
|---|---|
| Page Load Time | Dramatically reduces initial load time by downloading fewer resources up front |
| Time to Interactive (TTI) | Improves TTI by reducing the amount of data that needs to be processed before the page becomes interactive |
| Largest Contentful Paint (LCP) | Can improve LCP if your largest content element is an above-the-fold image that now loads faster due to reduced competition for bandwidth |
| Cumulative Layout Shift (CLS) | May increase CLS if not implemented properly, but with correct image dimension handling, can maintain or improve CLS |
| Total Blocking Time (TBT) | Reduces TBT by spreading out the processing of images instead of handling them all at once during initial load |
The key benefit is that lazy loading transforms a heavy, single burst of activity at page load into a more distributed, as-needed approach that better aligns with how users actually consume content.
Companies that have implemented lazy loading for offscreen images have seen significant performance improvements:
These examples demonstrate that lazy loading offscreen images can provide substantial benefits across different types of websites, directly improving both performance metrics and business results.
Lazy loading offscreen images follows a simple but powerful principle: only deliver what users need when they need it. Just as a smart restaurant doesn't prepare every dish on the menu when you walk in the door, your website shouldn't load every image when a visitor first arrives—only what they can see immediately.
The beauty of lazy loading is that it creates a win-win situation. Your visitors get a faster, more responsive website that uses less of their data plan, while you benefit from reduced server load, lower bandwidth costs, and improved performance metrics that can help with search engine rankings.
Best of all, when implemented correctly, lazy loading is virtually invisible to users. They simply experience a website that loads quickly and responds smoothly as they scroll, without realizing that images are being loaded just in time as they're needed.
With native browser support now available and multiple implementation options for different needs, there's no reason not to implement lazy loading for offscreen images on your website. It's one of the easiest and most effective performance optimizations you can make, with benefits that extend to nearly every aspect of the user experience.
Greadme's easy-to-use tools can help you identify offscreen images on your website and provide simple, step-by-step instructions to implement lazy loading—even if you're not technically minded.
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