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How to Preload Largest Contentful Paint Image and Improve Web Performance

Did you know that 88% of online shoppers won’t return to a website after having a bad user experience? Web performance is a crucial factor for the success of any website, as it affects user satisfaction, engagement, and conversion. Largest Contentful Paint (LCP) is a metric indicating web performance by timing how long the page’s largest element, often an image, takes to load and display. Preload largest contentful paint image can bolster a website’s load speed and user experience.

Optimizing LCP images involves balancing strategies like preloading and lazy loading. While preloading speeds up critical images, it may consume more bandwidth. Lazy loading reduces needless requests but can delay crucial image rendering. Hence, choosing the best method requires evaluating each option’s benefits and drawbacks.

The main research question of this article is: How does preloading LCP images affect web performance and user experience? To answer this question, we conducted an empirical study using websites and user data. 

Table of Content

Understanding preloading LCP images

preload largest contentful paint image

Largest Contentful Paint (LCP) is a metric that reflects how fast a webpage loads from the user’s perspective. It tracks the time it takes for the largest element on the page, usually an image or a text block, to appear on the screen. According to web performance statistics, 47% of users won’t wait longer than two seconds for a website to load, so optimizing LCP can improve user satisfaction and retention.

When we talk about “LCP images,” we’re referring to the images on a webpage that the LCP metric considers. This is usually the largest image or text block visible within the viewport. If an image is the largest contentful element, it would be regarded as the “LCP image.” Optimizing this LCP image (for example, reducing its file size or using specific loading techniques) can improve the LCP score and thus the perceived load speed of the webpage.

Preloading LCP images involves loading these critical visual elements of a webpage in advance, thereby reducing perceived loading time and ensuring a smooth browsing experience. This section delves deeper into the importance of preloading LCP images and explores various aspects of its implementation.

The significance of preloading LCP images

  • Preloading LCP images plays a vital role in improving page load speed, which is a crucial factor in user satisfaction and engagement.
  • By loading the most significant visual content first, preloading LCP images enables users to see meaningful content quickly, reducing the risk of bounce rates and enhancing the overall user experience.

How preloading LCP images works

  • Preloading LCP images involves initiating the loading process for these images as early as possible, preferably during the initial stages of page loading.
  • When Preloading is implemented correctly, browsers fetch and store LCP images in the background, making them readily available when the user reaches that part of the webpage.

Benefits of preloading LCP images

  • Improved perceived loading time: Preloading LCP images reduces the perceived loading time by eliminating delays in rendering critical visual elements.
  • Enhanced user engagement: Faster loading of LCP images leads to higher engagement, as users can quickly interact with and consume content.
  • Optimal user experience: By prioritizing loading LCP images, Preloading ensures a smoother browsing experience, minimizing frustrations caused by slow loading times.

Understanding the concept and benefits of preloading LCP images sets the foundation for effective implementation. The following section will explore the impact of preloading LCP images, shedding light on the importance of testing and measuring their performance.

Evaluating the impact of preloading LCP images

An essential aspect of improving website performance is understanding the repercussions of our implemented strategies. Measuring the impact when preloading Largest Contentful Paint (LCP) images provides insights into its effectiveness.

Methodology and data sources used for the evaluation

The evaluation process involves a comparative study of web performance metrics before and after the implementation of LCP image preloading. Tools like Google’s Lighthouse and Chrome DevTools are incredibly useful in generating performance reports. These reports provide metrics such as LCP time, First Contentful Paint (FCP), and Time to Interactive (TTI).

Utilize Chrome DevTools to analyze

In addition, Google Analytics or similar platforms can also provide user engagement metrics like bounce rate, session duration, and conversion rates. This data helps us understand the practical impact on user experience.

To ensure the reliability of the evaluation, the tests should be carried out multiple times under similar network and device conditions. The aggregate data will then give us a comprehensive understanding of the impact.

Analysis of results and findings

Once we gather the data, the analysis phase begins. Here, we compare the web performance metrics before and after preloading LCP images. An effective preloading strategy will show improvements in the metrics, primarily marked by a decrease in LCP time. You may also witness reduced FCP and TTI, as Preloading can aid faster rendering and quicker page interactivity.

Furthermore, improved LCP scores may correlate with better user engagement metrics. For instance, decreasing bounce rates or increasing session durations post-preloading would suggest an enhanced user experience.

Comparing performance metrics of pages with and without preloading LCP images

A comparative study of performance metrics of pages with and without Preloading can solidify our findings. Pages that employ Preloading should, theoretically, outperform in LCP times than those that don’t.

However, the comparison needs to be fair and take into account other optimizations that might be in place. For example, a page not using Preloading might utilize different performance-boosting strategies, such as next-gen image formats or a Content Delivery Network (CDN). Therefore, other factors should be kept constant to get an accurate measure of the impact of preloading alone.

We can draw definitive conclusions about its effectiveness by accurately evaluating the impact of preloading LCP images. Not only does this help us make informed decisions regarding its implementation, and it enlightens us about how this strategy contributes to enhancing overall website performance and user experience.

How to preload Largest Contentful Paint image

Enhancing a website’s performance requires keen attention to detail and effective implementation of various strategies. One such critical strategy is preloading LCP images. While we’ve already discussed what Preloading is and how it impacts performance, let’s dive deeper into the practical implementation of this technique.

Boosting website performance via LCP image preloading

The fundamental technique: using the ‘link’ tag 

When it comes to preloading resources, the most straightforward technique involves using the `` tag in the HTML document’s `` section. This tag has attributes that can be adjusted to indicate the type of content and its location. For preloading an image, we would set `rel=”preload”` and `as=”image”.`</span></p>

Here is an example of how you can instruct the browser to preload an image:


<link rel=”preload” as=”image” href=”path/to/image.jpg”>


This code snippet tells the browser to start loading the image early during the page load. It does so in a non-render blocking manner, meaning the rest of your webpage will continue to load simultaneously. This parallel loading process can significantly reduce the LCP time and enhance the user experience.

Advanced preloading: leveraging JavaScript

While using the `` tag is simple and effective, situations may call for more dynamic preloading decisions. JavaScript comes in handy for such scenarios. For instance, you might want to preload an image only if a user has a certain preference enabled or is using a specific type of device. 

Here’s how you could dynamically preload an image using JavaScript:


var preloadLink = document.createElement(“link”);

preloadLink.href = “path/to/image.jpg”;

preloadLink.rel = “preload”;

preloadLink.as = “image”;



This code snippet creates a new `link` element, assigns the appropriate attributes, and then appends this new element to the document head. This way, the image begins loading in the background, offering the benefits of preloading in response to user-specific conditions.

Beyond preloading: the ‘Intersection Observer’ API 

Sometimes, your LCP image might not be immediately visible when the page loads. For example, the image might be placed “below the fold,” referring to the portion of the webpage that becomes visible only when a user scrolls down. Preloading such an image might not always be the best strategy, as it could compete with other critical resources that are needed sooner.

A more sophisticated API called the Intersection Observer comes to the rescue in these scenarios. This API allows you to configure a callback that fires when an element enters or exits the viewport. This way, you can start loading an image just before it becomes visible, optimizing the loading process without negatively impacting the LCP.

Here’s a basic example of how to use the Intersection Observer API:


var observer = new IntersectionObserver(changes => {

  for (let change of changes) {

    if (change.isIntersecting) {

      change.target.src = change.target.dataset.src;




}, {});



In this code, we first create an Intersection Observer that fires a callback whenever a tracked element — in this case, an image — enters the viewport. When this happens, the image’s `src` attribute is set, causing it to start loading. After this, the observer stops watching the image, freeing up resources.

The art of prioritizing preloads

While Preloading can significantly boost performance, it’s also crucial to remember that balance is key. Preloading too many resources can congest the network, causing more harm than good. Prioritizing what you preload is essential to ensure that critical resources aren’t delayed.

Over-preloading can congest networks

The general rule of thumb is preloading the most critical resources directly contributing to your LCP and overall user experience. Identifying these resources might require some thorough analysis and user behavior understanding. 

Effective Preloading of LCP images isn’t about preloading every image but rather about identifying and preloading the right ones that contribute to a swift and seamless user experience. Combining these methods tailored to your specific needs, you can effectively preload LCP images, leading to a noticeable improvement in your website’s performance.

Remember, performance optimization is an ongoing process. As web technologies evolve, new and improved preloading techniques will become available. Stay updated, keep testing, and keep optimizing for the best results.
<h2>Best practices for optimizing LCP images

After exploring effective techniques for preloading LCP images, let’s transition into best practices for optimizing these images. These go beyond Preloading, aiming to ensure that images load efficiently and contribute positively to user experience and overall web performance.

1. Reducing image size: compress your images

One of the most practical and straightforward methods to improve image load times is through compression. Image compression works by reducing the image’s file size without significantly degrading its quality, a process known as lossless compression. In cases where a slight reduction in image quality is permissible, lossy compression can significantly reduce file sizes.

Numerous tools, such as TinyPNG or Squoosh, are available online, which provide an excellent balance between image quality and file size reduction. Keep in mind, the smaller an image’s file size, the quicker it loads. This results in a faster LCP, thereby improving the perceived speed and performance of your website.

2. Catering to device variations: use responsive images

A one-size-fits-all approach doesn’t work for images in our increasingly mobile world. The image that looks good on a 4K monitor might not be suitable for a mobile device. Responsive images solve this problem by providing the browser with multiple image sizes and allowing the browser to choose the most suitable one, depending on the user’s device and viewport.

This technique can be implemented using the `srcset` attribute in the `img` tag. This ensures that users on different devices receive appropriately sized images, conserving bandwidth for mobile users and ensuring sharp images for desktop users.

3. Optimizing load times: implement lazy loading

As discussed earlier, not every image on a page needs to be loaded immediately. Some images, particularly those “below the fold” or outside the initial viewport, can be loaded as users scroll down. This lazy loading technique can significantly reduce initial load times and improve your LCP.

Lazy loading images outside the initial viewport reduces load times

JavaScript libraries such as Lozad.js provide efficient lazy loading solutions, but you can also use the native `loading=”lazy”` attribute in the `img` tag, supported by most modern browsers.

4. Embracing modern formats: leverage Next-Gen image formats

While JPEG and PNG are widely used, next-generation image formats like WebP and AVIF offer superior compression and quality characteristics. They can provide the same quality as traditional formats but at significantly lower file sizes, resulting in faster load times.

However, browser compatibility should be taken into account. Not all browsers support these newer formats, so ensure you have fallbacks in place using the `picture` element or leveraging the `type` attribute in your `source` elements.

5. Enhancing delivery speeds: use a Content Delivery Network (CDN)

It is a network of servers located across the globe, designed to deliver web content to users more quickly. By serving images from the server geographically closest to the user, a CDN reduces network latency, speeding up the delivery of images and improving your LCP.

6. Streamlining image rendering: optimize image rendering

Rendering images isn’t just about load times. How an image is displayed can also impact user experience and LCP. By specifying the **‘width’** and **‘height’** attributes on your img tags, you can avoid layout shifts, leading to a better Cumulative Layout Shift (CLS) score.

You can also use CSS aspect ratio boxes to reserve space for an image based on its aspect ratio, ensuring that the page layout isn’t disrupted when the image loads.

All these practices form part of a comprehensive performance optimization strategy. 

They focus on images, typically the largest elements on a webpage, and thus likely candidates for LCP. However, remember that LCP could be a text block or video poster image. Always analyze your pages to identify your actual LCP and optimize it accordingly.

A blend of effective preloading techniques and this optimization best practices will ensure that your LCP image loads quickly and benefits overall page performance and user experience. New optimization techniques will arise as technology evolves, so staying updated and continuously testing is vital for maintaining and improving web performance.

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In this article, we have explored the landscape of Largest Contentful Paint (LCP) images, their preloading techniques, and optimization best practices. We’ve uncovered how these concepts collectively contribute to enhancing the perceived speed of a website and the overall user experience.

Effectively managing LCP images isn’t a one-size-fits-all solution; it requires a mix of the right technology and an understanding of user needs. When used appropriately, Preloading can help deliver a rich and engaging user experience without compromising performance. Complementing preloading with image optimization techniques can further streamline this process.

Remaining current, conducting tests, and adopting new methods remain crucial in sustaining and enhancing web performance. The goal remains to strike the perfect balance between delivering high-quality content and ensuring a seamless, quick user experience.

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With over a decade of experience crafting innovative tech solutions for ecommerce businesses built on Magento, Jacker is the mastermind behind our secure and well-functioned extensions. With his expertise in building user-friendly interfaces and robust back-end systems, Mageplaza was able to deliver exceptional Magento solutions and services for over 122K+ customers around the world.
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