July 15 2023

The Importance of Adaptive Images in Web Performance and Core Web Vitals

Understanding the Impact of Adaptive Images: How Careful Use of Images Can Revolutionize Website Performance and Improve Core Web Vitals Metrics

We live in a digital age dominated by the web, where the design and performance of a website or application are of vital importance. These two components work in synergy, forming the foundation of the user experience. Good website performance is not only a desirable goal, but a prerequisite that can directly influence the success of a site or an application. A site that works efficiently and quickly provides a more pleasant experience, encourages users to stay longer, and increases the likelihood that they will take a desired action, such as making a purchase or signing up for a service.

In this vast and complex scenario, adaptive images play a decisive role. Efficient image management is a crucial aspect of optimizing website performance, as images make up a significant portion of a web page's total weight. Adaptive images, in particular, can lead to significant improvements in page loading speed and overall user experience.

In this article, we will delve into the world of adaptive images, examining how they work, their importance in the context of Core Web Vitals – the set of metrics introduced by Google to evaluate user experience – and how they can help improve the user experience, particularly in contexts where the internet connection is slow or unstable, such as on 4G or 3G networks.

This detailed review will allow us to understand the significant impact that adaptive images can have on a website's performance and its ability to provide an optimal user experience. Regardless of the type of internet connection you use, a positive user experience can be the difference between the success and failure of a website or web application.

What are the Core Web Vitals?

Google, in its relentless pursuit to improve and optimize user experience on the web, has introduced i Core Web Vitals, a foundational set of metrics destined to become an essential reference for web developers and professionals. These metrics offer a quantitative and qualitative view of user experience, focusing on crucial aspects such as loading, interactivity and visual stability of web page content.

I Core Web Vitals they include Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS), each of which is designed to measure and quantify a distinct and fundamental aspect of user experience.

Core Web Vitals


Il LCP is a metric that measures the time taken for the largest block of content visible within the user's viewport to load. It is an essential indicator of the perceptual loading speed of a page, giving an idea of ​​how long a user has to wait before seeing the substantial content of the page.

Il IN, on the other hand, deals with quantifying the interactivity of a page. Measures the time between when a user interacts with a page (for example, clicking a link or button) and when the browser is able to respond to that interaction. This metric is critical to understanding how responsive a page is from a user's point of view.

Finally, the CLS focuses on the visual stability of a page. This metric calculates the sum total of all unexpected layout shifts that occur while visiting a page. This is especially important to ensure that users don't make incorrect interactions due to unexpected content movement.

Each of these metrics provides deep insight into the key elements that contribute to user experience on the web, enabling industry professionals to optimize their pages in a more targeted and effective way. THE Core Web Vitals they therefore represent a fundamental tool for anyone aiming to provide a high-quality user experience, making them an essential element of the modern web ecosystem.


Regarding the Core Web Vitals we have written several specific articles about what are i Core Web Vitals, as well as how do you optimize i Core Web Vitals.

Adaptive images and their impact on Core Web Vitals

Adaptive images represent an innovative and effective technique for optimizing the performance of web pages, making the user experience more fluid and enjoyable. This method involves generating and distributing several variants of the same image, each optimized for a specific device resolution. This image optimization process is done using several techniques, including lossless compression, resizing, and changing the image format.

When a user accesses a web page, the web server detects the resolution of the user's device and delivers the most appropriate image version. For example, a user on a lower resolution mobile device will receive a smaller, lighter version of the image, optimized for their device. This image will have an adequate pixel size and quality to ensure an excellent viewing experience without overloading your device's bandwidth or resources. Conversely, a user on a higher resolution desktop device will receive a larger, more detailed version of the image.

This adaptability approach has a significant impact on Core Web Vitals by Google, a set of metrics intended to evaluate the quality of the user experience on a web page. A case in point is the impact of adaptive images on the Largest Contentful Paint (LCP), a metric that measures the time it takes to load the largest content element visible on the page. By using adaptive images, the overall image size is reduced for lower resolution devices, resulting in faster LCP, as device-optimized images take less time to load.

Additionally, adaptive images can help reduce First Input Delay (FID), another Core Web Vital metric that measures the amount of time between the user's first input (for example, a click or tap) and the browser response. A browser can respond more quickly to user interactions if it isn't overwhelmed with loading and rendering large images. Consequently, using lighter versions of the images for lower resolution devices can significantly improve the FID.

Finally, using adaptive images can also help keep Cumulative Layout Shift (CLS) low, a metric that evaluates a page's visual stability by preventing unexpected layout shifts. Providing images that are appropriately sized for the user's device and resolution can prevent unexpected expansion or shrinkage of visuals, resulting in lower CLS and a more stable and predictable user experience.

Advantages of adaptive images

Adaptive images bring significant benefits to any website, but these benefits are greatly magnified for users with slow or unstable network connections, such as those provided by 3G or 4G networks. These benefits are multiple and have a direct impact on page loading speed, quality of user experience and, consequently, site engagement and conversion metrics.

First, it's vital to understand that images make up a significant portion of a web page's total weight. In some cases, they can account for more than 50% of the total page size. Reducing image weight through image size optimization can, therefore, have a drastic impact on the loading speed of a page.

This reduction in page weight has a direct and significant effect on user experience. For users with slow or unstable connections, downloading large images can result in long loading times, creating interruptions and delays that can frustrate users and cause them to abandon the site. The use of adaptive images can significantly reduce these loading times, allowing a page to load faster and smoother.

For example, take a web page that contains a large image intended to be viewed on a desktop at a resolution of 1920×1080. This image could easily be 2 MB or more in size. However, on a mobile device with a resolution of 480x320, an optimized version of this image may only be 200KB in size. This is a 90% reduction in image size, which results in a significant reduction in page load time, especially on a 3G or 4G connection.

Furthermore, when adaptive images are implemented correctly, the visual quality of the images is not compromised. This means that mobile users not only benefit from faster loading times, but also receive images that have been optimized for their specific screen resolution, thus ensuring optimal visual quality.

Improve user experience with optimized images

The use of adaptive images, in addition to significantly reducing loading times, has the ability to elevate the quality of the user experience in various and relevant ways. In particular, an image that is properly optimized for a mobile device will appear sharper, more detailed, and more visually appealing on that device than a large image that is simply scaled down.

This is because when a high resolution image is scaled to fit a lower resolution display, fine detail can be lost and the image can appear blurry or pixelated. On the other hand, an adaptive image is created specifically for the target resolution, preserving sharpness and detail. This implies that the display of the image on the mobile device will have an optimal quality, contributing to a more attractive and professional site design, and therefore to a superior user experience.

Additionally, the use of adaptive visuals can go a long way in ensuring that content is presented appropriately and consistently across different devices. This is especially important in today's era, where web browsing is done from a variety of devices, from high-resolution desktops to mobile devices with smaller screens and different resolutions.

For example, an image that is perfectly formatted and viewed on a desktop may not maintain the same presentation quality on a mobile device if it has not been properly optimized. It could be too big, too small, or it could alter the layout of the page in unintended ways, all of which can degrade the user experience. An adaptive image, on the other hand, maintains its visual quality and placement regardless of which device you're viewing it on, ensuring a consistent, high-quality experience across all devices.

From a technical point of view, this is accomplished using various tools and techniques, such as the HTML5 picture element, various source attributes and CSS media queries, which allow you to specify different versions of an image for different screen resolutions or services of self-hosted CDNs or PaaS or SaaS.

The use of adaptive images is not only a performance optimization strategy, but also a key element in providing a superior user experience, regardless of the device used for navigation. This holistic approach enhances the site's visual appeal, ensures content consistency across devices, and ultimately encourages user engagement and loyalty.

Fixed "Use images of adequate size" error with adaptive images

Another common error that can be encountered when analyzing a website with Google PageSpeed ​​Insights is "Use adequately sized images". This warning occurs when images uploaded to the site are larger than the actual size required by the site's layout on a given device. In other words, the image is too large for the space it should occupy, causing an unnecessary waste of download data and rendering resources.

This problem can be solved effectively through the use of adaptive images. When we use techniques such as the 'srcset' attribute in the image tag or the 'picture' element, we can provide the browser with different versions of the same image at different resolutions. The browser then selects the most appropriate image based on the viewport size and pixel density of the user's device.

Use properly sized images

For example, if an image needs to occupy a 500px wide space on a page layout in a mobile device, it doesn't make sense to serve a 2000px wide image that would take up four times as much width and, consequently, a much larger volume of data to download. Instead, with the use of adaptive images, we can deliver a 500px wide image specific to those devices, thus reducing the amount of data needed to download the image and saving resources for rendering.

This approach ensures that only the appropriately sized images are served, optimizing data usage and improving site load times. As a result, it resolves the "Use images of adequate size" error reported by Google PageSpeed ​​Insights, helping to improve the site's overall performance score.


The relevance and effectiveness of adaptive images in the context of web and video performance Core Web Vitals it is an element that cannot be overlooked or underestimated. This image management methodology proves to be not only strategic, but essential for obtaining appreciable results in terms of website performance and optimization.

The main appeal of adaptive images lies in its ability to offer a number of key benefits that help significantly improve the user experience. These include significantly reducing page load times, a crucial element in today's era where speed equals efficiency and success. A website that loads quickly is more appealing to the user, encourages more interaction, and as a result, leads to higher conversions and customer loyalty.

In addition, the use of adaptive images helps optimize the user experience by ensuring that the images displayed are of the most appropriate size, resolution and format for the specific device the user is using. This ensures not only visual consistency, but also the appropriateness of the content for various types of devices, from high-resolution desktops to smaller mobile devices.

This approach provides a personalized experience for the user, regardless of the device used, ensuring the highest visual quality and smooth interaction. This becomes even more relevant in today's multi-device digital landscape, where a consistent, high-quality user experience across all devices is paramount.

In conclusion, if your goal is to improve the performance of your website, increase user engagement and ensure a high-quality user experience, implementing adaptive images should be a central element of your optimization strategy. Their positive impact on loading speed, user experience, and content consistency across various devices makes adaptive images an indispensable tool in every web developer and designer's toolkit.

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