Think image optimization will improve your Core Web Vitals and PageSpeed Insights score? Think image compression is enough to make your pages load faster?
Well, contrary to what you may have already heard, this is largely false! Stéphane Rios, CEO of Fasterize, formerly CTO of Rue du Commerce, and with more than 10 years of careful observation of market developments and best practices, deconstructs preconceived ideas.
What is the impact of image optimization on loading speed compared to other webperf techniques?
Stéphane Rios : To answer this question objectively, we conducted a test on an e-commerce site in the mass retail sector. The results are clear: while optimizing images is essential, it is not enough to maximize loading speed. Even if image optimization does part of the work, it is the activation of all the levers that can significantly boost performance !
We notice that with the optimization of images alone, the LCP is improved, the weight of the images too, but the evolution of the PageSpeed Insights score and other metrics is not obvious.
Comparison table of performance between a non-optimized web page,
with only images optimized, and with 100% of resources optimized by Fasterize
Optimizing images would be just another good practice for loading speed?
SR : Yes! Concretely, image optimization impacts 15 to 20% of a site’s performance . However, logically, to optimize 100% of performance, you have to apply… 100% of webperf techniques .
And you have to be able to put everything together to make it effective, keep up to date with the evolution of best practices, techniques and formats, maintain optimizations over time… Hence the interest in automating everything.
In practice, web performance is a vast and complex field that touches on all the technical aspects of a website: HTML code, JavaScript, CSS, fonts , third-party scripts , server response time , cache management, etc.
And you also need to know how to prioritize the loading of content on a page to reinforce the impression of speed, to be able to manage load peaks, etc.
Images are only part of the many levers for webperf optimization. It is the fact of activating them all and articulating them intelligently that has a real impact on loading speed
Images represent 40 to 50% of the weight of pages , so reducing their weight is an indisputable lever to improve loading times. This is also one of the recommendations of PageSpeed Insights .
But when you see the long list of tips and everything there is to do to speed up page loading, you understand that compressing images and making them responsive is one of the ways to optimize your web performance, but it is not the alpha and omega. Web performance is not just about optimizing images, it is about optimizing all the code and all the resources.
In other words, an image optimization solution alone cannot push performance scores to the maximum. In reality, image optimization is a commodity in the same way that a Content Delivery Network ( CDN ) is, for example.
Excerpt from PageSpeed Insights’ list of recommendations
for optimizing loading speed.
Image optimization is one of the tips… among many others.
But then, what about the impact of image optimization on Core Web Vitals and PageSpeed Insights score?
SR : Compressing and resizing images does not improve all Core Web Vitals. This may be disappointing, but it is a technical reality.
As I just pointed out, compressing images is not going to improve all web performance metrics to the maximum extent.
It will not even have any impact on some metrics, notably CLS and FID.
Compressing images doesn’t improve CLS?
SR : Image compression does not contribute to a good Cumulative Layout Shift (CLS ) score , the Core Web Vitals metric that assesses the visual stability of a page.
Why? Because optimizing CLS requires, among other things, reserving a space of the right dimensions for images, so that the content remains stable on the page during loading. Compression reduces the weight of files, resizing allows images to be adapted to different screen sizes, but as you will have understood, it does not address the issue of visual stability!
And image optimization doesn’t improve FID either?
SR : No! The First Input Delay (FID) , is also part of the Core Web Vitals, and it evaluates the responsiveness of pages. And the culprit for poor page responsiveness is… JavaScript, not images !
You can compress your images to the best formats, it can have an effect on the FID, but it remains really very minimal compared to what the optimization of the scripts brings.
In short, optimizing only part of the resources (for example, images) means taking the risk of only partially improving the Core Web Vitals and SEO , and above all, it means missing out on the business potential of your site!
In this case, how can you equip yourself to optimize 100% of your resources?
SR: Plugins or solutions exist for caching static pages, asynchronous loading of JavaScripts, image optimization, etc. These tools optimize one aspect of web performance; at best, they address a selection of levers.
Additionally, a solution that only optimizes part of the resources may force you to accumulate tools or plugins to make a site really fast.
This is potentially the beginning of a counterproductive spiral, because accumulating tools to cover all needs involves setting them up individually, and checking that all optimizations work and are articulated correctly. Finally, since each tool has a price, multiplying them inflates the budget.
Conversely, a complete solution like Fasterize’s Next-Gen CDN covers 100% of the needs to sustainably optimize all the pages of a site , rationalizes costs , and centralizes the management of all optimizations with a single tool, to automatically articulate them in order to maximize their effectiveness.
So, the promise of activating optimization with a single click is all well and good. But activating all the techniques at once to push the quality of the user experience, SEO and conversions to the maximum is much better!
Concretely, what are the advantages of Fasterize compared to an image optimization solution?
SR : Fasterize is a real webperf toolbox that automatically applies all the optimizations needed for a fast site, from the most basic to the most advanced.
In addition, it simplifies access to all the latest generation techniques and formats, not only to optimize images on the fly, but also all resources.
For a site that is already optimized, and for which only the images remain to be processed, you should know that Fasterize:
- provides access to the best compression formats – including WebP, which is recommended by Google – but also AVIF , which is more recent and even more efficient, and which is not offered by all image optimization solutions ;
- obviously offers compression options for classic formats (JPEG, Progressive JPEG, GIF, PNG, SVG);
- provides automatic resizing and smart cropping ;
- applies lazyloading correctly to optimize Largest Contentful Paint (LCP);
- improves visual stability of pages (CLS);
- analyzes users’ browsing context for automatic choice of the best image version (compression format and dimensions);
- provides caching and a CDN role ;
- and guarantees ultra-responsive support and expert assistance to meet the most complex business and technical challenges
… in addition to optimizing all the code, to boost all the Core Web Vitals, the PageSpeed score, and all the business and technical KPIs!
Test the impact of optimizing images and all your resources for free with our SaaS solution:
