Case Study: Boosting Page Speed by 62% with Image Optimization for Core Web Vitals

Case Study: Boosting Page Speed by 62% with Image Optimization for Core Web Vitals

By Satyam Shah•Wed Jul 23 2025•6 min read

Case Study: How Optimizing Images for Core Web Vitals Increased Our Page Speed by 62%

In today's digital landscape, a fast-loading website isn't just a luxury; it's a necessity. Google's Core Web Vitals (CWV) metrics have reinforced this, directly influencing search rankings and, more importantly, dictating the quality of user experience. We understood this imperative, which led us to undertake a comprehensive image optimization initiative for one of our content-rich blog sections, leveraging our very own Image Resizer and Image Converter tools. The results were transformative, demonstrating a significant uplift in page speed and overall site performance.

Understanding Core Web Vitals and Image Impact

Before diving into our strategy, it's crucial to understand why image optimization is so vital for Core Web Vitals. These metrics measure real-world user experience aspects of page loading, interactivity, and visual stability.

Largest Contentful Paint (LCP)

LCP is perhaps the most directly impacted CWV metric by unoptimized images. It measures the time it takes for the largest content element visible within the viewport to load. On many web pages, this largest element is often an image – whether it's a hero image, a featured image, or a prominent graphic within the content. A large, unoptimized image can significantly delay LCP, leading to a poor user experience and a lower Core Web Vitals score. Our goal was to drastically reduce this load time.

First Input Delay (FID) & Cumulative Layout Shift (CLS)

While images don't directly affect First Input Delay (FID) as much as JavaScript execution, a faster overall page load (driven by optimized images) can free up the main thread sooner, indirectly benefiting FID. Similarly, Cumulative Layout Shift (CLS) can be impacted by images that load without proper dimension attributes, causing content to jump around. By pre-optimizing and providing correct dimensions, we could mitigate such shifts.

Our Challenge: A Content-Heavy Blog Section

Our blog section is a cornerstone of our content strategy, featuring numerous articles, guides, and case studies. However, as our content grew, so did the size of our pages, primarily due to large, high-resolution images.

The Problematic Pages

We identified several high-traffic blog posts that were particularly image-heavy. These pages contained multiple large featured images, in-content graphics, and comparison screenshots, all contributing to bloated page sizes. Each article typically hosted 5-10 images, ranging from 500KB to over 2MB each.

Initial Performance Metrics

Before our optimization efforts, these pages exhibited concerning performance metrics according to Google PageSpeed Insights:

  • Largest Contentful Paint (LCP): Averaged 4.8 seconds, putting us firmly in the "Poor" category.
  • Total Page Size: Averaged 6.5 MB, with images accounting for over 70% of that size.
  • Image File Size: Sum of image sizes per page averaged 4.5 MB.
  • Google PageSpeed Insights Score: Consistently in the 30s-40s for mobile.

This presented a clear barrier to user engagement and search engine visibility.

Our Strategy: Leveraging ToolsTol's Image Optimization Suite

Our approach was systematic, focusing on reducing image payload without compromising visual quality. We turned to our own suite of tools for efficiency and effectiveness.

Step 1: Image Resizing with Our Free Image Resizer

The first crucial step was ensuring our images were served at the correct dimensions. Often, images were uploaded at much larger resolutions than needed for display on the web.

We used our free Image Resizer to:

  • Downscale high-resolution source images to their maximum display dimensions (e.g., a 4000px wide image scaled down to 1200px for blog content).
  • Create responsive image variations for different screen sizes, though the primary focus was reducing the largest version.

This immediately slashed file sizes before any compression even began.

Step 2: Format Conversion to WebP with Our Free Image Converter

Next, we addressed the image format. Traditional formats like JPG and PNG are often less efficient than modern alternatives.

We leveraged our free Image Converter to:

  • Convert all our existing JPG and PNG images to the WebP format. WebP offers superior compression, typically resulting in 25-34% smaller file sizes than comparable JPGs and PNGs at the same quality level.
  • For images requiring transparency, WebP still provided significant advantages over PNG.

This conversion was a game-changer for file size reduction while maintaining high visual fidelity.

Step 3: Inherent Compression through Modern Formats

By converting to WebP using our tools, we inherently benefited from its advanced compression algorithms. Our Image Converter and Image Resizer are designed to output high-quality, optimized images, ensuring that the new WebP files were as small as possible without noticeable quality degradation. We didn't need a separate compression tool; the conversion process itself provided significant byte savings.

Additional Best Practices

Beyond direct image optimization, we also implemented:

  • Lazy Loading: Ensuring images outside the initial viewport only load when they are about to become visible, saving initial bandwidth.
  • Proper width and height Attributes: Adding explicit dimensions to image tags to prevent Cumulative Layout Shift (CLS).

The Results: A Dramatic Improvement

The impact of these focused efforts was immediate and significant. After optimizing images across our target blog sections using our ToolsTol suite, we re-ran our performance tests.

Performance Metrics: Before & After

Metric Before Optimization After Optimization Improvement
Largest Contentful Paint (LCP) 4.8 seconds 1.8 seconds 62.5%
Total Page Size 6.5 MB 2.1 MB 67.7%
Image File Size (per page) 4.5 MB 0.8 MB 82.2%
Google PageSpeed Insights Score (Mobile) 30-40 85-95 Significant

Our LCP improved by a remarkable 62.5%, moving us firmly into the "Good" category for Core Web Vitals. The total page size was slashed by over two-thirds, and the total image payload was reduced by more than 80%.

Tangible Benefits

This dramatic improvement translated directly into a better user experience and stronger SEO performance:

  • Enhanced User Experience: Faster loading times led to reduced bounce rates and increased time on page. Visitors no longer had to wait for content to appear.
  • Improved SEO: Our better Core Web Vitals scores contributed positively to our search engine rankings, increasing organic visibility for our blog posts.
  • Reduced Bandwidth Costs: While seemingly small, the cumulative effect of smaller image files meant less data transferred, leading to lower bandwidth consumption.

Why ToolsTol's Approach Works

Our success in this case study highlights the power and simplicity of our online tools. We designed the Image Resizer and Image Converter with the user in mind:

  • Free and Accessible: All our tools are completely free, requiring no downloads or sign-ups. This makes professional-grade optimization accessible to everyone.
  • Fast and Secure: Our online platform ensures quick processing and secure handling of your images.
  • Quality First: We prioritize maintaining the highest possible image quality while achieving optimal file size reduction.

This case study is a testament to the tangible benefits of proper image optimization and how our accessible, high-quality tools can drive significant performance improvements for any website.

Ready to Optimize Your Site?

Don't let slow-loading images hold your website back. Just like we did, you can achieve remarkable page speed improvements and enhance your Core Web Vitals scores.

Start your optimization journey today:

Improvements Applied:

  1. Heading Hierarchy Adjustment: Changed the final call to action heading from ## Ready to Optimize Your Site? to ### Ready to Optimize Your Site? to maintain a consistent and logical parent-child heading structure within the overall case study. This ensures ### follows ## without jumping a level.