Your PageSpeed Insights score is stuck in the red.
Google's diagnostic keeps flagging the same thing: your Largest Contentful Paint (LCP) is too slow. You've optimized the CSS, you've deferred the JavaScript, and yet that LCP timer refuses to budge past 4 seconds.
Here is the uncomfortable truth most performance guides gloss over: when the LCP element is an image (and according to the HTTP Archive 2025 Web Almanac, it is on 85.3% of desktop pages and 76% of mobile pages), you are not facing a general speed problem.
You are facing a specific image delivery problem. And general CDNs, WordPress caching plugins, and manual compression workflows are built for a different problem altogether.
Most teams that reach this point have already looked at Imgix. It handles format conversion and URL-based transformations competently and has been the default image CDN for SaaS and e-commerce for years.
The issue is what Imgix does not automate: it routes through a single CDN network with no multi-CDN fallback, has no native JavaScript library that detects rendered container width and sizes images to the exact displayed dimensions per device, and its credit-based pricing makes cost forecasting difficult at scale. If LCP is still failing on imgix, the problem almost always lives in one of these three gaps.
For a direct comparison of Gumlet against imgix, Cloudinary, and Cloudflare Images across pricing, format support, and migration effort, see Gumlet's imgix alternatives guide.
An image CDN is the purpose-built solution. Not because it is the trendiest tool in the stack, but because it directly addresses every sub-part of the LCP calculation in a way that a generic CDN simply cannot.
This article breaks down 9 specific, actionable fixes that an image CDN applies to your LCP score, why each one works at a mechanical level, and what you should stop doing right now that is actively making your LCP worse.
This article is for: frontend developers, product engineers, and marketing or growth managers whose pages are failing Core Web Vitals assessments on Google Search Console or PageSpeed Insights and who suspect images are the culprit. No assumptions are made about stack familiarity, whether you are on WordPress, Shopify, a headless CMS, or a custom-built front-end.
Short Answer
Largest Contentful Paint (LCP) measures the time from page navigation to when the largest image or text block renders in the viewport. Google classifies an LCP of 2.5 seconds or less as "good," 2.5 to 4.0 seconds as "needs improvement," and anything above 4.0 seconds as "poor."
Since images are the LCP element on the vast majority of real-world pages, an image CDN directly fixes the core problem: it reduces file size through format conversion and compression, eliminates origin-to-user latency through edge caching, and enables automatic responsive delivery so browsers never download more pixels than they can display.
Combined with correct HTML attributes like fetchpriority="high" and the removal of loading="lazy" from the LCP element, these fixes can bring most image-heavy pages from "poor" into "good" without a full site rebuild.
If you are currently on imgix, the most common gaps that keep LCP from improving despite already using an image CDN are: single-network routing with no automatic CDN fallback, no native JS library that auto-detects rendered container width for responsive sizing, and limited per-image analytics to confirm which optimizations are reaching field data. Fixes 2, 4, and 8 in this article address all three directly.
Key Takeaways
- Images are the LCP element on over 75% of real-world pages, yet 57% of those pages still serve legacy JPEG as the LCP image format, according to the HTTP Archive 2025 Web Almanac.
- An image CDN automates the most impactful fixes: it converts images to WebP or AVIF (reducing file size by 25 to 55% vs JPEG), resizes them to the exact display dimensions, applies perceptually lossless compression, and serves them from the nearest edge node globally.
- Add fetchpriority="high" to the LCP image tag, remove any loading="lazy" attribute from it, and pair that with an image CDN's analytics to confirm which element is actually being measured, and most teams see their LCP score move from "poor" or "needs improvement" into the "good" range within days.
- Gumlet is an image CDN and optimization platform that automates Fixes 1 through 4 and Fix 8 at the infrastructure level, with no re-upload or image migration required.
- Teams currently on imgix typically fail LCP on two specific gaps: imgix uses a single CDN network with no multi-CDN routing, and there is no native library that auto-detects rendered container width for responsive sizing. Switching to Gumlet addresses both without migrating original image files; only a CNAME change is required.
Why Images are the Number One Cause of Poor LCP
Largest Contentful Paint is not a single metric. It is the sum of four sequential sub-parts, each of which can independently cause the total score to fail.
Those four sub-parts are:
- Resource discovery delay: the time from navigation start until the browser finds the LCP resource URL in the page markup.
- Load delay: the time from resource discovery to when the download actually starts.
- Resource load time: the actual download duration, primarily determined by file size and network distance.
- Rendering delay: the time from download completion to when the element is painted on screen.
When the LCP element is an image, all four sub-parts are affected by how that image is stored, formatted, and delivered. A 3 MB uncompressed JPEG served from a single origin server will have a large resource load time on every device, on every network, everywhere in the world.
A lazy-loaded hero image will have a massive discovery delay because the browser cannot prioritize what it has not been told to look for. An image served from a server in Virginia to a user in Singapore will have load delay baked into physics.
The reason image CDN fixes LCP at a structural level is that it intervenes at all four sub-parts simultaneously. For teams already on imgix, a useful diagnostic is what we call the Three-Gap LCP Audit: mapping your LCP sub-part breakdown against the three specific capabilities imgix does not automate: multi-CDN routing (Fix 4), container-aware responsive sizing (Fix 2 and Fix 8), and per-image field analytics (Fix 9).
If your LCP breakdown shows elevated resource load time or load delay, the first two gaps are almost certainly contributing. If you cannot confirm whether optimized formats are reaching real users in field data, the third gap is open.
What an Image CDN Does That a Regular CDN Cannot
A regular CDN caches your files at edge nodes worldwide and serves them from the location closest to the requesting user. It reduces Time to First Byte (TTFB) and eliminates the round-trip to your origin server for cached assets.
That is genuinely useful, and it is worth having. But a regular CDN serves your images exactly as they exist in your origin storage. If that JPEG is 2.4 MB, the user gets a 2.4 MB file, just delivered faster.
An image CDN processes the image before delivery. It reads the browser's Accept header, determines which modern format the browser supports, resizes the image to the correct dimensions for the device and layout, applies compression, and serves the smallest acceptable version.
The result is not just the same file delivered faster. It is a fundamentally smaller, better-suited file delivered from the nearest edge node.
This distinction applies within the image CDN category itself. Imgix processes images on-demand and delivers them through a single CDN network. When that network's nearest node for a given region is degraded, there is no automatic fallback; the request degrades with it. Gumlet routes across multiple CDN providers, selecting the best available edge node per request.
For product pages serving users across multiple regions simultaneously, this difference surfaces directly in TTFB.
Gumlet is an image CDN and optimization platform that connects to your existing image storage (S3, GCS, or a web origin) and handles optimization and delivery automatically, without migrating your original files. It focuses specifically on reducing image payload and improving Core Web Vitals, with per-image analytics to verify the impact on real-user LCP. Teams who want to measure current image payload before making any infrastructure change can run their pages through Gumlet's Website Analyzer.
The 9 Ways an Image CDN Fixes LCP Directly
Each fix below targets a specific part of the LCP chain: resource discovery, download priority, file size, network distance, or a combination of all of them. Some are handled entirely at the infrastructure level by the image CDN, requiring zero code changes.
Others are one-line HTML attribute changes that take under a minute to implement. Together, they address every sub-part of the LCP calculation in a way that no single plugin, server upgrade, or compression script can replicate on its own.
Fix 1: Convert Your Images to WebP or AVIF Automatically
Format conversion is the highest single-lever fix for resource load time, and it is the fix that requires the most effort to implement manually and the least effort when an image CDN handles it.
The numbers behind this fix come from independent format research and Google's own format benchmarks. WebP delivers approximately 25 to 35% smaller files than JPEG at equivalent visual quality. AVIF, which uses AV1-based compression, delivers approximately 45 to 55% smaller files than JPEG at equivalent quality.
On a page where the LCP image is a 600 KB product hero shot in JPEG, converting to WebP brings it to roughly 400 KB. Converting to AVIF brings it to roughly 300 KB. That reduction alone moves the resource load time sub-part substantially.
The challenge with manual format conversion is negotiation: not all browsers support AVIF, and fallbacks have to be managed explicitly in HTML with <picture> elements and <source> tags. An image CDN handles this automatically. It reads the browser's Accept header on every request, serves AVIF to browsers that support it, falls back to WebP for browsers that support WebP but not AVIF, and delivers the original format for everything else. Zero markup changes are required.
Despite this being the most impactful format fix available, the HTTP Archive 2025 Web Almanac data shows that AVIF is still used for only 2% of LCP images. WebP sits at 11%. The remaining 83% of LCP images are still being served as JPEG or PNG, formats designed decades before mobile networks and Core Web Vitals existed.
For a detailed breakdown of when to prefer WebP over AVIF and what the decode speed trade-offs mean for hero images, see Gumlet's AVIF vs WebP comparison.
Fix 2: Resize Images to the Exact Dimensions They Display At
A common source of page weight that rarely shows up in format discussions is the dimension mismatch between the image as stored and the image as displayed.
Serving a 2,400px-wide image in a 400px container wastes 6x the bytes for zero visual benefit. The browser downloads the full file, decodes the full resolution, and then CSS shrinks it visually. The damage to resource load time has already happened.
This problem is pervasive. According to Google's PageSpeed Insights audit data, "properly sized images" is one of the most common audit failures across the web, generating potential savings in the hundreds of kilobytes on a typical e-commerce product page.
An image CDN solves this at the infrastructure level. It generates correctly sized variants on-the-fly via URL parameters. For example, appending ?w=400 to a Gumlet image URL serves a 400px-wide version regardless of the original file's dimensions.
Gumlet's JavaScript integration takes this further: Gumlet.js automatically detects the rendered container width and the device's pixel ratio (DPR) at page load, adds the correct width parameter to image URLs, and delivers the precisely right variant for every device. This process completes in under 30 milliseconds and requires no per-image configuration.
Fix 3: Apply Intelligent Compression Without Sacrificing Visual Quality
Format conversion and resizing reduce the image to the right container and codec. Compression then removes redundant data within that file to reduce it further, and this is where the difference between manual workflows and automated image CDN delivery becomes significant.
Manual compression typically uses a fixed quality parameter. A developer sets quality to 80 in Photoshop or ImageMagick and exports. The problem is that a quality of 80 is not calibrated to what the human eye can actually perceive in any given image. A flat-color illustration at quality 80 is massively over-compressed. A high-detail photograph at quality 80 may still be visually degraded.
Perceptually lossless compression solves this by using a machine learning model to determine the maximum compression level at which no visible quality change occurs, per image. The result is images that look identical to the original but are substantially smaller. This is the compression model Gumlet uses, and it means the platform reduces image payload on average by more than 40% compared to unoptimized origins without any visible quality degradation.
To understand how different compression approaches affect file sizes and visual quality, Gumlet's guide on types of image compression covers the technical trade-offs in detail.
Fix 4: Serve the LCP Image From the Nearest Edge Node
Even a perfectly optimized 80 KB WebP file will fail an LCP target if it has to travel 180 ms across a transatlantic network connection before the first byte arrives.
Network latency is a physical constraint, not a code problem. The only way to fix it is to move the file closer to the user.
A CDN with geographically distributed edge nodes reduces this distance by caching images at Points of Presence (PoPs) close to where users actually are. A request from Singapore that would otherwise round-trip to a U.S.-based origin server is served instead from a Singapore or Hong Kong edge node, with TTFB measured in single-digit milliseconds rather than hundreds.
The distinction between a single CDN and a multi CDN architecture matters here. A provider with one global CDN network delivers from that network's nearest node, which may or may not be optimal for all regions.
Gumlet routes requests across multiple premium CDN providers, including Fastly and CloudFront, selecting the best available edge node per request. This improves resilience (if one network's node in a region is degraded, the request falls to the next) and typically raises cache hit rates during traffic spikes, which is when LCP failures tend to cluster for high-traffic product pages.
This is also the fix where CDN-level image analytics become strategically valuable. Knowing which images have low cache hit rates, which regions are seeing elevated TTFB, and whether the optimized format is being served correctly requires per-image observability, not just aggregate CDN logs.
Explore how Gumlet's image optimization pipeline works across format conversion, compression, and global edge delivery.
Fix 5: Preload the LCP Image to Eliminate Discovery Delay
Resource discovery delay is arguably the most underappreciated LCP sub-part. If the browser does not know an image exists until late in the parsing sequence, it cannot begin fetching it early, regardless of how small or well-formatted the file is.
The fix is a <link rel="preload" as="image"> tag in the document <head>, which tells the browser's preload scanner to discover and begin fetching the LCP resource before the rest of the page has finished parsing.
html
<link rel="preload" as="image" href="/images/hero.webp" fetchpriority="high">
This is especially critical for hero images loaded as CSS background-image properties. CSS backgrounds are invisible to the browser's preload scanner entirely. The browser cannot discover a CSS background-image URL until the stylesheet has been downloaded, parsed, and the matching CSS rule has been applied to a DOM element.
For these images, a preload hint in the <head> is the only reliable way to eliminate discovery delay.
According to the HTTP Archive 2024 HTTP chapter, only about 1.3% of pages with an img-based LCP element actually preload it. Given that resource discovery delay is one of the two most impactful sub-parts of LCP on content-heavy pages, this represents a significant missed opportunity across the web.
Fix 6: Add a Fetchpriority Hint so the Browser Loads the Right Image First
Even when the LCP image is statically discoverable in the HTML, it may not be downloaded first. Browsers maintain a prioritization queue for all resources discovered during page load.
CSS and render-blocking scripts sit at the top. Images are typically assigned low or medium priority by default, meaning a large LCP hero image competes with dozens of other assets.
The fetchpriority="high" attribute directly promotes the LCP image in this queue:
html
<img
src="hero.webp"
fetchpriority="high"
alt="Product hero image"
width="1200"
height="630"
>
In the HTTP Archive 2024 dataset, only 5.6% of desktop pages with an <img> LCP element had fetchpriority=high applied to it. This figure is improving (it was under 0.1% in 2022 before WordPress 6.3 adopted the attribute by default), but it remains absent on the vast majority of pages where it would directly improve LCP.
A practical note: fetchpriority="high" should be applied to the LCP image only. Adding it to multiple images defeats the purpose, as it widens the priority window rather than narrowing it.
Fix 7: Stop Lazy Loading Your LCP Image
This fix is not about adding something. It is about removing something that is almost certainly in your codebase right now, actively making your LCP score worse.
The loading="lazy" attribute is a powerful performance tool for below-the-fold images. It tells the browser to defer fetching an image until the user scrolls it into view, saving bandwidth on images the user may never see. This is genuinely good practice when applied correctly.
The problem is when it is applied to the LCP image. According to the HTTP Archive 2024 Web Almanac, 9.5% of mobile websites are natively lazy loading their LCP image with loading="lazy". Another 6.7% are using JavaScript-based lazy loading on the LCP element. That is roughly 16% of mobile pages actively telling the browser to delay downloading the image that determines their Core Web Vitals score.
If your LCP image has loading="lazy" on it, remove it immediately. The fix takes 30 seconds and typically produces the largest single-session improvement in LCP of any change in this list, because the browser stops artificially deferring the one resource it needs most urgently.
Lazy loading belongs on images below the fold: product thumbnails, gallery images, user-generated content feeds, and similar assets that are not visible on initial page load. The hero image, the product feature banner, the blog post's featured image, the homepage above-the-fold visual: none of these should ever carry loading="lazy".
Fix 8: Use Responsive Delivery to Serve the Right Size for Every Screen
Responsive delivery is the systematic version of Fix 2. Where Fix 2 addresses the concept of dimension mismatch, Fix 8 is about making responsive sizing work automatically across every device, breakpoint, and pixel density ratio.
The HTML mechanism for responsive images is the srcset attribute combined with sizes. The srcset attribute defines a list of available image variants at different widths. The sizes attribute tells the browser how wide the image will actually be rendered at each viewport breakpoint. The browser then selects the most appropriate variant, taking into account both viewport width and device pixel ratio.
html
<img
srcset="hero-400.webp 400w, hero-800.webp 800w, hero-1200.webp 1200w"
sizes="(max-width: 600px) 100vw, 800px"
src="hero-800.webp"
fetchpriority="high"
alt="Hero image"
>
The challenge is maintaining the image variants. A manual workflow requires exporting separate files for each size, naming them correctly, keeping them updated when the source image changes, and writing the srcset markup by hand.
An image CDN generates every variant on-demand from a single source file. When a request arrives, the CDN reads the w= parameter (set automatically by Gumlet.js based on the rendered container width), generates the variant if it has not been cached yet, caches it for subsequent requests, and delivers it.
This eliminates the "oversized images" PageSpeed Insights flag, which is one of the most common audit warnings on image-heavy product and marketing pages.
Fix 9: Use Image Analytics to Confirm What is Actually Being Measured as Your LCP Element
Every fix in this list assumes you are optimizing the correct image. That assumption fails more often than expected.
LCP element determination is not always obvious. Google's algorithm selects the largest element rendered within the initial viewport at the time of load. On a product page with a standard layout, this is usually the main product image.
But on pages with dynamic content, carousels, A/B tested layouts, large promotional banners, or above-the-fold text blocks, the LCP element changes depending on the page variant, the device, and sometimes the user's scroll position at the point Google measures it.
Optimizing the wrong image is a complete waste of effort. A team that compresses their product thumbnail while the actual LCP element is the brand logo in the navigation header will see no LCP improvement, no matter how aggressive the optimization.
To identify the LCP element accurately, use Chrome DevTools (Performance panel, run a trace, look for the "LCP" marker and the associated element in the Insights sidebar) or PageSpeed Insights (the "Diagnose performance issues" section shows the LCP element directly with a screenshot).
For field data that reflects what real users are experiencing rather than what a lab test captures, use CrUX (Chrome User Experience Report) data available in Google Search Console or PageSpeed Insights' "Discover what your real users are experiencing" panel.
Once you have confirmed the LCP element, image-level delivery analytics confirm whether your CDN-side optimization is translating into real-world improvement. Metrics to track: format served per request (is AVIF actually being delivered to supporting browsers?), cache hit rate per image, and average response time by region.
How Image CDN Providers Compare on LCP-Relevant Features
If you are evaluating which image CDN to use, the table below compares the most relevant features from an LCP optimization perspective. Gumlet, Imgix, ImageKit, Cloudflare Images, and Cloudinary are the most commonly considered options for teams focused on Core Web Vitals.
| Feature | Gumlet | Imgix | ImageKit | Cloudflare Images | Cloudinary |
|---|---|---|---|---|---|
| Automatic WebP/AVIF serving | Yes | Yes | Yes | Yes | Yes |
| Multi-CDN delivery | Yes (Fastly + CloudFront) | No (single CDN) | No (single CDN) | No (single network) | No (single CDN) |
| Perceptually lossless ML compression | Yes | Partial | Partial | No | Partial |
| Image-specific LCP analytics | Yes | Limited | Yes | No | Limited |
| Origin flexibility (S3, GCS, web) | Yes | Yes | Yes | No (own storage) | Yes |
| Responsive delivery via JS library | Yes (Gumlet.js) | No native | Yes (IKjs) | No | No native |
| Pricing model | Bandwidth-based | Credit-based | Bandwidth-based | Per-image/transform | Credit-based |
| Imgix migration guide | Yes | No | No | No | No |
A few notes on the comparison. Cloudflare Images requires you to upload images to Cloudflare's own storage, meaning your images live in a proprietary system rather than your existing S3 or GCS bucket.
Imgix and Cloudinary both use credit-based pricing models that can be difficult to predict at scale, particularly for teams running high-variant image pipelines. Gumlet's bandwidth-based model tracks more linearly with actual traffic, which makes cost forecasting straightforward.
On G2, Gumlet has a 4.7 out of 5 rating based on user reviews, with reviewers citing the clean dashboard, CDN delivery speed, and the fact that optimization runs automatically in the background without requiring ongoing developer attention. On Capterra, it holds a 4.9 out of 5 rating across 202 verified reviews, with teams noting the ease of integration compared to building a custom image pipeline.
Should You Switch From Imgix to Gumlet?
If imgix is your current stack and LCP is the primary concern, the three fixes most likely to move your score that imgix does not handle automatically are Fix 4 (multi-CDN routing), Fix 8 (Gumlet.js container-aware responsive sizing), and Fix 3 (perceptual ML compression versus imgix's partial implementation).
None of these require migrating original image files. Gumlet connects to your existing S3, GCS, or web origin and begins serving optimized images through your current URLs after a single CNAME change.
Imgix URL parameters map directly to Gumlet equivalents, and unsupported parameters are discarded cleanly rather than breaking output. The full parameter mapping and migration checklist is documented in Gumlet's imgix migration guide.
The pattern holds across image-heavy platforms. Simplotel, which powers booking websites for 3,000+ hotels across 26 countries, migrated its image pipeline to Gumlet and saw a 97% reduction in image file size compared to original files and 36% better compression than their previous provider.
According to Simplotel's CEO Tarun Goyal, the result was "an immediate improvement in our clients' web vital scores," which translated to a 16% average increase in traffic within the first 60 days. The migration required no code changes and completed with zero downtime.
Putting the 9 Fixes Together: What an Image CDN Handles Automatically
To make implementation straightforward, here is a clear map of which fixes an image CDN handles at the infrastructure level and which requires a one-time code change.
| Fix | Handled By | Effort Required |
|---|---|---|
| Fix 1: WebP/AVIF format conversion | Image CDN (automatic) | Zero (CDN reads Accept header) |
| Fix 2: Dimension-matched resizing | Image CDN + Gumlet.js | Low (add one JS script tag) |
| Fix 3: Intelligent compression | Image CDN (automatic) | Zero |
| Fix 4: Edge delivery from nearest PoP | Image CDN (automatic) | Zero |
| Fix 5: LCP image preload hint | Developer (HTML) | Low (add one link tag to head) |
| Fix 6: fetchpriority="high" | Developer (HTML) | Low (add one attribute to img tag) |
| Fix 7: Remove loading="lazy" from LCP image | Developer (HTML) | Low (remove one attribute) |
| Fix 8: Responsive delivery with srcset | Image CDN + Gumlet.js | Low (Gumlet.js handles variant generation) |
| Fix 9: Image analytics and LCP confirmation | Image CDN analytics + DevTools | Ongoing (monitoring) |
Fixes 5, 6, and 7 are HTML attribute decisions that live in your codebase. Gumlet's integration documentation covers these alongside the CDN setup so that both the infrastructure fixes and the markup fixes are addressed in the same workflow.
The Gumlet image optimization platform includes a free plan for teams who want to connect a staging origin and measure the before-and-after impact on LCP and image payload before committing to a full migration.
See Gumlet's image CDN pricing plans to find the right tier for your traffic volume, or schedule a demo if you want to walk through the setup with a Gumlet engineer.
Frequently Asked Questions
1. What is a good LCP score?
A good LCP score is 2.5 seconds or less, measured at the 75th percentile of real page views as reported by the Chrome User Experience Report (CrUX). Google classifies scores between 2.5 and 4.0 seconds as "needs improvement" and anything above 4.0 seconds as "poor." LCP is one of the three Core Web Vitals metrics and is a direct input into Google's page experience ranking signal, making it the single highest-priority performance metric for most content and e-commerce sites.
2. Does an image CDN actually improve LCP on product pages?
Yes. On product pages, the LCP element is almost always the main product image. An image CDN reduces the resource load time sub-part of LCP by converting the image to a smaller format, applying compression, and serving it from the nearest edge node.
For teams migrating from unoptimized self-hosted images or a basic generic CDN, LCP improvements of 30 to 60% are common within the first week of connecting an image CDN, particularly on mobile where both network speed and device processing constraints amplify the impact of oversized images.
3. What is the difference between WebP and AVIF for LCP performance?
Both are next-gen formats that produce smaller files than JPEG at equivalent visual quality. AVIF achieves higher compression (roughly 45 to 55% smaller than JPEG) but requires more CPU time to decode, which can slow the rendering delay sub-part of LCP on lower-powered mobile devices.
WebP is faster to decode and has near-universal browser support, making it the safer default for hero images. An image CDN like Gumlet serves AVIF to browsers that support it and falls back to WebP or the original format, automatically, without any markup changes required from the developer.
4. Why is my LCP image lazy-loading itself?
It is almost certainly because loading="lazy" has been applied globally to all images on the page, either through a WordPress plugin, a blanket img { loading: lazy } CSS rule, or a JavaScript library that adds lazy loading to all detected images. This is a common anti-pattern.
Lazy loading the LCP element explicitly instructs the browser to delay fetching it, which directly inflates the resource discovery and load delay sub-parts of LCP. Remove loading="lazy" from any image in the initial viewport. Apply it only to images below the fold.
5. How do I find out which image is my LCP element?
Open Chrome DevTools, go to the Performance panel, click Record, reload the page, and stop the recording. In the Insights panel on the right, look for the LCP entry. The associated element is highlighted with a green border in the page preview. Alternatively, run PageSpeed Insights on the target URL and look for the LCP element screenshot in the "Diagnose performance issues" section. For field data from real users across many devices and connections, Google Search Console's Core Web Vitals report surfaces LCP data at the page group level.
6. Does Gumlet fully replace imgix for LCP optimization?
Yes, with a single CNAME change. Gumlet is API-compatible with Imgix. The URL parameter structure maps directly, so existing imgix-formatted URLs continue to resolve without code changes on your end.
The capability differences relevant to LCP are: Gumlet routes requests across multiple CDN providers (Fastly and CloudFront) rather than a single network, includes Gumlet.js which automatically detects rendered container width and serves the correct image variant per device without requiring srcset markup changes, and provides per-image analytics that confirm whether the optimized format is reaching real users.Imgix does not offer native equivalents of these three features. A full parameter mapping and migration guide is available at gumlet.com/imgix-alternative.
Better LCP Starts With Better Image Delivery
LCP failures on image-heavy pages are among the most consistently fixable performance problems on the web.
The root causes are well understood, the fixes are specific and implementable, and most of the heavy lifting happens at the infrastructure level once an image CDN is in the delivery path. The HTML-level fixes (Fixes 5, 6, and 7) each require changing a single line of markup. The infrastructure fixes happen automatically, invisibly, on every request.
The only version of this problem that stays unsolved is the one where you keep optimizing the wrong things: compressing your logo, deferring JavaScript that has nothing to do with image delivery, or upgrading your server tier when your origin is the last place the request actually spends time.
Use the 9 fixes in this article as a checklist. Start with Fixes 7, 6, and 1 in that order (the highest-yield, lowest-effort changes), and connect an image CDN to automate everything else.
If you want to see the impact on your actual pages before changing anything in production, run your site through Gumlet's free Website Analyzer and get a breakdown of your current image payload, format distribution, and estimated LCP improvement.