The NgOptimizedImage directive makes it easy to adopt performance best practices for loading images.
The directive ensures that the loading of the Largest Contentful Paint (LCP) image is prioritized by:
fetchpriority attribute on the <img> tagsrcset attributeIn addition to optimizing the loading of the LCP image, NgOptimizedImage enforces a number of image best practices, such as:
width and height
width or height have been set incorrectlyimport { NgOptimizedImage } from '@angular/common' The directive is defined as a standalone directive, so components should import it directly.
An image loader is not required in order to use NgOptimizedImage, but using one with an image CDN enables powerful performance features, including automatic srcsets for your images.
A brief guide for setting up a loader can be found in the Configuring an Image Loader section at the end of this page.
To activate the NgOptimizedImage directive, replace your image's src attribute with ngSrc.
<img ngSrc="cat.jpg">
If you're using a built-in third-party loader, make sure to omit the base URL path from src, as that will be prepended automatically by the loader.
priority
Always mark the LCP image on your page as priority to prioritize its loading.
<img ngSrc="cat.jpg" width="400" height="200" priority>
Marking an image as priority applies the following optimizations:
fetchpriority=high (read more about priority hints here)loading=eager (read more about native lazy loading here)Angular displays a warning during development if the LCP element is an image that does not have the priority attribute. A page’s LCP element can vary based on a number of factors - such as the dimensions of a user's screen, so a page may have multiple images that should be marked priority. See CSS for Web Vitals for more details.
In order to prevent image-related layout shifts, NgOptimizedImage requires that you specify a height and width for your image, as follows:
<img ngSrc="cat.jpg" width="400" height="200">
For responsive images (images which you've styled to grow and shrink relative to the viewport), the width and height attributes should be the instrinsic size of the image file.
For fixed size images, the width and height attributes should reflect the desired rendered size of the image. The aspect ratio of these attributes should always match the intrinsic aspect ratio of the image.
Note: If you don't know the size of your images, consider using "fill mode" to inherit the size of the parent container, as described below:
fill modeIn cases where you want to have an image fill a containing element, you can use the fill attribute. This is often useful when you want to achieve a "background image" behavior. It can also be helpful when you don't know the exact width and height of your image, but you do have a parent container with a known size that you'd like to fit your image into (see "object-fit" below).
When you add the fill attribute to your image, you do not need and should not include a width and height, as in this example:
<img ngSrc="cat.jpg" fill>
You can use the object-fit CSS property to change how the image will fill its container. If you style your image with object-fit: "contain", the image will maintain its aspect ratio and be "letterboxed" to fit the element. If you set object-fit: "cover", the element will retain its aspect ratio, fully fill the element, and some content may be "cropped" off.
See visual examples of the above at the MDN object-fit documentation.
You can also style your image with the object-position property to adjust its position within its containing element.
Important note: For the "fill" image to render properly, its parent element must be styled with position: "relative", position: "fixed", or position: "absolute".
Depending on the image's styling, adding width and height attributes may cause the image to render differently. NgOptimizedImage warns you if your image styling renders the image at a distorted aspect ratio.
You can typically fix this by adding height: auto or width: auto to your image styles. For more information, see the web.dev article on the <img> tag.
If the height and width attribute on the image are preventing you from sizing the image the way you want with CSS, consider using "fill" mode instead, and styling the image's parent element.
NgOptimizedImage includes a number of features designed to improve loading performance in your app. These features are described in this section.
You can add a preconnect resource hint for your image origin to ensure that the LCP image loads as quickly as possible. Always put resource hints in the <head> of the document.
<link rel="preconnect" href="https://my.cdn.origin" />
By default, if you use a loader for a third-party image service, the NgOptimizedImage directive will warn during development if it detects that there is no preconnect resource hint for the origin that serves the LCP image.
To disable these warnings, inject the PRECONNECT_CHECK_BLOCKLIST token:
providers: [
{provide: PRECONNECT_CHECK_BLOCKLIST, useValue: 'https://your-domain.com'}
], srcset
Defining a srcset attribute ensures that the browser requests an image at the right size for your user's viewport, so it doesn't waste time downloading an image that's too large. NgOptimizedImage generates an appropriate srcset for the image, based on the presence and value of the sizes attribute on the image tag.
If your image should be "fixed" in size (i.e. the same size across devices, except for pixel density), there is no need to set a sizes attribute. A srcset can be generated automatically from the image's width and height attributes with no further input required.
Example srcset generated: <img ... srcset="image-400w.jpg 1x, image-800w.jpg 2x">
If your image should be responsive (i.e. grow and shrink according to viewport size), then you will need to define a sizes attribute to generate the srcset.
If you haven't used sizes before, a good place to start is to set it based on viewport width. For example, if your CSS causes the image to fill 100% of viewport width, set sizes to 100vw and the browser will select the image in the srcset that is closest to the viewport width (after accounting for pixel density). If your image is only likely to take up half the screen (ex: in a sidebar), set sizes to 50vw to ensure the browser selects a smaller image. And so on.
If you find that the above does not cover your desired image behavior, see the documentation on advanced sizes values.
By default, the responsive breakpoints are:
[16, 32, 48, 64, 96, 128, 256, 384, 640, 750, 828, 1080, 1200, 1920, 2048, 3840]
If you would like to customize these breakpoints, you can do so using the IMAGE_CONFIG provider:
providers: [
{
provide: IMAGE_CONFIG,
useValue: {
breakpoints: [16, 48, 96, 128, 384, 640, 750, 828, 1080, 1200, 1920]
}
},
], If you would like to manually define a srcset attribute, you can provide your own using the ngSrcset attribute:
<img ngSrc="hero.jpg" ngSrcset="100w, 200w, 300w">
If the ngSrcset attribute is present, NgOptimizedImage generates and sets the srcset based on the sizes included. Do not include image file names in ngSrcset - the directive infers this information from ngSrc. The directive supports both width descriptors (e.g. 100w) and density descriptors (e.g. 1x).
<img ngSrc="hero.jpg" ngSrcset="100w, 200w, 300w" sizes="50vw">
To disable srcset generation for a single image, you can add the disableOptimizedSrcset attribute on the image:
<img ngSrc="about.jpg" disableOptimizedSrcset>
By default, NgOptimizedImage sets loading=lazy for all images that are not marked priority. You can disable this behavior for non-priority images by setting the loading attribute. This attribute accepts values: eager, auto, and lazy. See the documentation for the standard image loading attribute for details.
<img ngSrc="cat.jpg" width="400" height="200" loading="eager">
You may want to have images displayed at varying widths on differently-sized screens. A common example of this pattern is a grid- or column-based layout that renders a single column on mobile devices, and two columns on larger devices. You can capture this behavior in the sizes attribute, using a "media query" syntax, such as the following:
<img ngSrc="cat.jpg" width="400" height="200" sizes="(max-width: 768px) 100vw, 50vw">
The sizes attribute in the above example says "I expect this image to be 100 percent of the screen width on devices under 768px wide. Otherwise, I expect it to be 50 percent of the screen width.
For additional information about the sizes attribute, see web.dev or mdn.
NgOptimizedImage
A "loader" is a function that generates an image transformation URL for a given image file. When appropriate, NgOptimizedImage sets the size, format, and image quality transformations for an image.
NgOptimizedImage provides both a generic loader that applies no transformations, as well as loaders for various third-party image services. It also supports writing your own custom loader.
| Loader type | Behavior |
|---|---|
| Generic loader | The URL returned by the generic loader will always match the value of src. In other words, this loader applies no transformations. Sites that use Angular to serve images are the primary intended use case for this loader. |
| Loaders for third-party image services | The URL returned by the loaders for third-party image services will follow API conventions used by that particular image service. |
| Custom loaders | A custom loader's behavior is defined by its developer. You should use a custom loader if your image service isn't supported by the loaders that come preconfigured with NgOptimizedImage. |
Based on the image services commonly used with Angular applications, NgOptimizedImage provides loaders preconfigured to work with the following image services:
| Image Service | Angular API | Documentation |
|---|---|---|
| Cloudflare Image Resizing | provideCloudflareLoader | Documentation |
| Cloudinary | provideCloudinaryLoader | Documentation |
| ImageKit | provideImageKitLoader | Documentation |
| Imgix | provideImgixLoader | Documentation |
To use the generic loader no additional code changes are necessary. This is the default behavior.
To use an existing loader for a third-party image service, add the provider factory for your chosen service to the providers array. In the example below, the Imgix loader is used:
providers: [
provideImgixLoader('https://my.base.url/'),
], The base URL for your image assets should be passed to the provider factory as an argument. For most sites, this base URL should match one of the following patterns:
You can learn more about the base URL structure in the docs of a corresponding CDN provider.
To use a custom loader, provide your loader function as a value for the IMAGE_LOADER DI token. In the example below, the custom loader function returns a URL starting with https://example.com that includes src and width as URL parameters.
providers: [
{
provide: IMAGE_LOADER,
useValue: (config: ImageLoaderConfig) => {
return `https://example.com/images?src=${config.src}&width=${config.width}`;
},
},
], A loader function for the NgOptimizedImage directive takes an object with the ImageLoaderConfig type (from @angular/common) as its argument and returns the absolute URL of the image asset. The ImageLoaderConfig object contains the src property, and optional width and loaderParams properties.
Note: even though the width property may not always be present, a custom loader must use it to support requesting images at various widths in order for ngSrcset to work properly.
loaderParams PropertyThere is an additional attribute supported by the NgOptimizedImage directive, called loaderParams, which is specifically designed to support the use of custom loaders. The loaderParams attribute take an object with any properties as a value, and does not do anything on its own. The data in loaderParams is added to the ImageLoaderConfig object passed to your custom loader, and can be used to control the behavior of the loader.
A common use for loaderParams is controlling advanced image CDN features.
The following shows an example of a custom loader function. This example function concatenates src and width, and uses loaderParams to control a custom CDN feature for rounded corners:
const myCustomLoader = (config: ImageLoaderConfig) => {
let url = `https://example.com/images/${config.src}?`;
let queryParams = [];
if (config.width) {
queryParams.push(`w=${config.width}`);
}
if (config.loaderParams?.roundedCorners) {
queryParams.push('mask=corners&corner-radius=5');
}
return url + queryParams.join('&');
}; Note that in the above example, we've invented the 'roundedCorners' property name to control a feature of our custom loader. We could then use this feature when creating an image, as follows:
<img ngSrc="profile.jpg" width="300" height="300" [loaderParams]="{roundedCorners: true}">
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https://angular.io/guide/image-directive