<BackgroundPicture />
Similar to the <BackgroundImage />
component, the <BackgroundPicture />
component offers Background Image Optimization. But instead of using the background-image
property, it uses the <picture>
element with z-index
set to -1
to display the background image.
Unlike the <BackgroundImage />
component, the <BackgroundPicture />
supports Lazy Loading, Asynchronous Decoding, the sizes
attribute, and the onload fade-in transition. It doesn’t need any JavaScript too.
The body of the <BackgroundPicture />
component will be used as the content of the container element.
Note: Layouts don’t make sense for background images. So, they aren’t supported by the
<BackgroundPicture />
component.
Code Example
---
import {
BackgroundImage,
ImageSupportDetection,
} from "astro-imagetools/components";
const content = await fetch(import.meta.env.CONTENT_URL).then((r) => r.text());
---
<html>
<head>
<ImageSupportDetection />
</head>
<body>
<BackgroundImage
src="/src/images/landscape.jpg"
artDirectives={[
{
src: "/src/images/portrait.jpg",
media: "(orientation: potrait)",
},
]}
>
<Fragment set:html={content} />
</BackgroundImage>
</body>
</html>
Component Props
Below is the list of props that the <BackgroundPicture />
component accepts. Only the src
prop is required.
src
Type: string
Default: undefined
The path to the source image. If local, the path must be relative to the project root. Remote URLs and Data URIs are also supported.
Code example:
<!-- Local Image -->
<BackgroundPicture
src="/src/images/image.jpg"
alt="A local image"
/>
<!-- Remote URL -->
<BackgroundPicture
src="https://example.com/image.jpg"
alt="A remote image"
/>
<!-- Data URI -->
<BackgroundPicture
src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII="
alt="A base64 encoded image"
/>
SSR Usage
In SSR
mode, if you are using local images, you have to generate assets for them first and then you have to pass the path to the assets to the src
property.
---
import src from "../path/to/source_image.jpg";
---
<BackgroundPicture
src={src}
alt="A local image in SSR mode"
/>
The
raw
query parameter has been used to tell the internal Vite plugin to emit the asset from the source image unchanged.
tag
Type: string
Default: section
Which html tag to use for the html element to apply the generated background image sets to.
Code Example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
tag="section"
/>
sizes
Type: string
or (breakpoints: number[]) => string
Default: (breakpoints) => `(min-width: ${breakpoints[breakpopints.length - 1]}px) ${breakpoints[breakpopints.length - 1]}px, 100vw
A string or function that returns a string suitable for the value of the sizes
attribute of the generated <img />
element. The final calculated breakpoints
are passed to the function as a parameter.
Code example:
<!-- string type -->
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
sizes="(min-width: 1024px) 1024px, 100vw"
/>
<!-- function type -->
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
sizes={(breakpoints) => {
const maxWidth = breakpoints[breakpoints.length - 1];
return `(min-width: ${maxWidth}px) ${maxWidth}px, 100vw`;
}}
/>
preload
Type: "heic" | "heif" | "avif" | "jpg" | "jpeg" | "png" | "tiff" | "webp" | "gif"
Default: undefined
Which format of image set to preload.
Note: It’s not reasonable to preload multiple formats of the same image. And due to the factors like file size and browser support, it’s not possible to pick the best format automatically.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
preload="webp"
/>
loading
Type: "lazy" | "eager" | "auto" | null
Default: preload ? "eager" : "lazy"
The value of the loading
attribute of the generated <img />
element. If null
is provided, the loading
attribute will be omitted.
Code Example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
loading="lazy"
/>
decoding
Type: "async" | "sync" | "auto" | null
Default: "async"
The value of the decoding
attribute of the generated <img />
element. If null
is provided, the decoding
attribute will be omitted.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
decoding="async"
/>
attributes
Type:
declare interface Attributes {
container?: Record<any, any>;
picture?: Record<any, any>;
style?: Record<any, any>;
link?: Omit<Record<any, any>, "as" | "rel" | "imagesizes" | "imagesrcset">;
img?: Omit<
Record<any, any>,
| "src"
| "alt"
| "srcset"
| "sizes"
| "width"
| "height"
| "loading"
| "decoding"
>;
}
Default: {}
The HTML attributes to add to the generate elements. If the class
, style
, and onload
attributes are present, the values passed via this config will be merged.
Code Example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
attributes={{
link: {
fetchpriority: "high"
}
}}
/>
placeholder
Type: "dominantColor" | "blurred" | "tracedSVG" | "none"
Default: "blurred"
The placeholder to be displayed while the image is loading.
If placeholder
is set to "dominantColor"
, the dominant color of the source
image will be used as the placeholder.
If the value is set to "blurred"
, a very low-resolution version of the
provided image will be enlarged and used as the placeholder.
If the value is set to "tracedSVG"
, a traced SVG of the image will be used
as the placeholder. If the value is set to "none"
, no placeholder will be
displayed.
Note: If the value is set to
"tracedSVG"
, the placeholder can be customized to be a Posterized SVG too. See the formatOptions prop for more details.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
placeholder="blurred"
/>
breakpoints
Type: number[] | { count?: number; minWidth?: number; maxWidth?: number }
Default: undefined
An array of widths in pixels to generate image sets for. If not provided, the breakpoints will be calculated automatically.
If an object is passed then the breakpoints will be calculated automatically based
on the values of the count
,
minWidth
, and maxWidth
properties. The count
property is to specify the number
of breakpoints to generate. The minWidth
and maxWidth
properties are to specify
the widths to generate in the range between their values.
When an object is passed or the breakpoints
prop is not provided, the breakpoints
are calculated using a simple formula/algorithm. Instead of explaining the complete
algorithm here, I am linking to the code.
Code example:
<!-- number[] type -->
<BackgroundPicture
src="https://picsum.photos/1600/900"
alt="A random image"
breakpoints={[200, 400, 800, 1600]}
/>
<!-- { count?: number; minWidth?: number; maxWidth?: number } type -->
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
breakpoints={{ count: 3, minWidth: 300, maxWidth: 1024 }}
/* three breakpoints will be generated ranging from 300px to 1024px */
/>
objectFit
Type: "fill" | "contain" | "cover" | "none" | "scale-down"
Default: cover
The value of the object-fit
CSS property of the generated <img />
element.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
objectFit="cover"
/>
objectPosition
Type: string
Default: 50% 50%
The value of the object-position
CSS property of the generated <img />
element.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
objectPosition="50% 50%"
/>
format
Type: format | format[] | [] | null
format
: "heic" | "heif" | "avif" | "jpg" | "jpeg" | "png" | "tiff" | "webp" | "gif"
Default:
["avif", "webp"]
The image format or formats to generate image sets for.
If format
is set to null
or []
, no additional image set will be
generated. > Note: Passing []
or null
does not necessarily mean that
no image sets will be generated. Image sets will still be generated for the
source format if includeSourceFormat
is set to true
(which is the
default value) and for the format specified in the fallbackFormat
prop
(the default value is the source format).
Code Example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
format={["avif", "webp"]}
/>
fallbackFormat
Type: format
Default: The format of the source image
The format the browser will fallback to if the other formats are not supported.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
format={["webp", "jpg"]}
fallbackFormat="png"
/>
includeSourceFormat
Type: boolean
Default: true
Whether to generate image set for the source format or not.
Code example:
<BackgroundPicture
src="/src/images/image.tiff"
alt="A random image"
fallbackFormat="png"
includeSourceFormat={false}
/>
formatOptions
Type
formatOptions
is an object that takes config options for all the supported formats: heic
, heif
, avif
, jpg
, jpeg
, png
, tiff
, webp
, gif
, and tracedSVG
.
The supported config options of all the formats except tracedSVG
are: flip
, flop
, invert
, flatten
, normalize
, grayscale
, hue
, saturation
, brightness
, width
, height
, aspect
, background
, tint
, blur
, median
, rotate
, quality
, fit
, kernel
, position
.
The config options supported by the tracedSVG
format are listed below.
Default: The default values for the all the formats except tracedSVG
are inherited from the direct configs of the {tracedSVG
property, see the PotraceOptions
interface.
The configuration options for the different formats. These configuration options will be respected when generating image sets for different formats.
The tracedSVG
config object is used only when the placeholder
prop is set to "tracedSVG"
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
placeholder="tracedSVG"
format={["webp", "jpg"]}
fallbackFormat="png"
includeSourceFormat={false}
formatOptions={{
jpg: {
quality: 80,
},
png: {
quality: 80,
},
webp: {
quality: 50,
},
tracedSVG: {
options: {
background: "#fff",
color: "#000",
turnPolicy: "black",
turdSize: 1,
alphaMax: 1,
optCurve: true,
threshold: 100,
blackOnWhite: false,
},
},
}}
/>
tracedSVG
All the properties of the tracedSVG
property are the configuration options supported by the node-potrace
library. These options are used to generate traced SVGs when the placeholder
prop is set to "tracedSVG"
. All the properties defined below are optional.
Note: Most of the below jargons are taken from the
potrace
documentation. I have tried my best to simplify the config options and make the documentation as simple and clear as possible.If you want to go deeper into this, check the Technical documentation of the original C
potrace
library.If you have a good knowledge on the
potrace
library and about bitmap tracing and posterizing, please consider contributing to update the documentation of this section.
function
Type: "trace" | "posterize"
Default: "trace"
Which method of the node-potrace
library to use. The posterize
method is basically tracing the image multiple times to produce a more accurate result. See this example for more information.
options
turnPolicy
Type: "black" | "white" | "left" | "right" | "minority" | "majority"
Default: "minority"
How to resolve ambiguities in path decomposition. Refer to the potrace-algorithm documentaion (PDF, page 4) for more information.
turdSize
Type: number
Default: 2
Suppress speckles of up to this size.
alphaMax
Type: number
Default: 1
Corner threshold parameter.
optCurve
Type: boolean
Default: true
Curve optimization.
optTolerance
Type: number
Default: 0.2
Curve optimization tolerance.
threshold
Type: number
Default: -1
When function
is "trace"
:
Threshold below which color is considered black. Should be a number between 0 and 255 or -1
in which case threshold will be selected automatically using Algorithm For Multilevel Thresholding.
When function
is "posterize"
:
Breaks image into foreground and background (and only foreground being broken into desired number of layers). Basically when provided it becomes a threshold for last (least opaque) layer and then steps - 1
intermediate thresholds calculated. If steps is an array of thresholds and every value from the array is lower (or larger if blackOnWhite parameter set to false
) than threshold - threshold will be added to the array, otherwise just ignored.
blackOnWhite
Type: boolean
Default: true
Specifies colors by which side from threshold should be turned into vector shape.
color
Type: "auto" | string
Default: "auto"
Fill color for the traced image. If "auto"
is provided, the color will be black or white depending on the blackOnWhite
property.
background
Type: "transparent" | string
Default: "transparent"
Background color of the traced image. If "transparent"
is provided, no background will be present.
fill
Type: "spread" | "dominant" | "median" | "mean"
Determines how fill color for each layer should be selected.
dominant
- Most frequent color in range (used by default),mean
- Arithmetic mean (average),median
- Median color,spread
- Ignores color information of the image and just spreads colors equally in range between 0 andthreshold
(orthreshold
and ..255 ifblackOnWhite
is set tofalse
).
Note: This option is available only when
function
is"posterize"
.
ranges
Type: "auto" | "equal"
How color stops for each layer should be selected. Ignored if steps
is an array. Possible values are:
auto
- Performs automatic thresholding (using Algorithm For Multilevel Thresholding). Preferable method for already posterized sources, but takes long time to calculate 5 or more thresholds (exponential time complexity) (used by default)equal
- Ignores color information of the image and breaks available color space into equal chunks
Note: This option is available only when
function
is"posterize"
.
steps
Type: number | number[]
Specifies desired number of layers in resulting image. If a number provided - thresholds for each layer will be automatically calculated according to ranges
property. If an array provided it expected to be an array with precomputed thresholds for each layer (in range between 0 and 255).
Note: This option is available only when
function
is"posterize"
.
Code example:
---
const src = "https://picsum.photos/1024/768";
const alt = "A random image";
const placeholder = "tracedSVG";
const traceOptions = {
background: "#fff",
color: "#000",
turnPolicy: "black",
turdSize: 1,
alphaMax: 1,
optCurve: true,
threshold: 100,
blackOnWhite: false,
};
const posterizeOptions = {
fill: "spread",
steps: [0, 50, 100],
ranges: "equal",
};
---
<BackgroundPicture
src={src}
alt={alt}
placeholder={placeholder}
/* tracing SVG */
formatOptions={{
tracedSVG: {
function: "trace",
options: traceOptions,
},
}}
/>
<BackgroundPicture
src={src}
alt={alt}
placeholder={placeholder}
/* posterizing SVG */
formatOptions={{
tracedSVG: {
function: "posterize",
options: {
...traceOptions,
...posterizeOptions,
},
},
}}
/>
fadeInTransition
Type: boolean | { delay?: string; duration?: string; timingFunction?: string; }
Default: true | { delay: "0s"; duration?: "1s"; timingFunction: "ease"; }
Whether or not to fade in the image when it is loaded. If an object is passed with the delay
, duration
, and timingFunction
properties, the values will be used as values for the transition-delay
, transition-duration
, and transition-timing-function
CSS properties, respectively.
Note: This prop is only available when the
placeholder
prop of at least one source is not"none"
.
Code Example:
---
const src = "https://picsum.photos/1024/768";
const alt = "A random image";
---
<!-- boolean type -->
<BackgroundPicture
src={src}
alt={alt}
fadeInTransition={false}
/>
<!-- { delay: string; duration: string; timingFunction: string; } type -->
<BackgroundPicture
src={src}
alt={alt}
fadeInTransition={{
delay: "0.5s",
duration: "0.5s",
timingFunction: "linear",
}}
/>
artDirectives
Type: ArtDirective[]
An ArtDirective
object can take all the props supported by the{” ”}
{preload
, loading
,
decoding
, attributes
, and fadeInTransition
. The only addition is
media
. Only the src
and media
properties are
required.
Default: undefined
The list of art directions to be applied to the generated picture.
Code Example:
<BackgroundPicture
src="/src/images/landscape.jpg"
alt="alt text"
artDirectives={[
{
media: "(max-aspect-ratio: 3/2)",
src: "/src/images/portrait.jpg",
breakpoints: [256, 384, 576],
width: 768,
height: 1024,
format: ["avif"],
fallbackFormat: "webp",
includeSourceFormat: false,
},
]}
/>
media
Type: string
Default: undefined
The CSS media query to use to define the art direction.
Code Example:
<BackgroundPicture
src="/src/image/landscape.jpg"
alt="A landscape image"
rotate={22.5}
artDirectives={[
{
src: "/src/image/dark-potrait.jpg",
media: "(prefers-color-scheme: dark) and (orientation: portrait)",
},
{
src: "/src/image/light-potrait.jpg",
media: "(prefers-color-scheme: light) and (orientation: portrait)",
},
{
src: "/src/image/dark-landscape.jpg",
media: "(prefers-color-scheme: dark) and (orientation: landscape)",
},
]}
/>
flip
Type: boolean
Default: undefined
Flip the image about the vertical axis. This step is always performed after any rotation.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
flip={true}
/>
flop
Type: boolean
Default: undefined
Flop the image about the vertical axis. This step is always performed after any rotation.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
flop={true}
/>
invert
Type: boolean
Default: undefined
Produces a negative of the image.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
invert={true}
/>
flatten
Type: boolean
Default: undefined
Whether to remove the alpha channel of the image or not, reducing filesize. Transparent pixels will be merged with the color set by background
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
flatten={true}
/>
normalize
Type: boolean
Default: undefined
Normalizes the image by stretching its luminance to cover the full dynamic range. This Enhances the output image contrast.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
normalize={true}
/>
grayscale
Type: boolean
Default: undefined
Converts the image to an 8-bit grayscale image.
Note: If
true
the image will be converted to theb-w
colorspace, meaning the resulting image will only have one channel.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
grayscale={true}
/>
hue
Type: number
Default: undefined
Adjusts the images hue
rotation by the given number of degrees. Commonly used together with saturation
and brightness
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
hue={-30}
/>
saturation
Type: number
Default: undefined
Adjusts the images saturation
with the given saturation multiplier. Commonly used together with hue
and brightness
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
saturation={0.5}
/>
brightness
Type: number
Default: undefined
Adjusts the images brightness
with the given brightness multiplier. Commonly used together with hue
and saturation
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
brightness={0.5}
/>
width
| w
Type: number
Default: The width of the source image
Resizes the image to be the specified amount of pixels wide. If not given the height
will be scaled accordingly.
Note: The specified
width
will be used to resize the source image when loading it. The final widths of the image will be based on the final calculatedbreakpoints
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
width={1024}
/>
height
| h
Type: number
Default: The height of the source image
Resizes the image to be the specified amount of pixels tall. If not given the width
will be scaled accordingly.
Note: The specified
height
will be used to resize the source image when loading it. The final heights of the image will be based on the final calculatedbreakpoints
.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
height={300}
/>
aspect
| ar
Type: number
Default: The aspect ratio of the source image
Resizes the image to be the specified aspect ratio. If height
and width
are both provided, this will be ignored. If height
is provided, the height
will be scaled accordingly. If width
is provided, the height will be scaled accordingly. If neither height nor width are provided, the image will be cropped to the given aspect
ratio.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
aspect={1.3333333333333333}
/>
background
Type: string
Default: undefined
This instructs various props (e.g. rotate
) to use the specified color when filling empty spots in the image.
Note: This prop does nothing on it’s own, it has to be used in conjunction with another prop.
Code example:
The below example demonstrates all the posible cases when the background
prop is used.
---
const src = "https://picsum.photos/1024/768";
const alt = "A random image";
---
<BackgroundPicture
src={src}
alt={alt}
flatten={true}
background="#FFFFFFAA"
/>
<BackgroundPicture
src={src}
alt={alt}
rotate={90}
background="hsl(360, 100%, 50%)"
/>
<BackgroundPicture
src={src}
alt={alt}
width={800}
height={450}
fit="contain"
background="crimson"
/>
tint
Type: string
Default: undefined
Tints the image using the provided chroma while preserving the image luminance. If the image has an alpha channel it will be untouched.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
tint="rgba(10,33,127)"
/>
blur
Type: string
Default: undefined
Blurs the image. If the value is true
, it performs a fast blur. When a number
between 0.3
and 1000
is provided, it performs a more accurate gaussian blur.
Code example:
---
const src = "https://picsum.photos/1024/768";
const alt = "A random image";
---
<BackgroundPicture
src={src}
alt={alt}
blur={true}
/* A fast blur will be performed */
/>
<BackgroundPicture
src={src}
alt={alt}
blur={100}
/* A more accurate blur will be performed */
/>
median
Type: number | boolean
Default: undefined
Applies a median filter. This is commonly used to remove noise from images.
Code example:
---
const src = "https://picsum.photos/1024/768";
const alt = "A random image";
---
<!-- boolean type -->
<BackgroundPicture
src={src}
alt={alt}
median={true}
/>
<!-- number type -->
<BackgroundPicture
src={src}
alt={alt}
median={50}
/>
rotate
Type: number
Default: undefined
Rotate the image by the specified number of degrees.
Note: The empty parts are filled with the color specified in the
background
prop.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
rotate={90}
/>
quality
Type: number
Default: undefined
All formats (except gif
) allow the quality to be adjusted by setting this directive.
The argument must be a number between 0
and 100
.
See sharps Output options for default quality values.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
quality={50}
/>
fit
Type: "cover" | "contain" | "fill" | "inside" | "outside"
Default: undefined
When both width
and height
are provided, this directive can be used to specify the method by which the image should fit.
Note: The empty parts are filled with the color specified in the
background
prop.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
width={800}
height={450}
fit="contain"
/>
kernel
Type: "nearest" | "cubic" | "mitchell" | "lanczos2" | "lanczos3"
Default: undefined
The interpolation kernel to use when resizing the images.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
kernel="lanczos3"
/>
position
Type: "top" | "right top" | "right" | "right bottom" | "bottom" | "left bottom" | "left" | "left top" | "north" | "northeast" | "east" | "southeast" | "south" | "southwest" | "west" | "northwest" | "center" | "centre" | "cover" | "entropy" | "attention"
Default: undefined
When both width
and height
are provided AND fit
is is set to cover
or contain
, this directive can be used to set the position of the image.
See
sharp
’s resize options for more information.
Code example:
<BackgroundPicture
src="https://picsum.photos/1024/768"
alt="A random image"
width={800}
height={450}
fit="contain"
position="attention"
/>