JavaScript Load Image
A JavaScript library to load and transform image files.
Contents
Demo
Description
JavaScript Load Image is a library to load images provided as File or Blob objects or via URL. It returns an optionally scaled and/or cropped HTML img or canvas element. It also provides methods to parse image meta data to extract IPTC and Exif tags as well as embedded thumbnail images and to restore the complete image header after resizing.
Setup
Include the (combined and minified) JavaScript Load Image script in your HTML markup:
<script src="js/load-image.all.min.js"></script>
Or alternatively, choose which components you want to include:
<script src="js/load-image.js"></script>
<script src="js/load-image-scale.js"></script>
<script src="js/load-image-meta.js"></script>
<script src="js/load-image-fetch.js"></script>
<script src="js/load-image-orientation.js"></script>
<script src="js/load-image-exif.js"></script>
<script src="js/load-image-exif-map.js"></script>
<script src="js/load-image-iptc.js"></script>
<script src="js/load-image-iptc-map.js"></script>
Usage
Image loading
In your application code, use the loadImage() function like this:
document.getElementById('file-input').onchange = function (e) {
loadImage(
e.target.files[0],
function (img) {
document.body.appendChild(img)
},
{ maxWidth: 600 } // Options
)
}
Image scaling
It is also possible to use the image scaling functionality with an existing image:
var scaledImage = loadImage.scale(
img, // img or canvas element
{ maxWidth: 600 }
)
Requirements
The JavaScript Load Image library has zero dependencies.
However, JavaScript Load Image is a very suitable complement to the Canvas to Blob library.
API
The loadImage() function accepts a
File or
Blob object or a simple image URL
(e.g. 'https://example.org/image.png') as first argument.
If a File or
Blob is passed as parameter, it
returns a HTML img element if the browser supports the
URL API or a
FileReader object if
supported, or false.
It always returns a HTML
img element when
passing an image URL:
document.getElementById('file-input').onchange = function (e) {
var loadingImage = loadImage(
e.target.files[0],
function (img) {
document.body.appendChild(img)
},
{ maxWidth: 600 }
)
if (!loadingImage) {
// Alternative code ...
}
}
The img element or
FileReader object returned by
the loadImage() function allows to abort the loading process by setting the
onload and onerror event handlers to null:
document.getElementById('file-input').onchange = function (e) {
var loadingImage = loadImage(
e.target.files[0],
function (img) {
document.body.appendChild(img)
},
{ maxWidth: 600 }
)
loadingImage.onload = loadingImage.onerror = null
}
The second argument must be a callback function, which is called when the
image has been loaded or an error occurred while loading the image. The callback
function is passed two arguments.
The first is either an HTML img element, a
canvas element, or an
Event object of type error.
The second is on object with the original image dimensions as properties and
potentially additional meta data:
var imageUrl = 'https://example.org/image.png'
loadImage(
imageUrl,
function (img, data) {
if (img.type === 'error') {
console.error('Error loading image ' + imageUrl)
} else {
document.body.appendChild(img)
console.log('Original image width: ', data.originalWidth)
console.log('Original image height: ', data.originalHeight)
}
},
{ maxWidth: 600 }
)
Options
The optional third argument to loadImage() is a map of options.
They can be used the following way:
loadImage(
fileOrBlobOrUrl,
function (img) {
document.body.appendChild(img)
},
{
maxWidth: 600,
maxHeight: 300,
minWidth: 100,
minHeight: 50,
canvas: true
}
)
All settings are optional. By default, the image is returned as HTML img
element without any image size restrictions.
maxWidth
Defines the maximum width of the img/canvas element.
maxHeight
Defines the maximum height of the img/canvas element.
minWidth
Defines the minimum width of the img/canvas element.
minHeight
Defines the minimum height of the img/canvas element.
sourceWidth
The width of the sub-rectangle of the source image to draw into the destination
canvas.
Defaults to the source image width and requires canvas: true.
sourceHeight
The height of the sub-rectangle of the source image to draw into the destination
canvas.
Defaults to the source image height and requires canvas: true.
top
The top margin of the sub-rectangle of the source image.
Defaults to 0 and requires canvas: true.
right
The right margin of the sub-rectangle of the source image.
Defaults to 0 and requires canvas: true.
bottom
The bottom margin of the sub-rectangle of the source image.
Defaults to 0 and requires canvas: true.
left
The left margin of the sub-rectangle of the source image.
Defaults to 0 and requires canvas: true.
contain
Scales the image up/down to contain it in the max dimensions if set to true.
This emulates the CSS feature background-image: contain.
cover
Scales the image up/down to cover the max dimensions with the image dimensions
if set to true.
This emulates the CSS feature background-image: cover.
aspectRatio
Crops the image to the given aspect ratio (e.g. 16/9).
Setting the aspectRatio also enables the crop option.
pixelRatio
Defines the ratio of the canvas pixels to the physical image pixels on the
screen.
Should be set to window.devicePixelRatio unless the scaled image is not rendered
on screen.
Defaults to 1 and requires canvas: true.
downsamplingRatio
Defines the ratio in which the image is downsampled.
By default, images are downsampled in one step. With a ratio of 0.5, each step
scales the image to half the size, before reaching the target dimensions.
Requires canvas: true.
imageSmoothingEnabled
If set to false,
disables image smoothing.
Defaults to true and requires canvas: true.
imageSmoothingQuality
Sets the
quality of image smoothing.
Possible values: 'low', 'medium', 'high'
Defaults to 'low' and requires canvas: true.
crop
Crops the image to the maxWidth/maxHeight constraints if set to true.
Enabling the crop option also enables the canvas option.
orientation
Transform the canvas according to the specified Exif orientation, which can be
an integer in the range of 1 to 8 or the boolean value true.
When set to true, it will set the orientation value based on the EXIF data of
the image, which will be parsed automatically if the exif library is available.
Setting orientation to an integer in the range of 2 to 8 enables the
canvas option.
Setting orientation to true enables the canvas and meta options, unless
the browser supports automatic image orientation (see browser support for image-orientation).
meta
Automatically parses the image meta data if set to true.
The meta data is passed to the callback as part of the second argument.
If the file is given as URL and the browser supports the
fetch API, fetches
the file as Blob to be able to parse the meta data.
canvas
Returns the image as canvas
element if set to true.
crossOrigin
Sets the crossOrigin property on the img element for loading CORS enabled images.
noRevoke
By default, the
created object URL
is revoked after the image has been loaded, except when this option is set to
true.
Meta data parsing
If the Load Image Meta extension is included, it is also possible to parse image
meta data automatically with the meta option:
loadImage(
fileOrBlobOrUrl,
function (img, data) {
console.log('Original image head: ', data.imageHead)
console.log('Exif data: ', data.exif) // requires exif extension
console.log('IPTC data: ', data.iptc) // requires iptc extension
},
{ meta: true }
)
Or alternatively via loadImage.parseMetaData, which can be used with an
available File or Blob object as first argument:
loadImage.parseMetaData(
fileOrBlob,
function (data) {
console.log('Original image head: ', data.imageHead)
console.log('Exif data: ', data.exif) // requires exif extension
console.log('IPTC data: ', data.iptc) // requires iptc extension
},
{
maxMetaDataSize: 262144
}
)
The Meta data extension also adds additional options used for the
parseMetaData method:
-
maxMetaDataSize: Maximum number of bytes of meta data to parse. -
disableImageHead: Disable parsing the original image head. -
disableMetaDataParsers: Disable parsing meta data (image head only)
Image head
Resized JPEG images can be combined with their original image head via
loadImage.replaceHead, which requires the resized image as Blob object as
first argument and an ArrayBuffer image head as second argument. The third
argument must be a callback function, which is called with the new Blob
object:
loadImage(
fileOrBlobOrUrl,
function (img, data) {
if (data.imageHead && data.exif) {
img.toBlob(function (blob) {
loadImage.replaceHead(blob, data.imageHead, function (newBlob) {
// do something with newBlob
})
}, 'image/jpeg')
}
},
{ meta: true, canvas: true, maxWidth: 800 }
)
Note:
Blob objects of resized images can be created via
canvas.toBlob.
For browsers which don't have native support, a
canvas.toBlob polyfill
is available.
Exif parser
If you include the Load Image Exif Parser extension, the argument passed to the
callback for parseMetaData will contain the following additional properties if
Exif data could be found in the given image:
-
exif: The parsed Exif tags -
exifOffsets: The parsed Exif tag offsets -
exifTiffOffset: TIFF header offset (used for offset pointers) -
exifLittleEndian: little endian order if true, big endian if false
The exif object stores the parsed Exif tags:
var orientation = data.exif[0x0112] // Orientation
The exif and exifOffsets objects also provide a get() method to retrieve
the tag value/offset via the tag's mapped name:
var orientation = data.exif.get('Orientation')
var orientationOffset = data.exifOffsets.get('Orientation')
By default, only the following names are mapped:
OrientationThumbnailExifGPSInfoInteroperability
If you also include the Load Image Exif Map library, additional tag mappings become available, as well as three additional methods:
exif.getText()exif.getName()exif.getAll()
var flashText = data.exif.getText('Flash') // e.g.: 'Flash fired, auto mode',
var name = data.exif.getName(0x0112) // Orientation
// A map of all parsed tags with their mapped names/text as keys/values:
var allTags = data.exif.getAll()
The Exif parser also adds additional options for the parseMetaData method, to disable certain aspects of the parser:
-
disableExif: Disables Exif parsing whentrue. -
disableExifThumbnail: Disables parsing of Thumbnail data whentrue. -
disableExifOffsets: Disables storing Exif tag offsets whentrue. -
includeExifTags: A map of Exif tags to include for parsing (includes all but the excluded tags by default). -
excludeExifTags: A map of Exif tags to exclude from parsing (defaults to excludeExifMakerNote).
An example parsing only Orientation, Thumbnail and ExifVersion tags:
loadImage.parseMetaData(
fileOrBlob,
function (data) {
console.log('Exif data: ', data.exif)
},
{
includeExifTags: {
0x0112: true, // Orientation
0x0201: true, // JPEGInterchangeFormat (Thumbnail data offset)
0x0202: true, // JPEGInterchangeFormatLength (Thumbnail data length)
0x8769: {
// ExifIFDPointer
0x9000: true // ExifVersion
}
}
}
)
An example excluding Exif MakerNote and GPSInfo:
loadImage.parseMetaData(
fileOrBlob,
function (data) {
console.log('Exif data: ', data.exif)
},
{
excludeExifTags: {
0x8769: {
// ExifIFDPointer
0x927c: true // MakerNote
},
0x8825: true // GPSInfoIFDPointer
}
}
)
Exif writer
The Exif parser extension also includes a minimal writer that allows to override
the Exif Orientation value in the parsed imageHead ArrayBuffer:
loadImage(
fileOrBlobOrUrl,
function (img, data) {
if (data.imageHead && data.exif) {
// Reset Exif Orientation data:
loadImage.writeExifData(data.imageHead, data, 'Orientation', 1)
img.toBlob(function (blob) {
loadImage.replaceHead(blob, data.imageHead, function (newBlob) {
// do something with newBlob
})
}, 'image/jpeg')
}
},
{ meta: true, orientation: true, canvas: true, maxWidth: 800 }
)
IPTC parser
If you include the Load Image IPTC Parser extension, the argument passed to the
callback for parseMetaData will contain the following additional properties if
IPTC data could be found in the given image:
-
iptc: The parsed IPTC tags -
iptcOffsets: The parsed IPTC tag offsets
The iptc object stores the parsed IPTC tags:
var objectname = data.iptc[5]
The iptc and iptcOffsets objects also provide a get() method to retrieve
the tag value/offset via the tag's mapped name:
var objectname = data.iptc.get('ObjectName')
By default, only the following names are mapped:
ObjectName
If you also include the Load Image IPTC Map library, additional tag mappings become available, as well as three additional methods:
iptc.getText()iptc.getName()iptc.getAll()
var keywords = data.iptc.getText('Keywords') // e.g.: ['Weather','Sky']
var name = data.iptc.getName(5) // ObjectName
// A map of all parsed tags with their mapped names/text as keys/values:
var allTags = data.iptc.getAll()
The IPTC parser also adds additional options for the parseMetaData method, to disable certain aspects of the parser:
-
disableIptc: Disables IPTC parsing when true. -
disableIptcOffsets: Disables storing IPTC tag offsets whentrue. -
includeIptcTags: A map of IPTC tags to include for parsing (includes all but the excluded tags by default). -
excludeIptcTags: A map of IPTC tags to exclude from parsing (defaults to excludeObjectPreviewData).
An example parsing only the ObjectName tag:
loadImage.parseMetaData(
fileOrBlob,
function (data) {
console.log('IPTC data: ', data.iptc)
},
{
includeIptcTags: {
5: true // ObjectName
}
}
)
An example excluding ApplicationRecordVersion and ObjectPreviewData:
loadImage.parseMetaData(
fileOrBlob,
function (data) {
console.log('IPTC data: ', data.iptc)
},
{
excludeIptcTags: {
0: true, // ApplicationRecordVersion
202: true // ObjectPreviewData
}
}
)
License
The JavaScript Load Image script is released under the MIT license.
Credits
- Image meta data handling implementation based on the help and contribution of Achim Stöhr.
- Exif tags mapping based on Jacob Seidelin's exif-js library.
- IPTC parser implementation by Dave Bevan.