Use HTML5 to resize an image before upload
if any interested I've made a typescript version:
interface IResizeImageOptions {
maxSize: number;
file: File;
}
const resizeImage = (settings: IResizeImageOptions) => {
const file = settings.file;
const maxSize = settings.maxSize;
const reader = new FileReader();
const image = new Image();
const canvas = document.createElement('canvas');
const dataURItoBlob = (dataURI: string) => {
const bytes = dataURI.split(',')[0].indexOf('base64') >= 0 ?
atob(dataURI.split(',')[1]) :
unescape(dataURI.split(',')[1]);
const mime = dataURI.split(',')[0].split(':')[1].split(';')[0];
const max = bytes.length;
const ia = new Uint8Array(max);
for (var i = 0; i < max; i++) ia[i] = bytes.charCodeAt(i);
return new Blob([ia], {type:mime});
};
const resize = () => {
let width = image.width;
let height = image.height;
if (width > height) {
if (width > maxSize) {
height *= maxSize / width;
width = maxSize;
}
} else {
if (height > maxSize) {
width *= maxSize / height;
height = maxSize;
}
}
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
let dataUrl = canvas.toDataURL('image/jpeg');
return dataURItoBlob(dataUrl);
};
return new Promise((ok, no) => {
if (!file.type.match(/image.*/)) {
no(new Error("Not an image"));
return;
}
reader.onload = (readerEvent: any) => {
image.onload = () => ok(resize());
image.src = readerEvent.target.result;
};
reader.readAsDataURL(file);
})
};
and here's the javascript result:
var resizeImage = function (settings) {
var file = settings.file;
var maxSize = settings.maxSize;
var reader = new FileReader();
var image = new Image();
var canvas = document.createElement('canvas');
var dataURItoBlob = function (dataURI) {
var bytes = dataURI.split(',')[0].indexOf('base64') >= 0 ?
atob(dataURI.split(',')[1]) :
unescape(dataURI.split(',')[1]);
var mime = dataURI.split(',')[0].split(':')[1].split(';')[0];
var max = bytes.length;
var ia = new Uint8Array(max);
for (var i = 0; i < max; i++)
ia[i] = bytes.charCodeAt(i);
return new Blob([ia], { type: mime });
};
var resize = function () {
var width = image.width;
var height = image.height;
if (width > height) {
if (width > maxSize) {
height *= maxSize / width;
width = maxSize;
}
} else {
if (height > maxSize) {
width *= maxSize / height;
height = maxSize;
}
}
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
var dataUrl = canvas.toDataURL('image/jpeg');
return dataURItoBlob(dataUrl);
};
return new Promise(function (ok, no) {
if (!file.type.match(/image.*/)) {
no(new Error("Not an image"));
return;
}
reader.onload = function (readerEvent) {
image.onload = function () { return ok(resize()); };
image.src = readerEvent.target.result;
};
reader.readAsDataURL(file);
});
};
usage is like:
resizeImage({
file: $image.files[0],
maxSize: 500
}).then(function (resizedImage) {
console.log("upload resized image")
}).catch(function (err) {
console.error(err);
});
or (async/await):
const config = {
file: $image.files[0],
maxSize: 500
};
const resizedImage = await resizeImage(config)
console.log("upload resized image")
Here is what I ended up doing and it worked great.
First I moved the file input outside of the form so that it is not submitted:
<input name="imagefile[]" type="file" id="takePictureField" accept="image/*" onchange="uploadPhotos(\'#{imageUploadUrl}\')" />
<form id="uploadImageForm" enctype="multipart/form-data">
<input id="name" value="#{name}" />
... a few more inputs ...
</form>
Then I changed the uploadPhotos function to handle only the resizing:
window.uploadPhotos = function(url){
// Read in file
var file = event.target.files[0];
// Ensure it's an image
if(file.type.match(/image.*/)) {
console.log('An image has been loaded');
// Load the image
var reader = new FileReader();
reader.onload = function (readerEvent) {
var image = new Image();
image.onload = function (imageEvent) {
// Resize the image
var canvas = document.createElement('canvas'),
max_size = 544,// TODO : pull max size from a site config
width = image.width,
height = image.height;
if (width > height) {
if (width > max_size) {
height *= max_size / width;
width = max_size;
}
} else {
if (height > max_size) {
width *= max_size / height;
height = max_size;
}
}
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
var dataUrl = canvas.toDataURL('image/jpeg');
var resizedImage = dataURLToBlob(dataUrl);
$.event.trigger({
type: "imageResized",
blob: resizedImage,
url: dataUrl
});
}
image.src = readerEvent.target.result;
}
reader.readAsDataURL(file);
}
};
As you can see I'm using canvas.toDataURL('image/jpeg'); to change the resized image into a dataUrl adn then I call the function dataURLToBlob(dataUrl); to turn the dataUrl into a blob that I can then append to the form. When the blob is created, I trigger a custom event. Here is the function to create the blob:
/* Utility function to convert a canvas to a BLOB */
var dataURLToBlob = function(dataURL) {
var BASE64_MARKER = ';base64,';
if (dataURL.indexOf(BASE64_MARKER) == -1) {
var parts = dataURL.split(',');
var contentType = parts[0].split(':')[1];
var raw = parts[1];
return new Blob([raw], {type: contentType});
}
var parts = dataURL.split(BASE64_MARKER);
var contentType = parts[0].split(':')[1];
var raw = window.atob(parts[1]);
var rawLength = raw.length;
var uInt8Array = new Uint8Array(rawLength);
for (var i = 0; i < rawLength; ++i) {
uInt8Array[i] = raw.charCodeAt(i);
}
return new Blob([uInt8Array], {type: contentType});
}
/* End Utility function to convert a canvas to a BLOB */
Finally, here is my event handler that takes the blob from the custom event, appends the form and then submits it.
/* Handle image resized events */
$(document).on("imageResized", function (event) {
var data = new FormData($("form[id*='uploadImageForm']")[0]);
if (event.blob && event.url) {
data.append('image_data', event.blob);
$.ajax({
url: event.url,
data: data,
cache: false,
contentType: false,
processData: false,
type: 'POST',
success: function(data){
//handle errors...
}
});
}
});