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I am trying to compress images on client side using JavaScript on some low bandwidth devices and I'm currently stuck in a limbo using the HTML5 File API. I'm new to this, please bear with me if I'm missing something important.
I have some input tags which should ideally open the mobile camera, capture single image, compress and send files to the backend. Although this can be done with a single input field with multiple uploads enabled but I need the multiple image fields to segregate images based on some categories.
Here's the input boxes:
<input type="file" name="file1" id="file1" capture="camera" accept="image/*">
<input type="file" name="file2" id="file2" capture="camera" accept="image/*">...
Here's the image compression logic:
// Takes upload element id ("file1") and a maxSize to resize, ideally on a change event
window.resizePhotos = function(id, maxSize){
var file = document.getElementById(id).files[0];
// Ensuring it's an image
if(file.type.match(/image.*/)) {
// Loading the image
var reader = new FileReader();
reader.onload = function (readerEvent) {
var image = new Image();
image.onload = function (imageEvent) {
// Resizing the image and keeping its aspect ratio
var canvas = document.createElement("canvas"),
max_size = maxSize,
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);
}
};
// 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});
}
// Handling image resized events
$(document).on("imageResized", function (event) {
if (event.blob && event.url) {
document.getElementById('file1').files[0] = event.url; // --> Tried this, did not work
document.getElementById('file1').files[0].value = (URL || webkitURL).createObjectURL(event.blob); // --> Tried doing this looking at some other answers but did not work
console.log(document.getElementById('file1').files[0]); // Original file is loading fine
console.log(event.url); // Image compression is working correctly and producing the base64 data
}
});
$(window).on("load", function() {
// Resets the value to when navigating away from the page and choosing to upload the same file (extra feature)
$("#file1").on("click touchstart" , function(){
$(this).val("");
});
// Action triggers when user has selected any file
$("#file1").change(function(e) {
resizePhotos("file1", 1024)
});
});
In PHP script, I'd usually try to catch files from the POST request like:
$file1 = $_FILES["file1"]["tmp_name"];
$file2 = $_FILES["file2"]["tmp_name"];
...
But this doesn't work because it looks for the original user selected file at a tmp directory (e.g. the actual temporary file in my case is C:\xampp\tmp\php25CB.tmp )
One thing I've tried is put the input fields outside of the form tags, enabled the click behaviour using a button and created new input field with the modified data within the form like:
var newinput = document.createElement("input");
newinput.type = 'file';
newinput.name = 'file1';
newinput.files[0] = event.url;
document.getElementById('parentdiv').appendChild(newinput);
Needless to say, this had no effect and the PHP script could not identify any file.
Please guide me and suggest any changes required in the JavaScript/PHP script so I can accept the modified file and not the original user uploaded file from the input field.
You can only change a file input value with another list here is how: https://stackoverflow.com/a/52079109/1008999 (also in the example)
Using the FileReader is a waste of time, CPU, Encoding & decoding and RAM...use URL.createObjectURL instead
Don't use canvas.toDataURL... use canvas.toBlob instead
Canvas have bad compression, read earlier comment and see the jsfiddle proff...If you insist on using canvas to try and squeeze the size down then
First try to see if the image is in a reasonable size first
Compare if the pre existing image file.size is smaller than what the canvas.toBlob provides and choose if you want the old or the new one instead.
If resizing the image isn't enough have a look at this solution that change the quality until a desired file size & image aspect have been meet.
Without any testing, this is how i would have refactor your code too:
/**
* #params {File[]} files Array of files to add to the FileList
* #return {FileList}
*/
function fileListItems (files) {
var b = new ClipboardEvent('').clipboardData || new DataTransfer()
for (var i = 0, len = files.length; i<len; i++) b.items.add(files[i])
return b.files
}
// Takes upload element id ("file1") and a maxSize to resize, ideally on a change event
window.resizePhotos = async function resizePhotos (input, maxSize) {
const file = input.files
if (!file || !file.type.match(/image.*/)) return
const image = new Image()
const canvas = document.createElement('canvas')
const max_size = maxSize
image.src = URL.createObjectURL(file)
await image.decode()
let width = image.width
let height = image.height
// Resizing the image and keeping its aspect ratio
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)
const resizedImage = await new Promise(rs => canvas.toBlob(rs, 'image/jpeg', 1))
// PS: You might have to disable the event listener as this might case a change event
// and triggering this function over and over in a loop otherwise
input.files = fileListItems([
new File([resizedImage], file.name, { type: resizedImage.type })
])
}
jQuery($ => {
// Resets the value to when navigating away from the page and choosing to upload the same file (extra feature)
$('#file1').on('click touchstart' , function(){
$(this).val('')
})
// Action triggers when user has selected any file
$('#file1').change(function(e) {
resizePhotos(this, 1024)
})
})
I'm trying to get a base64 encoded png value from a canvas that was created by converting a pdf with the PDF.JS library by Mozilla.
So I had a base64 encoded PDF that I converted into a HTML canvas. I now need to convert that HTML canvas into a base64 encoded png value that I can use with a HTML img tag that displays properly.
I tried the HTMLCanvasElement.toDataURL(), however it doesn't display anything. I tried using the same method with some green boxes drawn in canvas and it worked fine, meaning that the base64 encoded pdf converted to canvas just doesn't want to work with that method.
Any other solutions or a workaround for the solution I tried?
**I need to do this inside my JS code with my HTML.
function convertDataURIToBinary() {
var raw = window.atob(BASE64 OF PDF);
var rawLength = raw.length;
var array = new Uint8Array(new ArrayBuffer(rawLength));
for(var i = 0; i < rawLength; i++) {
array[i] = raw.charCodeAt(i);
}
return array;
}
var pdfAsArray = convertDataURIToBinary();
PDFJS.workerSrc = "http://mozilla.github.io/pdf.js/build/pdf.worker.js";
var canvas = _el.querySelector(".insertHere");
PDFJS.getDocument(pdfAsArray).then(function getPdfHelloWorld(pdf) {
pdf.getPage(1).then(function getPageHelloWorld(page) {
var scale = 1.5;
var viewport = page.getViewport(scale);
var context = canvas.getContext("2d");
canvas.height = viewport.height;
canvas.width = viewport.width;
var renderContext = {
canvasContext: context,
viewport: viewport
};
page.render(renderContext);
canvas = _el.querySelector(".insertHere");
var imgSrc = canvas.toDataURL("image/png");
var img = new Image();
img.src = imgSrc;
_el.querySelector(".insertImageLabel").appendChild(img);
});
});
You are not waiting on the promise returned by render() to finish async operation. See https://github.com/mozilla/pdf.js/blob/master/examples/learning/prevnext.html#L76 how to wait on completion:
...
var renderTask = page.render(renderContext);
// Wait for rendering to finish
renderTask.promise.then(function () {
// Page rendered, now take snapshot.
});
...
TL;DR;
Is there a way to compress an image (mostly jpeg, png and gif) directly browser-side, before uploading it ? I'm pretty sure JavaScript can do this, but I can't find a way to achieve it.
Here's the full scenario I would like to implement:
the user goes to my website, and choose an image via an input type="file" element,
this image is retrieved via JavaScript, we do some verification such as correct file format, maximum file size etc,
if every thing is OK, a preview of the image is displayed on the page,
the user can do some basic operations such as rotate the image by 90°/-90°, crop it following a pre-defined ratio, etc, or the user can upload another image and return to step 1,
when the user is satisfied, the edited image is then compressed and "saved" locally (not saved to a file, but in the browser memory/page),-
the user fill a form with data like name, age etc,
the user click on the "Finish" button, then the form containing datas + compressed image is sent to the server (without AJAX),
The full process up to the last step should be done client side, and should be compatible on latest Chrome and Firefox, Safari 5+ and IE 8+. If possible, only JavaScript should be used (but I'm pretty sure this is not possible).
I've not code anything right now, but I've thought about it already. File reading locally is possible via File API, image previewing and editing could be done using Canvas element, but I can't find a way to do the image compression part.
According to html5please.com and caniuse.com, supporting those browser is quite hard (thanks to IE), but could be done using polyfill such as FlashCanvas and FileReader.
Actually, the goal is to reduce file size, so I see image compression as a solution. But, I know that uploaded images are going to be displayed on my website, every time at the same place, and I know the dimension of this display area (eg. 200x400). So, I could resize the image to fit those dimensions, thus reducing file size. I have no idea what would be the compression ratio for this technique.
What do you think ? Do you have any advice to tell me ? Do you know any way to compress an image browser-side in JavaScript ? Thanks for your replies.
In short:
Read the files using the HTML5 FileReader API with .readAsArrayBuffer
Create a Blob with the file data and get its url with window.URL.createObjectURL(blob)
Create new Image element and set it's src to the file blob url
Send the image to the canvas. The canvas size is set to desired output size
Get the scaled-down data back from canvas via canvas.toDataURL("image/jpeg",0.7) (set your own output format and quality)
Attach new hidden inputs to the original form and transfer the dataURI images basically as normal text
On backend, read the dataURI, decode from Base64, and save it
Source: code.
I see two things missing from the other answers:
canvas.toBlob (when available) is more performant than canvas.toDataURL, and also async.
the file -> image -> canvas -> file conversion loses EXIF data; in particular, data about image rotation commonly set by modern phones/tablets.
The following script deals with both points:
// From https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob, needed for Safari:
if (!HTMLCanvasElement.prototype.toBlob) {
Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
value: function(callback, type, quality) {
var binStr = atob(this.toDataURL(type, quality).split(',')[1]),
len = binStr.length,
arr = new Uint8Array(len);
for (var i = 0; i < len; i++) {
arr[i] = binStr.charCodeAt(i);
}
callback(new Blob([arr], {type: type || 'image/png'}));
}
});
}
window.URL = window.URL || window.webkitURL;
// Modified from https://stackoverflow.com/a/32490603, cc by-sa 3.0
// -2 = not jpeg, -1 = no data, 1..8 = orientations
function getExifOrientation(file, callback) {
// Suggestion from http://code.flickr.net/2012/06/01/parsing-exif-client-side-using-javascript-2/:
if (file.slice) {
file = file.slice(0, 131072);
} else if (file.webkitSlice) {
file = file.webkitSlice(0, 131072);
}
var reader = new FileReader();
reader.onload = function(e) {
var view = new DataView(e.target.result);
if (view.getUint16(0, false) != 0xFFD8) {
callback(-2);
return;
}
var length = view.byteLength, offset = 2;
while (offset < length) {
var marker = view.getUint16(offset, false);
offset += 2;
if (marker == 0xFFE1) {
if (view.getUint32(offset += 2, false) != 0x45786966) {
callback(-1);
return;
}
var little = view.getUint16(offset += 6, false) == 0x4949;
offset += view.getUint32(offset + 4, little);
var tags = view.getUint16(offset, little);
offset += 2;
for (var i = 0; i < tags; i++)
if (view.getUint16(offset + (i * 12), little) == 0x0112) {
callback(view.getUint16(offset + (i * 12) + 8, little));
return;
}
}
else if ((marker & 0xFF00) != 0xFF00) break;
else offset += view.getUint16(offset, false);
}
callback(-1);
};
reader.readAsArrayBuffer(file);
}
// Derived from https://stackoverflow.com/a/40867559, cc by-sa
function imgToCanvasWithOrientation(img, rawWidth, rawHeight, orientation) {
var canvas = document.createElement('canvas');
if (orientation > 4) {
canvas.width = rawHeight;
canvas.height = rawWidth;
} else {
canvas.width = rawWidth;
canvas.height = rawHeight;
}
if (orientation > 1) {
console.log("EXIF orientation = " + orientation + ", rotating picture");
}
var ctx = canvas.getContext('2d');
switch (orientation) {
case 2: ctx.transform(-1, 0, 0, 1, rawWidth, 0); break;
case 3: ctx.transform(-1, 0, 0, -1, rawWidth, rawHeight); break;
case 4: ctx.transform(1, 0, 0, -1, 0, rawHeight); break;
case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;
case 6: ctx.transform(0, 1, -1, 0, rawHeight, 0); break;
case 7: ctx.transform(0, -1, -1, 0, rawHeight, rawWidth); break;
case 8: ctx.transform(0, -1, 1, 0, 0, rawWidth); break;
}
ctx.drawImage(img, 0, 0, rawWidth, rawHeight);
return canvas;
}
function reduceFileSize(file, acceptFileSize, maxWidth, maxHeight, quality, callback) {
if (file.size <= acceptFileSize) {
callback(file);
return;
}
var img = new Image();
img.onerror = function() {
URL.revokeObjectURL(this.src);
callback(file);
};
img.onload = function() {
URL.revokeObjectURL(this.src);
getExifOrientation(file, function(orientation) {
var w = img.width, h = img.height;
var scale = (orientation > 4 ?
Math.min(maxHeight / w, maxWidth / h, 1) :
Math.min(maxWidth / w, maxHeight / h, 1));
h = Math.round(h * scale);
w = Math.round(w * scale);
var canvas = imgToCanvasWithOrientation(img, w, h, orientation);
canvas.toBlob(function(blob) {
console.log("Resized image to " + w + "x" + h + ", " + (blob.size >> 10) + "kB");
callback(blob);
}, 'image/jpeg', quality);
});
};
img.src = URL.createObjectURL(file);
}
Example usage:
inputfile.onchange = function() {
// If file size > 500kB, resize such that width <= 1000, quality = 0.9
reduceFileSize(this.files[0], 500*1024, 1000, Infinity, 0.9, blob => {
let body = new FormData();
body.set('file', blob, blob.name || "file.jpg");
fetch('/upload-image', {method: 'POST', body}).then(...);
});
};
#PsychoWoods' answer is good. I would like to offer my own solution. This Javascript function takes an image data URL and a width, scales it to the new width, and returns a new data URL.
// Take an image URL, downscale it to the given width, and return a new image URL.
function downscaleImage(dataUrl, newWidth, imageType, imageArguments) {
"use strict";
var image, oldWidth, oldHeight, newHeight, canvas, ctx, newDataUrl;
// Provide default values
imageType = imageType || "image/jpeg";
imageArguments = imageArguments || 0.7;
// Create a temporary image so that we can compute the height of the downscaled image.
image = new Image();
image.src = dataUrl;
oldWidth = image.width;
oldHeight = image.height;
newHeight = Math.floor(oldHeight / oldWidth * newWidth)
// Create a temporary canvas to draw the downscaled image on.
canvas = document.createElement("canvas");
canvas.width = newWidth;
canvas.height = newHeight;
// Draw the downscaled image on the canvas and return the new data URL.
ctx = canvas.getContext("2d");
ctx.drawImage(image, 0, 0, newWidth, newHeight);
newDataUrl = canvas.toDataURL(imageType, imageArguments);
return newDataUrl;
}
This code can be used anywhere you have a data URL and want a data URL for a downscaled image.
You can take a look at image-conversion,Try it here --> demo page
Try this Customizable Pure JS Sample - Compress over 90% :
<div id="root">
<p>Upload an image and see the result</p>
<input id="img-input" type="file" accept="image/*" style="display:block" />
</div>
<script>
const MAX_WIDTH = 320;
const MAX_HEIGHT = 180;
const MIME_TYPE = "image/jpeg";
const QUALITY = 0.7;
const input = document.getElementById("img-input");
input.onchange = function (ev) {
const file = ev.target.files[0]; // get the file
const blobURL = URL.createObjectURL(file);
const img = new Image();
img.src = blobURL;
img.onerror = function () {
URL.revokeObjectURL(this.src);
// Handle the failure properly
console.log("Cannot load image");
};
img.onload = function () {
URL.revokeObjectURL(this.src);
const [newWidth, newHeight] = calculateSize(img, MAX_WIDTH, MAX_HEIGHT);
const canvas = document.createElement("canvas");
canvas.width = newWidth;
canvas.height = newHeight;
const ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, newWidth, newHeight);
canvas.toBlob(
(blob) => {
// Handle the compressed image. es. upload or save in local state
displayInfo('Original file', file);
displayInfo('Compressed file', blob);
},
MIME_TYPE,
QUALITY
);
document.getElementById("root").append(canvas);
};
};
function calculateSize(img, maxWidth, maxHeight) {
let width = img.width;
let height = img.height;
// calculate the width and height, constraining the proportions
if (width > height) {
if (width > maxWidth) {
height = Math.round((height * maxWidth) / width);
width = maxWidth;
}
} else {
if (height > maxHeight) {
width = Math.round((width * maxHeight) / height);
height = maxHeight;
}
}
return [width, height];
}
// Utility functions for demo purpose
function displayInfo(label, file) {
const p = document.createElement('p');
p.innerText = `${label} - ${readableBytes(file.size)}`;
document.getElementById('root').append(p);
}
function readableBytes(bytes) {
const i = Math.floor(Math.log(bytes) / Math.log(1024)),
sizes = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
return (bytes / Math.pow(1024, i)).toFixed(2) + ' ' + sizes[i];
}
</script>
I find that there's simpler solution compared to the accepted answer.
Read the files using the HTML5 FileReader API with .readAsArrayBuffer
Create a Blob with the file data and get its url with window.URL.createObjectURL(blob)
Create new Image element and set it's src to the file blob url
Send the image to the canvas. The canvas size is set to desired output size
Get the scaled-down data back from canvas via canvas.toDataURL("image/jpeg",0.7) (set your own output format and quality)
Attach new hidden inputs to the original form and transfer the dataURI images basically as normal text
On backend, read the dataURI, decode from Base64, and save it
As per your question:
Is there a way to compress an image (mostly jpeg, png and gif)
directly browser-side, before uploading it
My solution:
Create a blob with the file directly with URL.createObjectURL(inputFileElement.files[0]).
Same as accepted answer.
Same as accepted answer. Worth mentioning that, canvas size is necessary and use img.width and img.height to set canvas.width and canvas.height. Not img.clientWidth.
Get the scale-down image by canvas.toBlob(callbackfunction(blob){}, 'image/jpeg', 0.5). Setting 'image/jpg' has no effect. image/png is also supported. Make a new File object inside the callbackfunction body with let compressedImageBlob = new File([blob]).
Add new hidden inputs or send via javascript . Server doesn't have to decode anything.
Check https://javascript.info/binary for all information. I came up the solution after reading this chapter.
Code:
<!DOCTYPE html>
<html>
<body>
<form action="upload.php" method="post" enctype="multipart/form-data">
Select image to upload:
<input type="file" name="fileToUpload" id="fileToUpload" multiple>
<input type="submit" value="Upload Image" name="submit">
</form>
</body>
</html>
This code looks far less scary than the other answers..
Update:
One has to put everything inside img.onload. Otherwise canvas will not be able to get the image's width and height correctly as the time canvas is assigned.
function upload(){
var f = fileToUpload.files[0];
var fileName = f.name.split('.')[0];
var img = new Image();
img.src = URL.createObjectURL(f);
img.onload = function(){
var canvas = document.createElement('canvas');
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
canvas.toBlob(function(blob){
console.info(blob.size);
var f2 = new File([blob], fileName + ".jpeg");
var xhr = new XMLHttpRequest();
var form = new FormData();
form.append("fileToUpload", f2);
xhr.open("POST", "upload.php");
xhr.send(form);
}, 'image/jpeg', 0.5);
}
}
3.4MB .png file compression test with image/jpeg argument set.
|0.9| 777KB |
|0.8| 383KB |
|0.7| 301KB |
|0.6| 251KB |
|0.5| 219kB |
I had an issue with the downscaleImage() function posted above by #daniel-allen-langdon in that the image.width and image.height properties are not available immediately because the image load is asynchronous.
Please see updated TypeScript example below that takes this into account, uses async functions, and resizes the image based on the longest dimension rather than just the width
function getImage(dataUrl: string): Promise<HTMLImageElement>
{
return new Promise((resolve, reject) => {
const image = new Image();
image.src = dataUrl;
image.onload = () => {
resolve(image);
};
image.onerror = (el: any, err: ErrorEvent) => {
reject(err.error);
};
});
}
export async function downscaleImage(
dataUrl: string,
imageType: string, // e.g. 'image/jpeg'
resolution: number, // max width/height in pixels
quality: number // e.g. 0.9 = 90% quality
): Promise<string> {
// Create a temporary image so that we can compute the height of the image.
const image = await getImage(dataUrl);
const oldWidth = image.naturalWidth;
const oldHeight = image.naturalHeight;
console.log('dims', oldWidth, oldHeight);
const longestDimension = oldWidth > oldHeight ? 'width' : 'height';
const currentRes = longestDimension == 'width' ? oldWidth : oldHeight;
console.log('longest dim', longestDimension, currentRes);
if (currentRes > resolution) {
console.log('need to resize...');
// Calculate new dimensions
const newSize = longestDimension == 'width'
? Math.floor(oldHeight / oldWidth * resolution)
: Math.floor(oldWidth / oldHeight * resolution);
const newWidth = longestDimension == 'width' ? resolution : newSize;
const newHeight = longestDimension == 'height' ? resolution : newSize;
console.log('new width / height', newWidth, newHeight);
// Create a temporary canvas to draw the downscaled image on.
const canvas = document.createElement('canvas');
canvas.width = newWidth;
canvas.height = newHeight;
// Draw the downscaled image on the canvas and return the new data URL.
const ctx = canvas.getContext('2d')!;
ctx.drawImage(image, 0, 0, newWidth, newHeight);
const newDataUrl = canvas.toDataURL(imageType, quality);
return newDataUrl;
}
else {
return dataUrl;
}
}
For Moderm browser use createImageBitmap() instead of img.onload
async function compressImage(blobImg, percent) {
let bitmap = await createImageBitmap(blobImg);
let canvas = document.createElement("canvas");
let ctx = canvas.getContext("2d");
canvas.width = bitmap.width;
canvas.height = bitmap.height;
ctx.drawImage(bitmap, 0, 0);
let dataUrl = canvas.toDataURL("image/jpeg", percent/100);
return dataUrl;
}
inputImg.addEventListener('change', async(e) => {
let img = e.target.files[0];
console.log('File Name: ', img.name)
console.log('Original Size: ', img.size.toLocaleString())
let imgCompressed = await compressImage(img, 75) // set to 75%
let compSize = atob(imgCompressed.split(",")[1]).length;
console.log('Compressed Size: ', compSize.toLocaleString())
//console.log(imgCompressed)
})
<input type="file" id="inputImg">
Edit: As per the Mr Me comment on this answer, it looks like compression is now available for JPG/WebP formats ( see https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL ).
As far as I know, you cannot compress images using canvas, instead, you can resize it. Using canvas.toDataURL will not let you choose the compression ratio to use. You can take a look at canimage that does exactly what you want : https://github.com/nfroidure/CanImage/blob/master/chrome/canimage/content/canimage.js
In fact, it's often sufficient to just resize the image to decrease it's size but if you want to go further, you'll have to use newly introduced method file.readAsArrayBuffer to get a buffer containing the image data.
Then, just use a DataView to read it's content according to the image format specification (http://en.wikipedia.org/wiki/JPEG or http://en.wikipedia.org/wiki/Portable_Network_Graphics).
It'll be hard to deal with image data compression, but it is worse a try. On the other hand, you can try to delete the PNG headers or the JPEG exif data to make your image smaller, it should be easier to do so.
You'll have to create another DataWiew on another buffer and fill it with the filtered image content. Then, you'll just have to encode you're image content to DataURI using window.btoa.
Let me know if you implement something similar, will be interesting to go through the code.
Compressor.js
https://github.com/fengyuanchen/compressorjs
import axios from 'axios';
import Compressor from 'compressorjs';
document.getElementById('file').addEventListener('change', (e) => {
const file = e.target.files[0];
if (!file) {
return;
}
new Compressor(file, {
quality: 0.6,
// The compression process is asynchronous,
// which means you have to access the `result` in the `success` hook function.
success(result) {
const formData = new FormData();
// The third parameter is required for server
formData.append('file', result, result.name);
// Send the compressed image file to server with XMLHttpRequest.
axios.post('/path/to/upload', formData).then(() => {
console.log('Upload success');
});
},
error(err) {
console.log(err.message);
},
});
});
I used the following package:
https://www.npmjs.com/package/browser-image-compression
npm install browser-image-compression
or
yarn add browser-image-compression
Then just following the docs:
import imageCompression from 'browser-image-compression';
const options = {
maxSizeMB: 0.5, // pretty much self-explanatory
maxWidthOrHeight: 500, // apparently px
}
imageCompression(file, options)
.then(function(compressedFile) {
console.log(
"compressedFile instanceof Blob",
compressedFile instanceof Blob
); // true
console.log(
`compressedFile size ${compressedFile.size /
1024 /
1024} MB`
); // smaller than maxSizeMB
return uploader(compressedFile); // code to actual upload, in my case uploader() is a function to upload to Firebase storage.
})
Just in case if you were curios about the uploader(), here's the code of it:
import { initializeApp } from "firebase/app";
const firebaseConfig = {
// your config
};
initializeApp(firebaseConfig);
import { getStorage, ref, uploadBytes, getDownloadURL } from "firebase/storage";
const storage = getStorage();
const sRef = ref(storage);
const uploader = async (file) => {
/* uploads to root */
// const imageRef = ref(sRef, file.name);
// console.log(imageRef);
// await uploadBytes(imageRef, file).then((snapshot) => {
// console.log("Uploaded a blob or file!", snapshot);
// });
/* upload to folder 'techs/' */
const folderRef = ref(sRef, "techs/" + file.name);
await uploadBytes(folderRef, file);
// get URL
const url = await getDownloadURL(ref(storage, folderRef));
console.log("url: ", url);
return url;
};
You can compress an image using the HTML <canvas> element:
function compressImage(imgToCompress, resizingFactor, quality) {
// resizing the image
const canvas = document.createElement("canvas");
const context = canvas.getContext("2d");
const originalWidth = imgToCompress.width;
const originalHeight = imgToCompress.height;
const canvasWidth = originalWidth * resizingFactor;
const canvasHeight = originalHeight * resizingFactor;
canvas.width = canvasWidth;
canvas.height = canvasHeight;
context.drawImage(
imgToCompress,
0,
0,
originalWidth * resizingFactor,
originalHeight * resizingFactor
);
// reducing the quality of the image
canvas.toBlob(
(blob) => {
if (blob) {
// showing the compressed image
resizedImage.src = URL.createObjectURL(resizedImageBlob);
}
},
"image/jpeg",
quality
);
}
See this blog post for an in depth explanation: https://img.ly/blog/how-to-compress-an-image-before-uploading-it-in-javascript/
i improved the function a head to be this :
var minifyImg = function(dataUrl,newWidth,imageType="image/jpeg",resolve,imageArguments=0.7){
var image, oldWidth, oldHeight, newHeight, canvas, ctx, newDataUrl;
(new Promise(function(resolve){
image = new Image(); image.src = dataUrl;
log(image);
resolve('Done : ');
})).then((d)=>{
oldWidth = image.width; oldHeight = image.height;
log([oldWidth,oldHeight]);
newHeight = Math.floor(oldHeight / oldWidth * newWidth);
log(d+' '+newHeight);
canvas = document.createElement("canvas");
canvas.width = newWidth; canvas.height = newHeight;
log(canvas);
ctx = canvas.getContext("2d");
ctx.drawImage(image, 0, 0, newWidth, newHeight);
//log(ctx);
newDataUrl = canvas.toDataURL(imageType, imageArguments);
resolve(newDataUrl);
});
};
the use of it :
minifyImg(<--DATAURL_HERE-->,<--new width-->,<--type like image/jpeg-->,(data)=>{
console.log(data); // the new DATAURL
});
enjoy ;)
For JPG Image compression you can use the best compression technique called JIC
(Javascript Image Compression)This will definitely help you -->https://github.com/brunobar79/J-I-C
TL;DR;
Is there a way to compress an image (mostly jpeg, png and gif) directly browser-side, before uploading it ? I'm pretty sure JavaScript can do this, but I can't find a way to achieve it.
Here's the full scenario I would like to implement:
the user goes to my website, and choose an image via an input type="file" element,
this image is retrieved via JavaScript, we do some verification such as correct file format, maximum file size etc,
if every thing is OK, a preview of the image is displayed on the page,
the user can do some basic operations such as rotate the image by 90°/-90°, crop it following a pre-defined ratio, etc, or the user can upload another image and return to step 1,
when the user is satisfied, the edited image is then compressed and "saved" locally (not saved to a file, but in the browser memory/page),-
the user fill a form with data like name, age etc,
the user click on the "Finish" button, then the form containing datas + compressed image is sent to the server (without AJAX),
The full process up to the last step should be done client side, and should be compatible on latest Chrome and Firefox, Safari 5+ and IE 8+. If possible, only JavaScript should be used (but I'm pretty sure this is not possible).
I've not code anything right now, but I've thought about it already. File reading locally is possible via File API, image previewing and editing could be done using Canvas element, but I can't find a way to do the image compression part.
According to html5please.com and caniuse.com, supporting those browser is quite hard (thanks to IE), but could be done using polyfill such as FlashCanvas and FileReader.
Actually, the goal is to reduce file size, so I see image compression as a solution. But, I know that uploaded images are going to be displayed on my website, every time at the same place, and I know the dimension of this display area (eg. 200x400). So, I could resize the image to fit those dimensions, thus reducing file size. I have no idea what would be the compression ratio for this technique.
What do you think ? Do you have any advice to tell me ? Do you know any way to compress an image browser-side in JavaScript ? Thanks for your replies.
In short:
Read the files using the HTML5 FileReader API with .readAsArrayBuffer
Create a Blob with the file data and get its url with window.URL.createObjectURL(blob)
Create new Image element and set it's src to the file blob url
Send the image to the canvas. The canvas size is set to desired output size
Get the scaled-down data back from canvas via canvas.toDataURL("image/jpeg",0.7) (set your own output format and quality)
Attach new hidden inputs to the original form and transfer the dataURI images basically as normal text
On backend, read the dataURI, decode from Base64, and save it
Source: code.
I see two things missing from the other answers:
canvas.toBlob (when available) is more performant than canvas.toDataURL, and also async.
the file -> image -> canvas -> file conversion loses EXIF data; in particular, data about image rotation commonly set by modern phones/tablets.
The following script deals with both points:
// From https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob, needed for Safari:
if (!HTMLCanvasElement.prototype.toBlob) {
Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
value: function(callback, type, quality) {
var binStr = atob(this.toDataURL(type, quality).split(',')[1]),
len = binStr.length,
arr = new Uint8Array(len);
for (var i = 0; i < len; i++) {
arr[i] = binStr.charCodeAt(i);
}
callback(new Blob([arr], {type: type || 'image/png'}));
}
});
}
window.URL = window.URL || window.webkitURL;
// Modified from https://stackoverflow.com/a/32490603, cc by-sa 3.0
// -2 = not jpeg, -1 = no data, 1..8 = orientations
function getExifOrientation(file, callback) {
// Suggestion from http://code.flickr.net/2012/06/01/parsing-exif-client-side-using-javascript-2/:
if (file.slice) {
file = file.slice(0, 131072);
} else if (file.webkitSlice) {
file = file.webkitSlice(0, 131072);
}
var reader = new FileReader();
reader.onload = function(e) {
var view = new DataView(e.target.result);
if (view.getUint16(0, false) != 0xFFD8) {
callback(-2);
return;
}
var length = view.byteLength, offset = 2;
while (offset < length) {
var marker = view.getUint16(offset, false);
offset += 2;
if (marker == 0xFFE1) {
if (view.getUint32(offset += 2, false) != 0x45786966) {
callback(-1);
return;
}
var little = view.getUint16(offset += 6, false) == 0x4949;
offset += view.getUint32(offset + 4, little);
var tags = view.getUint16(offset, little);
offset += 2;
for (var i = 0; i < tags; i++)
if (view.getUint16(offset + (i * 12), little) == 0x0112) {
callback(view.getUint16(offset + (i * 12) + 8, little));
return;
}
}
else if ((marker & 0xFF00) != 0xFF00) break;
else offset += view.getUint16(offset, false);
}
callback(-1);
};
reader.readAsArrayBuffer(file);
}
// Derived from https://stackoverflow.com/a/40867559, cc by-sa
function imgToCanvasWithOrientation(img, rawWidth, rawHeight, orientation) {
var canvas = document.createElement('canvas');
if (orientation > 4) {
canvas.width = rawHeight;
canvas.height = rawWidth;
} else {
canvas.width = rawWidth;
canvas.height = rawHeight;
}
if (orientation > 1) {
console.log("EXIF orientation = " + orientation + ", rotating picture");
}
var ctx = canvas.getContext('2d');
switch (orientation) {
case 2: ctx.transform(-1, 0, 0, 1, rawWidth, 0); break;
case 3: ctx.transform(-1, 0, 0, -1, rawWidth, rawHeight); break;
case 4: ctx.transform(1, 0, 0, -1, 0, rawHeight); break;
case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;
case 6: ctx.transform(0, 1, -1, 0, rawHeight, 0); break;
case 7: ctx.transform(0, -1, -1, 0, rawHeight, rawWidth); break;
case 8: ctx.transform(0, -1, 1, 0, 0, rawWidth); break;
}
ctx.drawImage(img, 0, 0, rawWidth, rawHeight);
return canvas;
}
function reduceFileSize(file, acceptFileSize, maxWidth, maxHeight, quality, callback) {
if (file.size <= acceptFileSize) {
callback(file);
return;
}
var img = new Image();
img.onerror = function() {
URL.revokeObjectURL(this.src);
callback(file);
};
img.onload = function() {
URL.revokeObjectURL(this.src);
getExifOrientation(file, function(orientation) {
var w = img.width, h = img.height;
var scale = (orientation > 4 ?
Math.min(maxHeight / w, maxWidth / h, 1) :
Math.min(maxWidth / w, maxHeight / h, 1));
h = Math.round(h * scale);
w = Math.round(w * scale);
var canvas = imgToCanvasWithOrientation(img, w, h, orientation);
canvas.toBlob(function(blob) {
console.log("Resized image to " + w + "x" + h + ", " + (blob.size >> 10) + "kB");
callback(blob);
}, 'image/jpeg', quality);
});
};
img.src = URL.createObjectURL(file);
}
Example usage:
inputfile.onchange = function() {
// If file size > 500kB, resize such that width <= 1000, quality = 0.9
reduceFileSize(this.files[0], 500*1024, 1000, Infinity, 0.9, blob => {
let body = new FormData();
body.set('file', blob, blob.name || "file.jpg");
fetch('/upload-image', {method: 'POST', body}).then(...);
});
};
#PsychoWoods' answer is good. I would like to offer my own solution. This Javascript function takes an image data URL and a width, scales it to the new width, and returns a new data URL.
// Take an image URL, downscale it to the given width, and return a new image URL.
function downscaleImage(dataUrl, newWidth, imageType, imageArguments) {
"use strict";
var image, oldWidth, oldHeight, newHeight, canvas, ctx, newDataUrl;
// Provide default values
imageType = imageType || "image/jpeg";
imageArguments = imageArguments || 0.7;
// Create a temporary image so that we can compute the height of the downscaled image.
image = new Image();
image.src = dataUrl;
oldWidth = image.width;
oldHeight = image.height;
newHeight = Math.floor(oldHeight / oldWidth * newWidth)
// Create a temporary canvas to draw the downscaled image on.
canvas = document.createElement("canvas");
canvas.width = newWidth;
canvas.height = newHeight;
// Draw the downscaled image on the canvas and return the new data URL.
ctx = canvas.getContext("2d");
ctx.drawImage(image, 0, 0, newWidth, newHeight);
newDataUrl = canvas.toDataURL(imageType, imageArguments);
return newDataUrl;
}
This code can be used anywhere you have a data URL and want a data URL for a downscaled image.
You can take a look at image-conversion,Try it here --> demo page
Try this Customizable Pure JS Sample - Compress over 90% :
<div id="root">
<p>Upload an image and see the result</p>
<input id="img-input" type="file" accept="image/*" style="display:block" />
</div>
<script>
const MAX_WIDTH = 320;
const MAX_HEIGHT = 180;
const MIME_TYPE = "image/jpeg";
const QUALITY = 0.7;
const input = document.getElementById("img-input");
input.onchange = function (ev) {
const file = ev.target.files[0]; // get the file
const blobURL = URL.createObjectURL(file);
const img = new Image();
img.src = blobURL;
img.onerror = function () {
URL.revokeObjectURL(this.src);
// Handle the failure properly
console.log("Cannot load image");
};
img.onload = function () {
URL.revokeObjectURL(this.src);
const [newWidth, newHeight] = calculateSize(img, MAX_WIDTH, MAX_HEIGHT);
const canvas = document.createElement("canvas");
canvas.width = newWidth;
canvas.height = newHeight;
const ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, newWidth, newHeight);
canvas.toBlob(
(blob) => {
// Handle the compressed image. es. upload or save in local state
displayInfo('Original file', file);
displayInfo('Compressed file', blob);
},
MIME_TYPE,
QUALITY
);
document.getElementById("root").append(canvas);
};
};
function calculateSize(img, maxWidth, maxHeight) {
let width = img.width;
let height = img.height;
// calculate the width and height, constraining the proportions
if (width > height) {
if (width > maxWidth) {
height = Math.round((height * maxWidth) / width);
width = maxWidth;
}
} else {
if (height > maxHeight) {
width = Math.round((width * maxHeight) / height);
height = maxHeight;
}
}
return [width, height];
}
// Utility functions for demo purpose
function displayInfo(label, file) {
const p = document.createElement('p');
p.innerText = `${label} - ${readableBytes(file.size)}`;
document.getElementById('root').append(p);
}
function readableBytes(bytes) {
const i = Math.floor(Math.log(bytes) / Math.log(1024)),
sizes = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
return (bytes / Math.pow(1024, i)).toFixed(2) + ' ' + sizes[i];
}
</script>
I find that there's simpler solution compared to the accepted answer.
Read the files using the HTML5 FileReader API with .readAsArrayBuffer
Create a Blob with the file data and get its url with window.URL.createObjectURL(blob)
Create new Image element and set it's src to the file blob url
Send the image to the canvas. The canvas size is set to desired output size
Get the scaled-down data back from canvas via canvas.toDataURL("image/jpeg",0.7) (set your own output format and quality)
Attach new hidden inputs to the original form and transfer the dataURI images basically as normal text
On backend, read the dataURI, decode from Base64, and save it
As per your question:
Is there a way to compress an image (mostly jpeg, png and gif)
directly browser-side, before uploading it
My solution:
Create a blob with the file directly with URL.createObjectURL(inputFileElement.files[0]).
Same as accepted answer.
Same as accepted answer. Worth mentioning that, canvas size is necessary and use img.width and img.height to set canvas.width and canvas.height. Not img.clientWidth.
Get the scale-down image by canvas.toBlob(callbackfunction(blob){}, 'image/jpeg', 0.5). Setting 'image/jpg' has no effect. image/png is also supported. Make a new File object inside the callbackfunction body with let compressedImageBlob = new File([blob]).
Add new hidden inputs or send via javascript . Server doesn't have to decode anything.
Check https://javascript.info/binary for all information. I came up the solution after reading this chapter.
Code:
<!DOCTYPE html>
<html>
<body>
<form action="upload.php" method="post" enctype="multipart/form-data">
Select image to upload:
<input type="file" name="fileToUpload" id="fileToUpload" multiple>
<input type="submit" value="Upload Image" name="submit">
</form>
</body>
</html>
This code looks far less scary than the other answers..
Update:
One has to put everything inside img.onload. Otherwise canvas will not be able to get the image's width and height correctly as the time canvas is assigned.
function upload(){
var f = fileToUpload.files[0];
var fileName = f.name.split('.')[0];
var img = new Image();
img.src = URL.createObjectURL(f);
img.onload = function(){
var canvas = document.createElement('canvas');
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
canvas.toBlob(function(blob){
console.info(blob.size);
var f2 = new File([blob], fileName + ".jpeg");
var xhr = new XMLHttpRequest();
var form = new FormData();
form.append("fileToUpload", f2);
xhr.open("POST", "upload.php");
xhr.send(form);
}, 'image/jpeg', 0.5);
}
}
3.4MB .png file compression test with image/jpeg argument set.
|0.9| 777KB |
|0.8| 383KB |
|0.7| 301KB |
|0.6| 251KB |
|0.5| 219kB |
I had an issue with the downscaleImage() function posted above by #daniel-allen-langdon in that the image.width and image.height properties are not available immediately because the image load is asynchronous.
Please see updated TypeScript example below that takes this into account, uses async functions, and resizes the image based on the longest dimension rather than just the width
function getImage(dataUrl: string): Promise<HTMLImageElement>
{
return new Promise((resolve, reject) => {
const image = new Image();
image.src = dataUrl;
image.onload = () => {
resolve(image);
};
image.onerror = (el: any, err: ErrorEvent) => {
reject(err.error);
};
});
}
export async function downscaleImage(
dataUrl: string,
imageType: string, // e.g. 'image/jpeg'
resolution: number, // max width/height in pixels
quality: number // e.g. 0.9 = 90% quality
): Promise<string> {
// Create a temporary image so that we can compute the height of the image.
const image = await getImage(dataUrl);
const oldWidth = image.naturalWidth;
const oldHeight = image.naturalHeight;
console.log('dims', oldWidth, oldHeight);
const longestDimension = oldWidth > oldHeight ? 'width' : 'height';
const currentRes = longestDimension == 'width' ? oldWidth : oldHeight;
console.log('longest dim', longestDimension, currentRes);
if (currentRes > resolution) {
console.log('need to resize...');
// Calculate new dimensions
const newSize = longestDimension == 'width'
? Math.floor(oldHeight / oldWidth * resolution)
: Math.floor(oldWidth / oldHeight * resolution);
const newWidth = longestDimension == 'width' ? resolution : newSize;
const newHeight = longestDimension == 'height' ? resolution : newSize;
console.log('new width / height', newWidth, newHeight);
// Create a temporary canvas to draw the downscaled image on.
const canvas = document.createElement('canvas');
canvas.width = newWidth;
canvas.height = newHeight;
// Draw the downscaled image on the canvas and return the new data URL.
const ctx = canvas.getContext('2d')!;
ctx.drawImage(image, 0, 0, newWidth, newHeight);
const newDataUrl = canvas.toDataURL(imageType, quality);
return newDataUrl;
}
else {
return dataUrl;
}
}
For Moderm browser use createImageBitmap() instead of img.onload
async function compressImage(blobImg, percent) {
let bitmap = await createImageBitmap(blobImg);
let canvas = document.createElement("canvas");
let ctx = canvas.getContext("2d");
canvas.width = bitmap.width;
canvas.height = bitmap.height;
ctx.drawImage(bitmap, 0, 0);
let dataUrl = canvas.toDataURL("image/jpeg", percent/100);
return dataUrl;
}
inputImg.addEventListener('change', async(e) => {
let img = e.target.files[0];
console.log('File Name: ', img.name)
console.log('Original Size: ', img.size.toLocaleString())
let imgCompressed = await compressImage(img, 75) // set to 75%
let compSize = atob(imgCompressed.split(",")[1]).length;
console.log('Compressed Size: ', compSize.toLocaleString())
//console.log(imgCompressed)
})
<input type="file" id="inputImg">
Edit: As per the Mr Me comment on this answer, it looks like compression is now available for JPG/WebP formats ( see https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL ).
As far as I know, you cannot compress images using canvas, instead, you can resize it. Using canvas.toDataURL will not let you choose the compression ratio to use. You can take a look at canimage that does exactly what you want : https://github.com/nfroidure/CanImage/blob/master/chrome/canimage/content/canimage.js
In fact, it's often sufficient to just resize the image to decrease it's size but if you want to go further, you'll have to use newly introduced method file.readAsArrayBuffer to get a buffer containing the image data.
Then, just use a DataView to read it's content according to the image format specification (http://en.wikipedia.org/wiki/JPEG or http://en.wikipedia.org/wiki/Portable_Network_Graphics).
It'll be hard to deal with image data compression, but it is worse a try. On the other hand, you can try to delete the PNG headers or the JPEG exif data to make your image smaller, it should be easier to do so.
You'll have to create another DataWiew on another buffer and fill it with the filtered image content. Then, you'll just have to encode you're image content to DataURI using window.btoa.
Let me know if you implement something similar, will be interesting to go through the code.
Compressor.js
https://github.com/fengyuanchen/compressorjs
import axios from 'axios';
import Compressor from 'compressorjs';
document.getElementById('file').addEventListener('change', (e) => {
const file = e.target.files[0];
if (!file) {
return;
}
new Compressor(file, {
quality: 0.6,
// The compression process is asynchronous,
// which means you have to access the `result` in the `success` hook function.
success(result) {
const formData = new FormData();
// The third parameter is required for server
formData.append('file', result, result.name);
// Send the compressed image file to server with XMLHttpRequest.
axios.post('/path/to/upload', formData).then(() => {
console.log('Upload success');
});
},
error(err) {
console.log(err.message);
},
});
});
I used the following package:
https://www.npmjs.com/package/browser-image-compression
npm install browser-image-compression
or
yarn add browser-image-compression
Then just following the docs:
import imageCompression from 'browser-image-compression';
const options = {
maxSizeMB: 0.5, // pretty much self-explanatory
maxWidthOrHeight: 500, // apparently px
}
imageCompression(file, options)
.then(function(compressedFile) {
console.log(
"compressedFile instanceof Blob",
compressedFile instanceof Blob
); // true
console.log(
`compressedFile size ${compressedFile.size /
1024 /
1024} MB`
); // smaller than maxSizeMB
return uploader(compressedFile); // code to actual upload, in my case uploader() is a function to upload to Firebase storage.
})
Just in case if you were curios about the uploader(), here's the code of it:
import { initializeApp } from "firebase/app";
const firebaseConfig = {
// your config
};
initializeApp(firebaseConfig);
import { getStorage, ref, uploadBytes, getDownloadURL } from "firebase/storage";
const storage = getStorage();
const sRef = ref(storage);
const uploader = async (file) => {
/* uploads to root */
// const imageRef = ref(sRef, file.name);
// console.log(imageRef);
// await uploadBytes(imageRef, file).then((snapshot) => {
// console.log("Uploaded a blob or file!", snapshot);
// });
/* upload to folder 'techs/' */
const folderRef = ref(sRef, "techs/" + file.name);
await uploadBytes(folderRef, file);
// get URL
const url = await getDownloadURL(ref(storage, folderRef));
console.log("url: ", url);
return url;
};
You can compress an image using the HTML <canvas> element:
function compressImage(imgToCompress, resizingFactor, quality) {
// resizing the image
const canvas = document.createElement("canvas");
const context = canvas.getContext("2d");
const originalWidth = imgToCompress.width;
const originalHeight = imgToCompress.height;
const canvasWidth = originalWidth * resizingFactor;
const canvasHeight = originalHeight * resizingFactor;
canvas.width = canvasWidth;
canvas.height = canvasHeight;
context.drawImage(
imgToCompress,
0,
0,
originalWidth * resizingFactor,
originalHeight * resizingFactor
);
// reducing the quality of the image
canvas.toBlob(
(blob) => {
if (blob) {
// showing the compressed image
resizedImage.src = URL.createObjectURL(resizedImageBlob);
}
},
"image/jpeg",
quality
);
}
See this blog post for an in depth explanation: https://img.ly/blog/how-to-compress-an-image-before-uploading-it-in-javascript/
i improved the function a head to be this :
var minifyImg = function(dataUrl,newWidth,imageType="image/jpeg",resolve,imageArguments=0.7){
var image, oldWidth, oldHeight, newHeight, canvas, ctx, newDataUrl;
(new Promise(function(resolve){
image = new Image(); image.src = dataUrl;
log(image);
resolve('Done : ');
})).then((d)=>{
oldWidth = image.width; oldHeight = image.height;
log([oldWidth,oldHeight]);
newHeight = Math.floor(oldHeight / oldWidth * newWidth);
log(d+' '+newHeight);
canvas = document.createElement("canvas");
canvas.width = newWidth; canvas.height = newHeight;
log(canvas);
ctx = canvas.getContext("2d");
ctx.drawImage(image, 0, 0, newWidth, newHeight);
//log(ctx);
newDataUrl = canvas.toDataURL(imageType, imageArguments);
resolve(newDataUrl);
});
};
the use of it :
minifyImg(<--DATAURL_HERE-->,<--new width-->,<--type like image/jpeg-->,(data)=>{
console.log(data); // the new DATAURL
});
enjoy ;)
For JPG Image compression you can use the best compression technique called JIC
(Javascript Image Compression)This will definitely help you -->https://github.com/brunobar79/J-I-C
I'm trying to add images to canvas strictly, but images are added randomly.
What's the problem?
Here is my simple code.
var canvas = new fabric.Canvas("preview");
var imgs = ['bgBottom','bgTop', 'bgLevel', 'bgCircle'];
for (var i=0; i<imgs.length;i++){
var url = imgs[i]+'.png';
fabric.Image.fromURL(url, function (oImg) {
canvas.add(oImg)
})
}
fabric.Image.fromURL loads the image in the background and runs the anonymous function you pass to it once image load is complete which adds it to the canvas. The order that the browser loads the images will vary and you can't rely on it being in a specific order.
Check out this jsfiddle that shows loading an array of images and making sure they're displayed in a set order. This works by adding the image to the canvas before it's loaded; it just doesn't render until the image is available to be displayed.
The code from the jsfiddle:
var SelfLoadingImage = fabric.util.createClass(fabric.Object, {
initialize: function(src) {
this.image = new Image();
this.image.src = src;
this.image.onload = (function() {
this.width = this.image.width;
this.height = this.image.height;
this.loaded = true;
this.setCoords();
this.fire('image:loaded');
canvas.renderAll();
}).bind(this);
},
_render: function(ctx)
{
if (this.loaded) {
ctx.drawImage(this.image, -this.width / 2, -this.height / 2);
}
}
});
var canvas = new fabric.Canvas("preview");
var imgs = [
'http://icons.iconarchive.com/icons/fasticon/ifunny/128/dog-icon.png', // dog
'http://33.media.tumblr.com/avatar_14ee6ada72a4_128.png', // cat
'http://upload.wikimedia.org/wikipedia/commons/b/bc/Nuvola_devices_mouse.png' // mouse
];
for (var i=0; i<imgs.length;i++){
var url = imgs[i];
var img = new SelfLoadingImage(url);
canvas.add(img);
}