I'm a server-side dev learning the ropes of vanilla JS. I need to clear my concepts regarding sending an Ajax POST request for an image object I'm creating in JS - this question is about that.
Imagine a web app where users upload photos for others to see. At the point of each image's upload, I use vanilla JS to confirm the image's mime-type (via interpreting magic numbers), and then resize the image for optimization purposes.
After resizing, I do:
var canvas = document.createElement('canvas');
canvas.width = resized_width;
canvas.height = resized_height;
var ctx = canvas.getContext("2d");
ctx.drawImage(source_img, 0, 0, resized_width, resized_height);
var resized_img = new Image();
resized_img.src = canvas.toDataURL("image/jpeg",0.7);
return resized_img;
The image object returned has to be sent to the backend via an Ajax request. Something like:
function overwrite_default_submit(e) {
e.preventDefault();
var form = new FormData();
form.append("myfile", resized_img, img_name);
var xhr = new XMLHttpRequest();
xhr.open('POST', e.target.action);
// xhr.send(form); // uncomment to really send the request
}
However, the image object returned after resizing is essentially an HTML element like so <img src="data:image/jpeg;base64>. Whereas the object expected in the FormData object ought to be a File object, e.g. something like: File { name: "example.jpg", lastModified: 1500117303000, lastModifiedDate: Date 2017-07-15T11:15:03.000Z, webkitRelativePath: "", size: 115711, type: "image/jpeg" }.
So what do I do to fix this issue? Would prefer to learn the most efficient way of doing things here.
Btw, I've seen an example on SO of using the JS FILE object, but I'd prefer a more cross-browser method, given File garnered support from Safari, Opera Mobile and built-in Android browsers relatively recently.
Moreover, only want pure JS solutions since I'm using this as an exercise to learn the ropes. JQuery is on my radar, but for later.
The rest of my code is as follows (only included JPEG processing for brevity):
var max_img_width = 400;
var wranges = [max_img_width, Math.round(0.8*max_img_width), Math.round(0.6*max_img_width),Math.round(0.4*max_img_width),Math.round(0.2*max_img_width)];
// grab the file from the input and process it
function process_user_file(e) {
var file = e.target.files[0];
var reader = new FileReader();
reader.onload = process_image;
reader.readAsArrayBuffer(file.slice(0,25));
}
// checking file type programmatically (via magic numbers), getting dimensions and returning a compressed image
function process_image(e) {
var img_width;
var img_height;
var view = new Uint8Array(e.target.result);
var arr = view.subarray(0, 4);
var header = "";
for(var i = 0; i < arr.length; i++) {
header += arr[i].toString(16);
}
switch (header) {
case "ffd8ffe0":
case "ffd8ffe1":
case "ffd8ffe2":
case "ffd8ffe3":
case "ffd8ffe8":
// magic numbers represent type = "image/jpeg";
// use the 'slow' method to get the dimensions of the media
img_file = browse_image_btn.files[0];
var fr = new FileReader();
fr.onload = function(){
var dataURL = fr.result;
var img = new Image();
img.onload = function() {
img_width = this.width;
img_height = this.height;
resized_img = resize_and_compress(this, img_width, img_height, 80);
}
img.src = dataURL;
};
fr.readAsDataURL(img_file);
to_send = browse_image_btn.files[0];
load_rest = true;
subform.disabled = false;
break;
default:
// type = "unknown"; // Or one can use the blob.type as fallback
load_rest = false;
subform.disabled = true;
browse_image_btn.value = "";
to_send = null;
break;
}
}
// resizing (& compressing) image
function resize_and_compress(source_img, img_width, img_height, quality){
var new_width;
switch (true) {
case img_width < wranges[4]:
new_width = wranges[4];
break;
case img_width < wranges[3]:
new_width = wranges[4];
break;
case img_width < wranges[2]:
new_width = wranges[3];
break;
case img_width < wranges[1]:
new_width = wranges[2];
break;
case img_width < wranges[0]:
new_width = wranges[1];
break;
default:
new_width = wranges[0];
break;
}
var wpercent = (new_width/img_width);
var new_height = Math.round(img_height*wpercent);
var canvas = document.createElement('canvas');
canvas.width = new_width;
canvas.height = new_height;
var ctx = canvas.getContext("2d");
ctx.drawImage(source_img, 0, 0, new_width, new_height);
console.log(ctx);
var resized_img = new Image();
resized_img.src = canvas.toDataURL("image/jpeg",quality/100);
return resized_img;
}
Update: I'm employing the following:
// converting image data uri to a blob object
function dataURItoBlob(dataURI,mime_type) {
var byteString = atob(dataURI.split(',')[1]);
var ab = new ArrayBuffer(byteString.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < byteString.length; i++) { ia[i] = byteString.charCodeAt(i); }
return new Blob([ab], { type: mime_type });
}
Where the dataURI parameter is canvas.toDataURL(mime_type,quality/100)
You should call the canvas.toBlob() to get the binary instead of using a base64 string.
it's async so you would have to add a callback to it.
canvas.toBlob(function(blob) {
resized_img.onload = function() {
// no longer need to read the blob so it's revoked
URL.revokeObjectURL(this.url);
};
// Preview the image using createObjectURL
resized_img.src = URL.createObjectURL(blob);
// Attach the blob to the FormData
var form = new FormData();
form.append("myfile", blob, img_name);
}, "image/jpeg", 0.7);
See to this SO post: How to get base64 encoded data from html image
I think you need to call 'canvas.toDataURL()' to get the actual base64 stream of the image.
var image = canvas.toDataURL();
Then upload it with a Form: Upload a base64 encoded image using FormData?
var data = new FormData();
data.append("image_data", image);
Untested, but this should be about it.
Related
I am trying to generate a pdf report including current map screenshot of ESRI map using JavaScript. Here is my code.
var getCurrentMapScreenShot = function (success, error) {
esriLoader.Config.defaults.io.proxyUrl = myAppSettingsModel.SettingsModel.MapSettings.AGSProxyURL;
esriLoader.Config.defaults.io.alwaysUseProxy = true;
var printTask = new esriLoader.PrintTask("myexportUrl");
var template = new esriLoader.PrintTemplate();
template.exportOptions = {
width: 600,
height: 600,
dpi: 96
};
template.format = "image/png";
template.layout = "MAP_ONLY",
template.preserveScale = true;
template.layoutOptions = {
legendLayers: [], // empty array means no legend
scalebarUnit: "Miles"
};
var params = new esriLoader.PrintParameters();
params.map = map;
params.template = template;
printTask.execute(params, success, error);
}
This function will give you an event that contains a url , Then I am passing this url to get map base64 data.
Here is the function calling.
map.GetCurrentMapScreenShot(function (event) {
var mapScreenShotURL = event.url;
Factory.GetBase64ForImgUrl(mapScreenShotURL,
function (mapImageBase64Encoded) {});
and here is the function that converts url to base64image
function getBase64ForImgUrl(url, callback, outputFormat) {
console.log("#################### Summary Report Image " + url);
var canvas = document.createElement('CANVAS');
var ctx = canvas.getContext('2d');
var img = new Image;
img.crossOrigin = 'Anonymous';
img.onload = function () {
canvas.height = img.height;
canvas.width = img.width;
ctx.drawImage(img, 0, 0);
var dataURL = canvas.toDataURL(outputFormat || 'image/png');
callback.call(this, dataURL);
// Clean up
canvas = null;
};
img.src = url;
}
I am getting base64 image data of the map , But the problem is that, I am getting blurred image of the map with no feature layers and no icons..And also map contains some junk texts.
Thanks
I resolved the issue almost, Now I am getting the map image that contains map Icons and layer graphics, But unfortunately still getting some junk texts.
I have changed the code as follows.
template.format = "JPG";
template.layout = "A4 Landscape",
template.preserveScale = false;
template.layoutOptions = {
"legendLayers": [], // empty array means no legend
"scalebarUnit": "Miles"
}
i've image uploader which using canvas and trying to get orientation using load-image.all.min.js is fine. but when i choose multiple image orientation parsing function saving data not one by one.
which means if i choose 1 image. it transferring data to 'upload_canvas.php?ori='+ori with correct ori variable.
but when i choose multiple image to upload example 3 images (with orientation 1, 1, 8)
it passing data to server upload_canvas.php?ori=8, upload_canvas.php?ori=8, upload_canvas.php?ori=8. only last ori variable.
maybe orientation parsing function already looped before uploading image data to server one by one.
how to transfer image with correct orientation to server?
below my using code.
document.querySelector('form input[type=file]').addEventListener('change', function(event){
// Read files
var files = event.target.files;
var ori = 1;
// Iterate through files
for (var i = 0; i < files.length; i++) {
// Ensure it's an image
if (files[i].type.match(/image.*/)) {
//Get image orienatation
loadImage.parseMetaData(files[i], function (data) {
if (data.exif) {
ori = data.exif.get('Orientation');
console.log("ori: "+ori);
} else {ori = 1;}
});
// Load image
var reader = new FileReader();
reader.onload = function (readerEvent) {
var image = new Image();
image.onload = function (imageEvent) {
canvas.width = image.width;
canvas.height = image.height;
drawImageIOSFix(canvas.getContext('2d'),image, 0, 0, image.width, image.height, 0, 0, width, height);
// Upload image
var xhr = new XMLHttpRequest();
if (xhr.upload) {
// Update progress
xhr.upload.addEventListener('progress', function(event) {
var percent = parseInt(event.loaded / event.total * 100);
progressElement.style.width = percent+'%';
}, false);
// File uploaded / failed
xhr.onreadystatechange = function(event) {
if (xhr.readyState == 4) {
if (xhr.status == 200) {
//some code
} else {
imageElement.parentNode.removeChild(imageElement);
}
}
}
xhr.open('post', 'upload_canvas.php?t=' + Math.random()+'&ori='+ori, true);
xhr.send(canvas.toDataURL('image/jpeg'));
}
}
image.src = readerEvent.target.result;
}
reader.readAsDataURL(files[i]);
}
}
// Clear files
event.target.value = '';});
Your variable ori is a global variable, that is shared between all images. The code in the .onload functions aren't run immediately, but only after your for() loop has gone through all the images. At this point ori will contain the orientation of the last image.
To fix, move the variable and parseMetaData into the reader.onload function.
...
var reader = new FileReader();
reader.onload = function (readerEvent) {
var ori;
loadImage.parseMetaData(files[i], ...)
var image = new Image();
image.onload = function (imageEvent) {
...
Warning: Not tested!
How can I strip the EXIF data from an uploaded image through javascript? I am currently able to access the EXIF data using this exif-js plugin, like this:
EXIF.getData(oimg, function() {
var orientation = EXIF.getTag(this, "Orientation");
});
However, I have not found any way to actually remove the Exif data, only to retrieve it.
More specifically, I am trying to do this to get rid of the orientation Exif data which rotates my image on certain browsers.
look up the file format and exif format
read the file into arraybuffer
find the required data and remove it
create a blob from the remaining data
upload it with ajax
Here is a little demo of it, select an image with orientation data to see how it looks with and with out it(modern browsers only).
http://jsfiddle.net/mowglisanu/frhwm2xe/3/
var input = document.querySelector('#erd');
input.addEventListener('change', load);
function load(){
var fr = new FileReader();
fr.onload = process;
fr.readAsArrayBuffer(this.files[0]);
document.querySelector('#orig').src = URL.createObjectURL(this.files[0]);
}
function process(){
var dv = new DataView(this.result);
var offset = 0, recess = 0;
var pieces = [];
var i = 0;
if (dv.getUint16(offset) == 0xffd8){
offset += 2;
var app1 = dv.getUint16(offset);
offset += 2;
while (offset < dv.byteLength){
//console.log(offset, '0x'+app1.toString(16), recess);
if (app1 == 0xffe1){
pieces[i] = {recess:recess,offset:offset-2};
recess = offset + dv.getUint16(offset);
i++;
}
else if (app1 == 0xffda){
break;
}
offset += dv.getUint16(offset);
var app1 = dv.getUint16(offset);
offset += 2;
}
if (pieces.length > 0){
var newPieces = [];
pieces.forEach(function(v){
newPieces.push(this.result.slice(v.recess, v.offset));
}, this);
newPieces.push(this.result.slice(recess));
var br = new Blob(newPieces, {type: 'image/jpeg'});
document.querySelector('#mod').src = URL.createObjectURL(br);
}
}
}
img{
max-width:200px;
}
<input id="erd" type="file"/><br>
<img id="orig" title="Original">
<img id="mod" title="Modified">
Am working on a winjs based barcode reader application. Initially I will capture the image using camera capture API and will pass that file object to a canvas element and read its barcode using ZXing library. But the image passed to the canvas is not getting rendered completely as follows.
Following is my html code
<body>
<p>Decoding test for static images</p>
<canvas id="canvasDecode" height="200" width="200"></canvas>
<h3 id="result"></h3>
<p>Put some content here and leave the text box</p>
<input id="input" class="win-textarea" onchange="generate_barcode()">
<h3 id="content"></h3>
<canvas id="canvasEncode" height="200" width="200"></canvas>
<img class="imageHolder" id="capturedPhoto" alt="image holder" />
</body>
following is my javascript code
(function () {
"use strict";
WinJS.Binding.optimizeBindingReferences = true;
var app = WinJS.Application;
var activation = Windows.ApplicationModel.Activation;
app.onactivated = function (args) {
if (args.detail.kind === activation.ActivationKind.launch) {
if (args.detail.previousExecutionState !== activation.ApplicationExecutionState.terminated) {
// TODO: This application has been newly launched. Initialize
// your application here.
var dialog = new Windows.Media.Capture.CameraCaptureUI();
var aspectRatio = { width: 1, height: 1 };
dialog.photoSettings.croppedAspectRatio = aspectRatio;
dialog.captureFileAsync(Windows.Media.Capture.CameraCaptureUIMode.photo).then(function (file) {
if (file) {
// draw the image
var canvas = document.getElementById('canvasDecode')
var ctx = canvas.getContext('2d');
var img = new Image;
img.onload = function () {
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0, img.width, img.height);
}
img.src = URL.createObjectURL(file);
// open a stream from the image
return file.openAsync(Windows.Storage.FileAccessMode.readWrite);
}
})
.then(function (stream) {
if (stream) {
// create a decoder from the image stream
return Windows.Graphics.Imaging.BitmapDecoder.createAsync(stream);
}
})
.done(function (decoder) {
if (decoder) {
// get the raw pixel data from the decoder
decoder.getPixelDataAsync().then(function (pixelDataProvider) {
var rawPixels = pixelDataProvider.detachPixelData();
var pixels, format; // Assign these in the below switch block.
switch (decoder.bitmapPixelFormat) {
case Windows.Graphics.Imaging.BitmapPixelFormat.rgba16:
// Allocate a typed array with the raw pixel data
var pixelBufferView_U8 = new Uint8Array(rawPixels);
// Uint16Array provides a typed view into the raw 8 bit pixel data.
pixels = new Uint16Array(pixelBufferView_U8.buffer);
if (decoder.bitmapAlphaMode == Windows.Graphics.Imaging.BitmapAlphaMode.straight)
format = ZXing.BitmapFormat.rgba32;
else
format = ZXing.BitmapFormat.rgb32;
break;
case Windows.Graphics.Imaging.BitmapPixelFormat.rgba8:
// For 8 bit pixel formats, just use the returned pixel array.
pixels = rawPixels;
if (decoder.bitmapAlphaMode == Windows.Graphics.Imaging.BitmapAlphaMode.straight)
format = ZXing.BitmapFormat.rgba32;
else
format = ZXing.BitmapFormat.rgb32;
break;
case Windows.Graphics.Imaging.BitmapPixelFormat.bgra8:
// For 8 bit pixel formats, just use the returned pixel array.
pixels = rawPixels;
if (decoder.bitmapAlphaMode == Windows.Graphics.Imaging.BitmapAlphaMode.straight)
format = ZXing.BitmapFormat.bgra32;
else
format = ZXing.BitmapFormat.bgr32;
break;
}
// create a barcode reader
var reader = new ZXing.BarcodeReader();
reader.onresultpointfound = function (resultPoint) {
// do something with the resultpoint location
}
// try to decode the raw pixel data
var result = reader.decode(pixels, decoder.pixelWidth, decoder.pixelHeight, format);
// show the result
if (result) {
document.getElementById("result").innerText = result.text;
}
else {
document.getElementById("result").innerText = "no barcode found";
}
});
}
});
} else {
// TODO: This application has been reactivated from suspension.
// Restore application state here.
}
args.setPromise(WinJS.UI.processAll());
}
};
app.oncheckpoint = function (args) {
// TODO: This application is about to be suspended. Save any state
// that needs to persist across suspensions here. You might use the
// WinJS.Application.sessionState object, which is automatically
// saved and restored across suspension. If you need to complete an
// asynchronous operation before your application is suspended, call
// args.setPromise().
};
app.start();
})();
function generate_barcode() {
// get the content which the user puts into the textbox
var content = document.getElementById("input").value;
// create the barcode writer and set some options
var writer = new ZXing.BarcodeWriter();
writer.options = new ZXing.Common.EncodingOptions();
writer.options.height = 200;
writer.options.width = 200;
writer.format = ZXing.BarcodeFormat.qr_CODE;
// encode the content to a byte array with 4 byte per pixel as BGRA
var imagePixelData = writer.write(content);
// draw the pixel data to the canvas
var ctx = document.getElementById('canvasEncode').getContext('2d');
var imageData = ctx.createImageData(imagePixelData.width, imagePixelData.heigth);
var pixel = imagePixelData.pixel
for (var index = 0; index < pixel.length; index++) {
imageData.data[index] = pixel[index];
}
ctx.putImageData(imageData, 0, 0);
}
The same code worked well when I was using the file picker API. Let me knew where I went wrong.
I think that you're running into some problems with asynchronicity here. I applaud your use of chained calls to then(), but there's a hidden problem - assignment to img.src begins an asynchronous operation while the image is loaded. Your code continues on BEFORE the img.onload event has been raised, and so the closure which img.onload reaches into for the img variable (the pointer to the file URL) changes before the image has fully loaded.
Here's some code that worked for me.
// Inside handler for app.activated ...
var dialog = new Windows.Media.Capture.CameraCaptureUI();
var aspectRatio = { width: 1, height: 1 };
dialog.photoSettings.croppedAspectRatio = aspectRatio;
dialog.captureFileAsync(Windows.Media.Capture.CameraCaptureUIMode.photo)
.then(function (file) {
// draw the image
var canvas = document.getElementById('canvasDecode')
var ctx = canvas.getContext('2d');
var img = new Image;
img.onload = function () {
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0, img.width, img.height);
// open a stream from the image
decodePic(file);
}
img.onerror = function (err) {
WinJS.log && WinJS.log("Error loading image");
}
img.src = URL.createObjectURL(file);
});
And then I moved the file decoding / barcode reading stuff to a new function.
function decodePic(file) {
file.openAsync(Windows.Storage.FileAccessMode.readWrite)
.then(function (stream) {
if (stream) {
// create a decoder from the image stream
return Windows.Graphics.Imaging.BitmapDecoder.createAsync(stream);
}
})
.done(function (decoder) {
if (decoder) {
// get the raw pixel data from the decoder
decoder.getPixelDataAsync().then(function (pixelDataProvider) {
// YOUR BARCODE READING CODE HERE.
});
}
});
}
I hope this helps!
The below handleFiles method is being passed files from both drag and drop and a file input. After it gets the data url for a given file it passes it to the processImage function. This function creates a new image and sets the src and file for that image. I then take different actions based on the width of the incoming image and insert the image into the dom. However, I noticed when dropping in a bunch of images imageWidth will get set to 0. I have confirmed the image.src is correctly set and that dropping the same image in by itself works fine. I also have confirmed that if I remove the width calculations the image does display correctly on the page. When I enter the debugger I can confirm that immediately after imageWidth is set to 0 i.width returns a correct value. At first I thought it might be a threading issue in Chrome, but then when I saw it happen in FireFox as well I became alarmed. I have not been able to pinpoint a certain threshold, but the more load you put on the browser the less likely it is to correctly get the width.
I am seeing the problem in both FireFox 16.0.2 and Chrome 23.0.1271.95.
function handleFiles(files) {
for (var i = 0; i < files.length; i++) {
var file = files[i];
if( !isImage(file) ) {
continue;
}
var reader = new FileReader();
reader.onloadend = function(e) {
var dataURL = e.target.result;
processImage(file, dataURL);
}
reader.readAsDataURL(file);
}
}
function processImage(file, dataURL) {
var i = new Image();
i.src = dataURL;
i.file = file;
//console.log(i);
var maxWidth = 600;
var imageWidth = i.width;
......
}
As with all images, they may need time to load before they will tell you their width:
var i = new Image();
i.onload = function() {
//console.log(i);
var maxWidth = 600;
var imageWidth = this.width;
}
i.src = dataURL;
i.file = file;
The width (and height) might be 0 because it's not loaded yet.
Try adding the load event like so:
function processImage(file, dataURL) {
var i = new Image();
i.addEventListener("load", function () {
var maxWidth = 600;
var imageWidth = i.width;
......
});
i.src = dataURL;
i.file = file;
}