上传前获取文件大小，图像宽度和高度

Question

在使用jQuery或JavaScript上传到我的网站之前，如何获取文件大小，图像高度和宽度？

Answer 1

Multiple images upload with info data preview

Using HTML5 and the File API

Example using URL API

The images sources will be a URL representing the Blob object
<img src="blob:null/026cceb9-edr4-4281-babb-b56cbf759a3d">

 const EL_browse = document.getElementById('browse'); const EL_preview = document.getElementById('preview'); const readImage = file => { if ( !(/^image\\/(png|jpe?g|gif)$/).test(file.type) ) return EL_preview.insertAdjacentHTML('beforeend', `Unsupported format ${file.type}: ${file.name}<br>`); const img = new Image(); img.addEventListener('load', () => { EL_preview.appendChild(img); EL_preview.insertAdjacentHTML('beforeend', `<div>${file.name} ${img.width}×${img.height} ${file.type} ${Math.round(file.size/1024)}KB<div>`); window.URL.revokeObjectURL(img.src); // Free some memory }); img.src = window.URL.createObjectURL(file); } EL_browse.addEventListener('change', ev => { EL_preview.innerHTML = ''; // Remove old images and data const files = ev.target.files; if (!files || !files[0]) return alert('File upload not supported'); [...files].forEach( readImage ); }); 

 #preview img { max-height: 100px; } 

 <input id="browse" type="file" multiple> <div id="preview"></div> 

Example using FileReader API

In case you need images sources as long Base64 encoded data strings
<img src="data:image/png;base64,iVBORw0KGg... ...lF/++TkSuQmCC=">

 const EL_browse = document.getElementById('browse'); const EL_preview = document.getElementById('preview'); const readImage = file => { if ( !(/^image\\/(png|jpe?g|gif)$/).test(file.type) ) return EL_preview.insertAdjacentHTML('beforeend', `<div>Unsupported format ${file.type}: ${file.name}</div>`); const reader = new FileReader(); reader.addEventListener('load', () => { const img = new Image(); img.addEventListener('load', () => { EL_preview.appendChild(img); EL_preview.insertAdjacentHTML('beforeend', `<div>${file.name} ${img.width}×${img.height} ${file.type} ${Math.round(file.size/1024)}KB</div>`); }); img.src = reader.result; }); reader.readAsDataURL(file); }; EL_browse.addEventListener('change', ev => { EL_preview.innerHTML = ''; // Clear Preview const files = ev.target.files; if (!files || !files[0]) return alert('File upload not supported'); [...files].forEach( readImage ); }); 

 #preview img { max-height: 100px; } 

 <input id="browse" type="file" multiple> <div id="preview"></div> 

Answer 2

If you can use the jQuery validation plugin you can do it like so:

Html:

<input type="file" name="photo" id="photoInput" />

JavaScript:

$.validator.addMethod('imagedim', function(value, element, param) {
  var _URL = window.URL;
        var  img;
        if ((element = this.files[0])) {
            img = new Image();
            img.onload = function () {
                console.log("Width:" + this.width + "   Height: " + this.height);//this will give you image width and height and you can easily validate here....

                return this.width >= param
            };
            img.src = _URL.createObjectURL(element);
        }
});

The function is passed as ab onload function.

The code is taken from here

Answer 3

Demo

Not sure if it is what you want, but just simple example:

var input = document.getElementById('input');

input.addEventListener("change", function() {
    var file  = this.files[0];
    var img = new Image();

    img.onload = function() {
        var sizes = {
            width:this.width,
            height: this.height
        };
        URL.revokeObjectURL(this.src);

        console.log('onload: sizes', sizes);
        console.log('onload: this', this);
    }

    var objectURL = URL.createObjectURL(file);

    console.log('change: file', file);
    console.log('change: objectURL', objectURL);
    img.src = objectURL;
});

Answer 4

Here is a pure JavaScript example of picking an image file, displaying it, looping through the image properties, and then re-sizing the image from the canvas into an IMG tag and explicitly setting the re-sized image type to jpeg.

If you right click the top image, in the canvas tag, and choose Save File As, it will default to a PNG format. If you right click, and Save File as the lower image, it will default to a JPEG format. Any file over 400px in width is reduced to 400px in width, and a height proportional to the original file.

HTML

<form class='frmUpload'>
  <input name="picOneUpload" type="file" accept="image/*" onchange="picUpload(this.files[0])" >
</form>

<canvas id="cnvsForFormat" width="400" height="266" style="border:1px solid #c3c3c3"></canvas>
<div id='allImgProperties' style="display:inline"></div>

<div id='imgTwoForJPG'></div>

SCRIPT

<script>

window.picUpload = function(frmData) {
  console.log("picUpload ran: " + frmData);

var allObjtProperties = '';
for (objProprty in frmData) {
    console.log(objProprty + " : " + frmData[objProprty]);
    allObjtProperties = allObjtProperties + "<span>" + objProprty + ": " + frmData[objProprty] + ", </span>";
};

document.getElementById('allImgProperties').innerHTML = allObjtProperties;

var cnvs=document.getElementById("cnvsForFormat");
console.log("cnvs: " + cnvs);
var ctx=cnvs.getContext("2d");

var img = new Image;
img.src = URL.createObjectURL(frmData);

console.log('img: ' + img);

img.onload = function() {
  var picWidth = this.width;
  var picHeight = this.height;

  var wdthHghtRatio = picHeight/picWidth;
  console.log('wdthHghtRatio: ' + wdthHghtRatio);

  if (Number(picWidth) > 400) {
    var newHeight = Math.round(Number(400) * wdthHghtRatio);
  } else {
    return false;
  };

    document.getElementById('cnvsForFormat').height = newHeight;
    console.log('width: 400  h: ' + newHeight);
    //You must change the width and height settings in order to decrease the image size, but
    //it needs to be proportional to the original dimensions.
    console.log('This is BEFORE the DRAW IMAGE');
    ctx.drawImage(img,0,0, 400, newHeight);

    console.log('THIS IS AFTER THE DRAW IMAGE!');

    //Even if original image is jpeg, getting data out of the canvas will default to png if not specified
    var canvasToDtaUrl = cnvs.toDataURL("image/jpeg");
    //The type and size of the image in this new IMG tag will be JPEG, and possibly much smaller in size
    document.getElementById('imgTwoForJPG').innerHTML = "<img src='" + canvasToDtaUrl + "'>";
};
};

</script>

Here is a jsFiddle:

jsFiddle Pick, display, get properties, and Re-size an image file

In jsFiddle, right clicking the top image, which is a canvas, won't give you the same save options as right clicking the bottom image in an IMG tag.

Answer 5

So I started experimenting with the different things that FileReader API had to offer and could create an IMG tag with a DATA URL.

Drawback: It doesn't work on mobile phones, but it works fine on Google Chrome.

 $('input').change(function() { var fr = new FileReader; fr.onload = function() { var img = new Image; img.onload = function() { //I loaded the image and have complete control over all attributes, like width and src, which is the purpose of filereader. $.ajax({url: img.src, async: false, success: function(result){ $("#result").html("READING IMAGE, PLEASE WAIT...") $("#result").html("<img src='" + img.src + "' />"); console.log("Finished reading Image"); }}); }; img.src = fr.result; }; fr.readAsDataURL(this.files[0]); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <input type="file" accept="image/*" capture="camera"> <div id='result'>Please choose a file to view it. <br/>(Tested successfully on Chrome - 100% SUCCESS RATE)</div> 

(see this on a jsfiddle at http://jsfiddle.net/eD2Ez/530/ )
(see the original jsfiddle that i added upon to at http://jsfiddle.net/eD2Ez/ )

Answer 6

As far as I know there is not an easy way to do this since Javascript/JQuery does not have access to the local filesystem. There are some new features in html 5 that allows you to check certain meta data such as file size but I'm not sure if you can actually get the image dimensions.

Here is an article I found regarding the html 5 features, and a work around for IE that involves using an ActiveX control. http://jquerybyexample.blogspot.com/2012/03/how-to-check-file-size-before-uploading.html

Answer 7

A working jQuery validate example:

   $(function () {
        $('input[type=file]').on('change', function() {
            var $el = $(this);
            var files = this.files;
            var image = new Image();
            image.onload = function() {
                $el
                    .attr('data-upload-width', this.naturalWidth)
                    .attr('data-upload-height', this.naturalHeight);
            }

            image.src = URL.createObjectURL(files[0]);
        });

        jQuery.validator.unobtrusive.adapters.add('imageminwidth', ['imageminwidth'], function (options) {
            var params = {
                imageminwidth: options.params.imageminwidth.split(',')
            };

            options.rules['imageminwidth'] = params;
            if (options.message) {
                options.messages['imageminwidth'] = options.message;
            }
        });

        jQuery.validator.addMethod("imageminwidth", function (value, element, param) {
            var $el = $(element);
            if(!element.files && element.files[0]) return true;
            return parseInt($el.attr('data-upload-width')) >=  parseInt(param["imageminwidth"][0]);
        });

    } (jQuery));