Develop Reference

Display image after file input selection with image resize

I have seen posts asking how to display an image selected via a file input control. When I try these solutions, they work, yet I have a further issue I am unable to discover an answer to on my own: When I select an image for the first time, the image will not display because no image width and height data is available (image data is available via the FileReader obj, yet not the image width and height). The second time the image is selected (or after a reload), the width and height become available. Why is this occurring and what can I do to fix it? thanks.
Here's some code I've been using - this is one of the FileReader functions. I started by using reader.onload, but then thought the image width and height were not available because it hadn't loaded fully yet. Therefore onloadend seemed a better choice. It doesn't work any better here, though:
reader.onloadend = function(e) {
var img = new Image();
img.src = e.target.result;// or reader.result - doesn't matter
// A function that does math to proportionally scale the image
var new_size = scaleImageSize(150, 150, img.width, img.height);
img.width = new_size[0];
img.height = new_size[1];
// And here I am trying both ways to display the image: the first
// in a div tag, the second straight into an img tag. I only want
// to use one of these - preferably the div tag. I have also tried
// drawing the image onto an HTML5 canvas. All to no avail.
document.getElementById("file_display_area").appendChild(img);
document.getElementById("img_file_display_area").src = img.src;
console.log(img.width + '|' + img.height + '||' + new_size[0] + '|' + new_size[1]);
}

Get original dimensions of resized html image element

Is there a simple and efficient way to get the true dimensions (in JavaScript) of an image that is displayed in an <img> element with a potentially different rendered size (e.g. via max-height or max-width)?

There is present naturalWidth and naturalHeight DOM attributes.
For example:
var image = new Image();
image.src = "test.jpg";
image.onload = function() {
alert('width - ' + image.naturalWidth);
alert('height - ' + image.naturalHeight);
}
Or see example on jsFiddle.
More info at MDN

Sizing/stretching images to dimensions known only after page load

On my website, users can upload large images. I display these images like this:
<img id="userImage" src="userImage.ashx?width=740&id=4fc265d4-a83c-4069-8d6d-0fc78ae2840d">
userImage.ashx is a handler that returns image files based on id, so in this example the image for user 4fc265d4-a83c-4069-8d6d-0fc78ae2840d is returned. You can also set other attributes - in this example only width is given. The image is resized so that it is 740px wide.
I set the src of the image in javascript, once the rest of the page has loaded. By doing this I know how wide the image has to be to fill all the available space:
var width = document.getElementById("userImageHolder").getComputedSize().width;
document.getElementById("userImage").src = "flash/userImage.ashx?type=micrositePhoto&id=" + userId + "&width=" + width;
This all works, but the image doesn't load until everything else on the page has loaded. I have a complex solution to a simple problem.
Is there a better way to do this? What is the best way to shrink/stretch images to fill an area that is only known once the page loads?

Figure out what the upper limit is for width and height and generate the image to that size, then use max-width/max-height to allow the browser to auto scale it based on the size of the browser window.

Try to preload your images in a onDOMReady handler, and then insert in an onLoad one. While this can't guarantee the images to be loaded before everything else, they can at least start loading earlier.
Someting like this (using jQuery):
$(document).ready(function(){
var imageArray = [],
imageSrc = [];
//Fill image src array from somewhere
var len = imageSrc.length;
for(var i = 0; i < len; i++){
var img = new Image();
img.src = imageSrc[i];
img.onload = function(){
//Do something with your loaded image
imageArray.push(this);
}
}
});

Checking for existence of thumbnails and images

I am attempting to write some javascript in a page that needs to load one of three images. First it needs to check to see if a Thumbnail for a picture exists and display that, if the thumbnail does not exist, check for the full_size image and display that (scaled down) and if neither a thumbnail or a full-size image exists, use a noimage.gif as a small placeholder. What would be the most efficient way to do this?
Some stipulations, can't do it server side as there is no server. This java script is going to be inserted into a kml file as a . I am mapping a fiber network and this is for the hand-hole portion. Basically, each placemark will have any where from 1 to 5 pics and the names of the pics will be the same as the placemark name with a -1, -2, -3, etc. after each picture. So each of these placemarks gets its style from the same balloonstyle.... and the html I have written in this balloon style calls img src="./images/$[name]-1.jpg" width="120px" height="100px" where $[name] inserts the name of the placemark. This will allow for the users, when they update the kml file and add new placemarks, all they will have to do is rename the jpeg to match the placemark's name and add a -1 to the end of it and dump it in the images folder.... making it so the user doesn't have to edit ANY html (which is too much for them to do)

I would do the checking on the server, then have the server provide a resource path to the available image.

I agree with #Jason Dean,
But If you want to detect it by using JavaScript I would do like so:
When getting the thumbnail I would attach some kind of id/class property to it and check if it's present.
Check if id of "img-tumb" exists:
var imgThumb = document.getElementById("img-thumb");
if (imgThumb != null){
alert("Thumbnail exists");
}else{
//Check Image size...
Now to check the image size:(Placed after else of last if)
var img = document.getElementById('your_image_id');
var height = img.clientHeight;
var width = img.clientWidth;
To change the height after the image height was detected:
img.style.height = height-50;//Substracks 50 pixles from the original size
img.style.width = width-50;//Substracks 50 pixles from the original size
For you finale event(when none are detected), I would use the same checking as in phase one.
Complete code:
var imgThumb = document.getElementById("img-thumb");
var imgFull = document.getElementById("img-full");//Full sized image
if (imgThumb != null){
alert("Thumbnail exists");
}else if(imgFull != null){
//Check Image size...
alert("Full sized image exists");
var img = document.getElementById('your_image_id');
var height = img.clientHeight;
var width = img.clientWidth;
img.style.height = height-50;//Substracks 50 pixles from the original size
img.style.width = width-50;//Substracks 50 pixles from the original size
}else{
//Place noimage.gif
}

Getting an image's 'real' width and height in IE

I'm currently building a site and using the Shadowbox JS plugin to display images.
Because we serve up images via a JSP (rather than linking directly to image files), Shadowbox seems unable to dynamically determine their width and height and so just opens the images in an overlay of ~the screen size.
It's possible to manually pass in widths and heights to the shadowbox plugin using 'rel', so I've got around the problem for FF/Chrome/Safari using the following code:
$('#pic1img').attr("src")).load(function() {
picWidth = this.width;
picHeight = this.height;
});
$(window).load(
function() {
var w = $("#pic1img").width();
var h = $("#pic1img").height();
if( picWidth < w ){ picWidth = w; }
if( picHeight < h ){ picHeight = h; }
$('#pic1').attr('rel', 'shadowbox[pics];height=' + picHeight + ';width=' + picWidth);
}
);
But I can't find any way to do the same in IE.

The code actually worked once I began loading the thumbnails at full size and then setting their width and height after load.
The issue was that I was setting a surrounding div to
display: none
until the images were loaded and IE can't work out the sizes of hidden images.
Resolved this by setting
visibility: hidden
instead.