从输入[type = file]缩放图像 [英] Scaling image from input[type=file]
问题描述
所需结果:我希望从文件上传表单中选择一个图像,将其缩放到缩略图并显示它。
Desired Result: I'm looking to select an image from a file upload form, scale it to a thumbnail and display it.
问题:以下代码执行正是我想要它,但是,我必须选择文件不是一次,而是两次看图像预览。 (选择图像,没有显示,选择相同的图像,我得到缩放的显示)当我手动分配宽度和放大时,一切都很好用。高度,虽然现在我正在缩放它 - 这个问题开始了。我需要进行代码审查!当我注释掉if / if else / else语句并手动分配img.width& img.height是每个75,我得到显示虽然它当然没有缩放。
Problem: The following code does exactly what I want it to, however, I must select the file not once, but twice to see the image preview. (Select image, no display, select same image, I get the scaled display) Everything was working great when I was manually assigning width & height, though now that i'm scaling it - this issue began. I'm in need of a code review! When I comment out the if/if else / else statement and manually assign img.width & img.height to be 75 each, I get the display though it's of course not scaled.
previewFiles = function (file, i) {
preview = function (file) {
// Make sure `file.name` matches our extensions criteria
switch (/\.(jpe?g|png|gif)$/i.test(file.name)) {
case true:
var reader = new FileReader();
reader.onload = function (e) {
var img = new Image();
img.src = reader.result;
var width = img.width,
height = img.height,
max_size = 75;
if (width <= max_size && height <= max_size) {
var ratio = 1;
} else if (width > height) {
var ratio = max_size / width;
} else {
var ratio = max_size / height;
}
img.width = Math.round(width * ratio);
img.height = Math.round(height * ratio);
img.title = file.type;
$('div.box.box-primary').find('span.prev').eq(i).append(img);
};
reader.readAsDataURL(file);
break;
default:
$('div.box.box-primary').find('span.prev').eq(i).append('<a class="btn btn-app" href="#"><span class="vl vl-bell-o"></span> Unsupported File</a>');
break;
}
};
preview(file);
};
我已经稍微改变了一点 - 试过 https://hacks.mozilla.org/2011/01/how-to-develop-a -html5-image-uploader / 在本文之后,我遇到了同样的问题。这个问题是因为我没有使用画布吗?我很新w / jQuery& javascript - 非常感谢任何帮助!
I have changing the scaling up a bit - tried https://hacks.mozilla.org/2011/01/how-to-develop-a-html5-image-uploader/ following this article and I have the same issue. Is the problem due to the fact that i'm not using a canvas? I'm pretty new w/jQuery & javascript - Any help here is greatly appreciated!
推荐答案
我制作了一个获取图像的片段,缩略图&将其作为img元素导出。
I made this snippet that fetches an image, thumbnails it & exports it as an img element.
// limit the image to 150x100 maximum size
var maxW=150;
var maxH=100;
var input = document.getElementById('input');
input.addEventListener('change', handleFiles);
function handleFiles(e) {
var img = new Image;
img.onload = function() {
var canvas=document.createElement("canvas");
var ctx=canvas.getContext("2d");
var iw=img.width;
var ih=img.height;
var scale=Math.min((maxW/iw),(maxH/ih));
var iwScaled=iw*scale;
var ihScaled=ih*scale;
canvas.width=iwScaled;
canvas.height=ihScaled;
ctx.drawImage(img,0,0,iwScaled,ihScaled);
var thumb=new Image();
thumb.src=canvas.toDataURL();
document.body.appendChild(thumb);
}
img.src = URL.createObjectURL(e.target.files[0]);
}
body{ background-color: ivory; }
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Select a file to create a thumbnail from</h4>
<input type="file" id="input"/>
<br>
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