从画布图像中获取像素值，CORS限制 [英] get pixel value from canvas image, CORS restriction
问题描述
所以显然这是一个问题，一些浏览器，因为我尝试了一些关于画布被污染mumbo jumbo的命中，当你尝试从画布图像获取像素数据，如：
var pix = context.getImageData（3200,3200,1,1）.data;
到目前为止，我已经尝试过crossorigin = '和XMLHttpRequest，但我仍然得到相同的问题。然后再次，我不知道我是否实施它错了，只是一个noob。我将非常感谢，如果有人可以请帮助我这个问题。奋斗与它1.5天，之前转向论坛问题作为最后的手段。请注意，我的代码适用于Firefox浏览器，但不是Chrome ...它的关键是我的实现具有跨浏览器功能。这是一个小的JavaScript代码，我从我的主要项目中提取，以隔离，并尝试和解决问题：
html>
< head>
< / head>
< body>
< canvas id =myCanvaswidth =6029height =6968>< / canvas>
< script> <！ - Javascript section - >
var canvas = document.getElementById（'myCanvas'）; //通过标识从html代码获取画布
var context = canvas.getContext（'2d'）; //获取画布上下文
var imageObj = new Image（）; // create image object
imageObj.src ='gauteng.png'; //定义图像对象的图像
imageObj.onload = function（）//图像在图像对象中加载后触发函数
{
try
{
context.drawImage（imageObj，0,0）; //将图像对象绘制到画布的上下文上
var imgd = context.getImageData（3200,3200,1,1）; //在x coord 3200处获取像素，y coord 3200
var pix = imgd.data; //从像素获取RGB值
//使用alert
打印出RGB值alert（'R val ='+ pix [0] .toString（）+\r\\ \\ nG val =+ pix [1] .toString（）+\r\\\
B val =+ pix [2] .toString（））;
}
catch（err）//如果抛出异常，显示错误消息
{
alert（err.toString（））;
}
};
< / script>
< / body>
< / html>
我还可以包括我的XMLHttpRequest方法：
imageObj.onload = function（）{
try
{
var inputFile = new XMLHttpRequest
inputFile.open（'get'，'gauteng.png'，true）; //打开示例文件
inputFile.onreadystatechange = function（）
{
if（inputFile.readyState == 4）//文档准备解析
{
context.drawImage（imageObj，0，0）;
//像素位置from image
var imgd = context.getImageData（3200,3200,6029,6968）;
var pix = imgd.data;
alert（pix [0] .toString（）++ pix [1] .toString（）++ pix [2] .toString（））;
}
}
inputFile.send（null）; //完成后关闭文件
}
catch（err）{alert（err.toString（））;}
};先感谢您。 解决方案当它是跨源的，你正在使用画布很多问题都通过这样解决：
imageObj.crossOrigin ='anonymous';
//在设置src之前必须设置crossOrigin属性。
希望它有帮助
so obviously this is quite a problem with some browsers, because I googled a number of hits regarding the "canvas gets tainted" mumbo jumbo when you try and get pixel data from canvas images, like :
var pix = context.getImageData(3200,3200,1,1).data;
So far I already tried the crossorigin = '' and XMLHttpRequest, but I still get the same problem. Then again, I don't know if I'm implementing it wrong and just being a noob. I will greatly appreciate it if someone could please help me with this problem. Struggling with it 1.5 days, before turning to a forum question as last resort. Note that my code works for Firefox browsers, but not for Chrome... It his crucial that my implementation has cross-browser functionality. This is a small javascript code snipped I extracted from my main project to isolate, and try and fix, the problem:
<html>
<head>
</head>
<body>
<canvas id="myCanvas" width="6029" height="6968"></canvas>
<script> <!-- Javascript section-->
var canvas = document.getElementById('myCanvas'); //get canvas from html code via identity
var context = canvas.getContext('2d'); //get context of canvas
var imageObj = new Image(); //create image object
imageObj.src = 'gauteng.png'; //define the image of the image object
imageObj.onload = function() //trigger function after the image has loaded in image object
{
try
{
context.drawImage(imageObj,0,0); //draw the image object onto context of canvas
var imgd = context.getImageData(3200,3200,1,1); //get pixel at x coord 3200, and y coord 3200
var pix = imgd.data; //get the RGB values from pixel
// print out RGB values with alert
alert('R val= '+pix[0].toString()+ "\r\nG val= "+pix[1].toString()+"\r\nB val= "+pix[2].toString());
}
catch(err) //display error message if exception is thrown
{
alert(err.toString());
}
};
</script>
</body>
</html>
I can also include my approach for the XMLHttpRequest:
imageObj.onload = function() {
try
{
var inputFile = new XMLHttpRequest();
inputFile.open('get', 'gauteng.png', true); //open example file
inputFile.onreadystatechange = function()
{
if(inputFile.readyState==4) //document is ready to parse
{
context.drawImage(imageObj, 0, 0);
//pixel location from image
var imgd = context.getImageData(3200,3200,6029,6968);
var pix = imgd.data;
alert(pix[0].toString()+ " "+pix[1].toString()+" "+pix[2].toString());
}
}
inputFile.send(null); //close file after finished
}
catch(err){ alert(err.toString());}
};
Thank you in advance.
解决方案 when it is cross origin and you are working with canvas many issues are resolved by this:
imageObj.crossOrigin = 'anonymous';
// crossOrigin attribute has to be set before setting src.
Hope it helps
这篇关于从画布图像中获取像素值，CORS限制的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
