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[英]Javascript - getImageData after fillRect and drawImage
[英]JavaScript canvas drawImage getImageData
我無法理解兩種方法如何與畫布一起工作: drawImage getImageData 實際上,我想將位圖圖像解析為一個 RGBA 點數組,能夠轉換它並使用 putImageData 方法顯示它。 但只有一件事有效:drawImage 或 getImageData。 我尋求幫助 - 解釋這些方法如何相互影響。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title> Canvas to array </title>
</head>
<body>
<canvas id="canvas" width="1200" height="600" />
<script>
"use strict"
let imageData;
let My_img = new Image();
My_img.src = 'test1.jpg';
let cnv = document.getElementById("canvas");
let ctx = cnv.getContext("2d");
My_img.onload = function() {
ctx.drawImage(My_img, 0, 0);
imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
for (let i=0; i<imageData.data.length; i+=4){
imageData.data[i]=0;
imageData.data[i+1]=255;
imageData.data[i+2]=0;
imageData.data[i+3]=222;
}
ctx.putImageData(imageData,300,300);
};
</script>
</body>
</html>
您需要將圖像對象上的跨域標志設置為“匿名”。
My_img.crossOrigin = "Anonymous";
另請參閱: 如何修復 getImageData() 錯誤畫布已被跨域數據污染?
let ctx = document.getElementById("canvas").getContext("2d"); let img = new Image(); img.crossOrigin = "Anonymous"; img.src = 'https://placekitten.com/200/138'; img.onload = function() { ctx.drawImage(img, 0, 0); setTimeout(() => filterImage(ctx), 1000); }; // Multiply the value of the red channel by 2 and the blue channel by 3. function filterImage(ctx) { let d = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height); for (let i = 0; i < d.data.length; i += 4) { d.data[i + 0] = Math.min(Math.floor(d.data[i + 0] * 2.0), 0xFF); // R d.data[i + 1] = Math.min(Math.floor(d.data[i + 1] * 1.0), 0xFF); // G d.data[i + 2] = Math.min(Math.floor(d.data[i + 2] * 3.0), 0xFF); // B d.data[i + 3] = 0xFF; // A } ctx.putImageData(d, 0, 0); }
<canvas id="canvas" width="200" height="138" />
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