我有一个png图像,我想转换成灰度级.我设法将其转换为灰度,但它也会改变图像透明度的颜色.如何在不改变图像的透明区域的情况下更改其颜色？
- var canvas = document.getElementById('canvas');
- var ctx = canvas.getContext('2d');
- var img = new Image();
- img.src = 'image.png';
- ctx.drawImage(img,0);
- var imageData = ctx.getImageData(0,420,420);
- var px = imageData.data;
- var len = px.length;
- for (var i = 0; i < len; i+=4) {
- var redPx = px[i];
- var greenPx = px[i+1];
- var bluePx = px[i+2];
- var alphaPx = px[i+3];
- var greyScale = redPx * .3 + greenPx * .59 + bluePx * .11;
- px[i] = greyScale;
- px[i+1] = greyScale;
- px[i+2] = greyScale;
- px[i+3] = greyScale;
- }
- ctx.putImageData(imageData,0);
解决方法
阿尔法是“不是一种颜色”.您应该将其原样复制,使透明部分透明.只需删除行：
- px[i+3] = greyScale;
