如何在画布上重新着色灰度图像

问题描述

在画布上绘制灰度图标(具有透明背景的 png 图像)时，是否有任何快速着色的方法?通过着色我的意思是把灰度图标变成绿色(给定颜色而不是灰色的阴影来匹配给定的颜色主题)

Is there any quick way to colorize greyscale icon (png image with transparent background) when drawing it on canvas? By colorize I mean turning greyscale icon into lets say greenscale (shades of given color instead of grey to match given color theme)

我知道我可以手动操作每个像素，但也许有一些更自动化的方法?

I know I could manipulate each pixel manually but maybe there's some more automated way?

推荐答案

使用合成将灰度图像重新着色为greenscale".

使用合成比像素操作更快，并且作为奖励，您不会违反跨域安全限制(如果您使用 getImageData 则可以这样做).

Using compositing is faster than pixel manipulation and as a bonus you won't run afoul of cross-domain security restrictions (which you do if you instead used getImageData).

1. 为您的图片创建一个完全绿色的版本.
2. 在画布上绘制灰度图像.
3. 设置 globalCompositeOperation='color'，这会使现有灰度像素重新着色(重新着色")，并在顶部绘制像素.
4. 在画布上绘制您的全绿色图像.

1. Create a fully green version of your image.
2. Draw your grayscale image on the canvas.
3. Set globalCompositeOperation='color' which causes existing grayscale pixels to be re-tinted ("re-hued") with pixels drawn on top.
4. Draw your fully green image on the canvas.

颜色"合成会将灰度变为绿色.

+ =

注意:需要具有混合功能的现代浏览器(Edge 而不是 IE)

示例代码和演示:

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;

var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/multple/koolBW.png";
function start(){

    // create a fully green version of img
    var c=document.createElement('canvas');
    var cctx=c.getContext('2d');
    c.width=img.width;
    c.height=img.height;
    cctx.drawImage(img,0,0);
    cctx.globalCompositeOperation='source-atop';
    cctx.fillStyle='green';
    cctx.fillRect(0,0,img.width,img.height);  
    cctx.globalCompositeOperation='source-over';

    // draw the grayscale image onto the canvas
    ctx.drawImage(img,0,0);

    // set compositing to color (changes hue with new overwriting colors) 
    ctx.globalCompositeOperation='color';

    // draw the fully green img on top of the grayscale image
    // ---- the img is now greenscale ----
    ctx.drawImage(c,0,0);
    
    // Always clean up -- change compositing back to default
    ctx.globalCompositeOperation='source-over';
}

body{ background-color:white; }
#canvas{border:1px solid red; }

<canvas id="canvas" width=256 height=256></canvas>

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