你好，我需要创建混合颜色工具，我尝试从画布中获取颜色像素getImageData并与我选择的颜色混合并获得平均颜色，我可以轻松获得它：
/* r1 = red channel from getImageData
g1 = green channel from getImageData
b1 = blue channel from getImageData
r2 = red channel my selected color
g2,b2 same
*/
var avR = Math.round(0.5*r1 + 0.5*r2);
var avG = Math.round(0.5*g1 + 0.5*g2);
var avB = Math.round(0.5*b1 + 0.5*b2);
当我绘图时，我尝试混合这种颜色，但混合效果不可用。
也许有人可以帮助我？http://jsfiddle.net/b72ky2sc/6/
i need that tool can get image in left side:
您没有说明足够的细节，但以下是如何在画布上使用混合模式。请注意，IE 还不支持其中任何一个（除了normal）所以在最近的 Firefox 或 Chrome 中测试一下。
当前修订版画布标准中的所有混合模式都列在下拉列表中，您可以使用它来选择模式。这样您就可以看到哪种模式最适合您的需要（尝试诸如hard-light以较低的 alpha 值作为开始...）。
（是的，我很无聊..:)）
var cont = document.getElementById("spots"), // UI elements
canvas = document.getElementById("canvas"),
alpha = document.getElementById("alpha"),
modes = document.getElementById("modes"),
ctx = canvas.getContext("2d"),
isDown = false, // defaults
color = "rgb(107, 122, 174)";
// set up color palette using a custom "Spot" object
// This will use a callback function when it is clicked, to
// change current color
function Spot(color, cont, callback) {
var div = document.createElement("div");
div.style.cssText = "width:50px;height:50px;border:1px solid #000;margin:0 1px 1px 0;background:" + color;
div.onclick = function() {callback(color)};
cont.appendChild(div);
}
// add some spot colors to our palette container
new Spot(color, cont, setColor);
new Spot("rgb(107, 174, 170)", cont, setColor);
new Spot("#00f", cont, setColor);
new Spot("#ff0", cont, setColor);
new Spot("#0ff", cont, setColor);
new Spot("#f0f", cont, setColor);
// this will set current fill style based on spot clicked
function setColor(c) {ctx.fillStyle = c}
// setup defaults
ctx.fillStyle = color;
ctx.globalAlpha = 0.5;
// events
canvas.onmousedown = function() {isDown = true};
window.onmouseup = function() {isDown = false};
window.onmousemove = function(e) {
if (!isDown) return;
var r = canvas.getBoundingClientRect(),
x = e.clientX - r.left,
y = e.clientY - r.top;
ctx.beginPath();
ctx.arc(x, y, 25, 0, 2*Math.PI);
ctx.fill();
};
alpha.onchange = function(){ctx.globalAlpha = alpha.value * 0.01};
modes.onchange = function(){ctx.globalCompositeOperation = modes.value};body{font:14px sans-serif;background:#333;color:#eee}
#spots {float:right}
#canvas {background:#fff;cursor:crosshair;border:1px solid #777}<label for="modes">Blending Modes:</label>
<select id="modes">
<option value="normal">normal</option>
<option value="multiply">multiply</option>
<option value="screen">screen</option>
<option value="overlay">overlay</option>
<option value="darken">darken</option>
<option value="lighten">lighten</option>
<option value="color-dodge">color-dodge</option>
<option value="color-burn">color-burn</option>
<option value="hard-light">hard-light</option>
<option value="soft-light">soft-light</option>
<option value="difference">difference</option>
<option value="exclusion">exclusion</option>
<option value="hue">hue</option>
<option value="saturation">saturation</option>
<option value="color">color</option>
<option value="luminosity">luminosity</option>
</select>
<label for="alpha">Alpha:</label><input id="alpha" type="range" min=0 max=100 value="50">
<br>
<canvas id="canvas" width=500 height=500></canvas><div id="spots"></div>