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最佳答案

W3C 文档中有一节是关于像素操作的。

var context = document.getElementById('myCanvas').getContext('2d');


// Get the CanvasPixelArray from the given coordinates and dimensions.
var imgd = context.getImageData(x, y, width, height);
var pix = imgd.data;


// Loop over each pixel and invert the color.
for (var i = 0, n = pix.length; i < n; i += 4) {
pix[i  ] = 255 - pix[i  ]; // red
pix[i+1] = 255 - pix[i+1]; // green
pix[i+2] = 255 - pix[i+2]; // blue
// i+3 is alpha (the fourth element)
}


// Draw the ImageData at the given (x,y) coordinates.
context.putImageData(imgd, x, y);

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是的，看看 getImageData()。这里有一个用 JavaScript 破解 CAPTCHA 的例子:

JavaScript 中的 OCR 和神经网络

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试试 getImageData方法:

var data = context.getImageData(x, y, 1, 1).data;
var rgb = [ data[0], data[1], data[2] ];

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请注意，getImageData返回一个快照:

更改将在随后的 putImageData中生效
getImageData和 putImageData呼叫相对较慢

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是的，当然，只要你有它的上下文

var imgData = context.getImageData(0,0,canvas.width,canvas.height)
// { data: [r,g,b,a,r,g,b,a,r,g,..], ... }


function getPixel(imgData, index) {
var i = index*4, d = imgData.data
return [d[i],d[i+1],d[i+2],d[i+3]] // Returns array [R,G,B,A]
}


// AND/OR


function getPixelXY(imgData, x, y) {
return getPixel(imgData, y*imgData.width+x)
}

PS: If you plan to mutate the data and draw them back on the canvas, you can use subarray

var
idt = imgData, // See previous code snippet
a = getPixel(idt, 188411), // Array(4) [0, 251, 0, 255]
b = idt.data.subarray(188411*4, 188411*4 + 4) // Uint8ClampedArray(4) [0, 251, 0, 255]


a[0] = 255 // Does nothing
getPixel(idt, 188411) // Array(4) [0, 251, 0, 255]


b[0] = 255 // Mutates the original imgData.data
getPixel(idt, 188411) // Array(4) [255, 251, 0, 255]


// Or use it in the function
function getPixel(imgData, index) {
var i = index*4, d = imgData.data
return imgData.data.subarray(i, i+4) // Returns subarray [R,G,B,A]
}

你可以在 http://qry.me/xyscope/上试验一下，这个的代码在源代码中，只需要在控制台中复制/粘贴它。

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//Get pixel data
var imageData = context.getImageData(x, y, width, height);


//Color at (x,y) position
var color = [];
color['red'] = imageData.data[((y*(imageData.width*4)) + (x*4)) + 0];
color['green'] = imageData.data[((y*(imageData.width*4)) + (x*4)) + 1];
color['blue'] = imageData.data[((y*(imageData.width*4)) + (x*4)) + 2];
color['alpha'] = imageData.data[((y*(imageData.width*4)) + (x*4)) + 3];

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function GetPixel(context, x, y)
{
var p = context.getImageData(x, y, 1, 1).data;
var hex = "#" + ("000000" + rgbToHex(p[0], p[1], p[2])).slice(-6);
return hex;
}


function rgbToHex(r, g, b) {
if (r > 255 || g > 255 || b > 255)
throw "Invalid color component";
return ((r << 16) | (g << 8) | b).toString(16);
}

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你可以使用 i << 2。

const data = context.getImageData(x, y, width, height).data;
const pixels = [];


for (let i = 0, dx = 0; dx < data.length; i++, dx = i << 2) {
pixels.push({
r: data[dx  ],
g: data[dx+1],
b: data[dx+2],
a: data[dx+3]
});
}

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如果你想通过传递像素的坐标到函数中来提取像素的特定颜色，这将派上用场:

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
function detectColor(x, y){
data=ctx.getImageData(x, y, 1, 1).data;
col={
r:data[0],
g:data[1],
b:data[2]
};
return col;
}

x，y是要过滤掉颜色的坐标。

var color = detectColor(x, y)

颜色是对象，你会得到的 RGB 值由 color.r，color.g，color.b。

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又快又方便

使用下面的类实现 this article中描述的快速方法，包含所有你需要的: readPixel，putPixel，获取 width/height。调用 refresh()方法后的类更新画布。实例求解二维波动方程波动方程的简单情况

class Screen{
constructor(canvasSelector) {
this.canvas = document.querySelector(canvasSelector);
this.width  = this.canvas.width;
this.height = this.canvas.height;
this.ctx = this.canvas.getContext('2d');
this.imageData = this.ctx.getImageData(0, 0, this.width, this.height);
this.buf = new ArrayBuffer(this.imageData.data.length);
this.buf8 = new Uint8ClampedArray(this.buf);
this.data = new Uint32Array(this.buf);
}
  

// r,g,b,a - red, gren, blue, alpha components in range 0-255
putPixel(x,y,r,g,b,a=255) {
this.data[y * this.width + x] = (a << 24) | (b << 16) | (g <<  8) | r;
}
  

readPixel(x,y) {
let p= this.data[y * this.width + x]
return [p&0xff, p>>8&0xff, p>>16&0xff, p>>>24];
}


refresh() {
this.imageData.data.set(this.buf8);
this.ctx.putImageData(this.imageData, 0, 0);
}
}








// --------
// TEST
// --------


let s=new Screen('#canvas');


function draw() {


for (var y = 1; y < s.height-1; ++y) {
for (var x = 1; x < s.width-1; ++x) {
let a = [[1,0],[-1,0],[0,1],[0,-1]].reduce((a,[xp,yp])=>
a+= s.readPixel(x+xp,y+yp)[0]
,0);
let v=a/2-tmp[x][y];
tmp[x][y]=v<0 ? 0:v;
}
}


for (var y = 1; y < s.height-1; ++y) {
for (var x = 1; x < s.width-1; ++x) {
let v=tmp[x][y];
tmp[x][y]= s.readPixel(x,y)[0];
s.putPixel(x,y, v,v,v);
}
}


s.refresh();
window.requestAnimationFrame(draw)
}


// temporary 2d buffer ()for solving wave equation)
let tmp = [...Array(s.width)].map(x => Array(s.height).fill(0));


function move(e) { s.putPixel(e.x-10, e.y-10, 255,255,255);}


draw();

<canvas id="canvas" height="150" width="512" onmousemove="move(event)"></canvas>
<div>Move mouse on black box</div>

Get a pixel from HTML Canvas?

又快又方便