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javascript - 在上下文之间复制和操作图像数据

转载 作者:行者123 更新时间:2023-12-03 09:27:48 25 4
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我正在尝试:

  1. 将图像加载到 Canvas 上。
  2. 获取其imageData
  3. 操纵其 RGBA 值。
  4. 将修改后的图像数据写入另一个上下文。

我已经编写了以下代码( JSFiddle ),它可以满足我的需要,但是基于此 example 的它太静态了.

在调试代码时,似乎 imageData 正在被更改,但是当将其写入上下文时,会显示默认图像,而不是更改后的图像。

var globalFilters = {
greyscale : function(rgba) {
var avg = (rgba.a + rgba.g + rgba.b) / 3;
return {
r: function (v) { return avg; },
g: function (v) { return avg; },
b: function (v) { return avg; }
};
},
luma : function(rgba) {
var lum = rgba.a * 0.299 + rgba.g * 0.587 + rgba.b * 0.114;
return {
r: function (v) { return lum; },
g: function (v) { return lum; },
b: function (v) { return lum; }
};
},
invertColor : function(rgba) {
var avg = (rgba.a + rgba.g + rgba.b) / 3;
return {
r: function (v) { return 255 - v; },
g: function (v) { return 255 - v; },
b: function (v) { return 255 - v; }
};
},
channelRotate : function(rgba) {
return {
r: function (v) { return rgba.g; },
g: function (v) { return rgba.b; },
b: function (v) { return rgba.r; }
};
},
channelRotate2 : function(rgba) {
return {
r: function (v) { return rgba.b; },
g: function (v) { return rgba.r; },
b: function (v) { return rgba.g; }
};
}
};

function imageLoaded(e) {
var canvas = document.getElementById('draw');
var ctx = canvas.getContext('2d');
var img = e.target;
var imgW = img.width;
var imgH = img.height;

var rows = 2;
var cols = 2;
var filters = [ 'channelRotate', 'channelRotate2', 'invertColor' ];

// Set the width and height of the canvas
var width = imgW * cols;
var height = imgH * rows;

canvas.width = width;
canvas.height = height;

// Get all canvas pixel data
var imgData = getImageData(img);

ctx.putImageData(imgData, 0, 0);

for (var i = 1; i <= filters.length; i++) {
var filter = globalFilters[filters[i - 1]];
var pixelCache = {};
var row = Math.floor(i / rows);
var col = i % cols;
var yOffsetStart = row * imgH;
var yOffsetEnd = yOffsetStart + imgH;

for (var off = 0, y = yOffsetStart; y < yOffsetEnd; y++, off+=4) {
var xOffsetStart = col * imgW;
var xOffsetEnd = xOffsetStart + imgW;

for (var x = xOffsetStart; x < xOffsetEnd; x++) {
var rgba = getRGBA(off, imgData.data);
var pixel = rgbaToInt(rgba);

var rgbaOut;
if (pixelCache[pixel]) {
rgbaOut = pixelCache[pixel];
} else {
rgbaOut = transformRGBA(rgba, filter.call(null, rgba, pixel));
pixelCache[pixel] = rgbaOut;
}

setRGBA(off, imgData.data, rgbaOut);
}
}

ctx.putImageData(imgData, col * imgH, row * imgH);
}
}

function getImageData(img) {
var canvas = document.createElement('canvas');
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
return ctx.getImageData(0, 0, canvas.width, canvas.height);
}

function rgbaToInt(rgba) {
return (rgba.r << 24) + (rgba.g << 16) + (rgba.b << 8) + (rgba.a);
}

function getRGBA(offset, data) {
return {
r: data[offset + 0],
g: data[offset + 1],
b: data[offset + 2],
a: data[offset + 3]
};
}

function setRGBA(offset, data, rgb) {
data[offset + 0] = rgb.r || 0;
data[offset + 1] = rgb.g || 0;
data[offset + 2] = rgb.b || 0
data[offset + 3] = rgb.a || 0;
}

function transformRGBA(rgba, filterFn) {
return {
r: clamp(filterFn.r ? filterFn.r.call(null, rgba.r) : rgba.r, 255),
g: clamp(filterFn.g ? filterFn.g.call(null, rgba.g) : rgba.g, 255),
b: clamp(filterFn.b ? filterFn.b.call(null, rgba.b) : rgba.b, 255),
a: clamp(filterFn.a ? filterFn.a.call(null, rgba.a) : rgba.a, 255)
};
}

function clamp(value, min, max) {
if (arguments.length === 2) {
max = min;
min = 0;
}
if (value < min) return min;
if (value > max) return max;
return value;
}

var img = new Image();
img.crossOrigin = 'Anonymous';
img.onload = imageLoaded;
img.src = 'http://i.imgur.com/48KdD3D.jpg?1';
body {
background: #208;
}
canvas {
border: thin solid #333;
}
<canvas id="draw">Canvas</canvas>

最佳答案

第一个问题是您的过滤没有更改 imgData.data

[更新]

enter image description here

这里是导出过滤 Canvas 而不是导出 imageData 的重构代码。

var globalFilters = {
unchanged : function(rgba) {
return {
r: function (v) { return v; },
g: function (v) { return v; },
b: function (v) { return v; }
};
},
greyscale : function(rgba) {
var avg = (rgba.a + rgba.g + rgba.b) / 3;
return {
r: function (v) { return avg; },
g: function (v) { return avg; },
b: function (v) { return avg; }
};
},
luma : function(rgba) {
var lum = rgba.a * 0.299 + rgba.g * 0.587 + rgba.b * 0.114;
return {
r: function (v) { return lum; },
g: function (v) { return lum; },
b: function (v) { return lum; }
};
},
invertColor : function(rgba) {
var avg = (rgba.a + rgba.g + rgba.b) / 3;
return {
r: function (v) { return 255 - v; },
g: function (v) { return 255 - v; },
b: function (v) { return 255 - v; }
};
},
channelRotate : function(rgba) {
return {
r: function (v) { return rgba.g; },
g: function (v) { return rgba.b; },
b: function (v) { return rgba.r; }
};
},
channelRotate2 : function(rgba) {
return {
r: function (v) { return rgba.b; },
g: function (v) { return rgba.r; },
b: function (v) { return rgba.g; }
};
},
applyFilter:function(img,filterName){
var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
var filter = globalFilters[filterName];
var imgW=canvas.width=img.width;
var imgH=canvas.height=img.height;
ctx.drawImage(img,0,0);
//
var imgData=ctx.getImageData(0,0,imgW,imgH);
var data=imgData.data;
for(var i=0;i<data.length;i+=4){
var rgba=this.getRGBA(i,data);
var rgbaOut=this.transformRGBA(rgba, filter.call(null, rgba));
this.setRGBA(i,data,rgbaOut);
}
ctx.putImageData(imgData,0,0);
return(canvas);
},
getRGBA:function(offset, data) {
return {
r: data[offset + 0],
g: data[offset + 1],
b: data[offset + 2],
a: data[offset + 3]
};
},
setRGBA:function(offset, data, rgb) {
data[offset + 0] = rgb.r || 0;
data[offset + 1] = rgb.g || 0;
data[offset + 2] = rgb.b || 0
data[offset + 3] = rgb.a || 0;
},
transformRGBA:function(rgba, filterFn) {
return {
r: this.clamp(filterFn.r ? filterFn.r.call(null, rgba.r) : rgba.r, 255),
g: this.clamp(filterFn.g ? filterFn.g.call(null, rgba.g) : rgba.g, 255),
b: this.clamp(filterFn.b ? filterFn.b.call(null, rgba.b) : rgba.b, 255),
a: this.clamp(filterFn.a ? filterFn.a.call(null, rgba.a) : rgba.a, 255)
};
},
clamp:function(value, min, max) {
if (arguments.length === 2) {
max = min;
min = 0;
}
if (value < min) return min;
if (value > max) return max;
return value;
}
};

// list of filters to apply
var filters=['unchanged','channelRotate','channelRotate2','invertColor'];
// #cols on #draw canvas
var cols=2;
var rows=Math.ceil(filters.length/cols);

// load image (must satisfy CORS)
var img = new Image();
img.crossOrigin = 'Anonymous';
img.onload = imageLoaded;
img.src = 'http://i.imgur.com/48KdD3D.jpg?1';

// draw the filtered images onto #draw canvas
function imageLoaded(){
var img=this;
var draw=document.getElementById('draw');
var ctx=draw.getContext('2d');
draw.width=cols*img.width;
draw.height=rows*img.height;
for(var i=0;i<filters.length;i++){
var c=globalFilters.applyFilter(img,filters[i]);
var row=parseInt(i/cols);
var col=(i-row*cols);
ctx.drawImage(c,col*img.width,row*img.height);
}
}
body{ background-color: ivory; }
canvas{border:1px solid red;}
<canvas id="draw" width=300 height=300></canvas>

关于javascript - 在上下文之间复制和操作图像数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31609311/

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