[js高手之路] html5 canvas系列教程 - 像素操作(反色,黑白,亮度,復古,蒙版,透明)

接著上文[js高手之路] html5 canvas系列教程 - 狀態詳解(save與restore)，相信大家都應該玩過美顏功能，而我們今天要講的就是canvas強大的像素處理能力，通過像素處理，實現反色，黑白，亮度，復古，蒙版，透明等美顏效果. getImageData：獲取一張圖片的像素數據 c ...

接著上文[js高手之路] html5 canvas系列教程 - 狀態詳解(save與restore)，相信大家都應該玩過美顏功能，而我們今天要講的就是canvas強大的像素處理能力，通過像素處理，實現反色，黑白，亮度，復古，蒙版，透明等美顏效果.

getImageData：獲取一張圖片的像素數據

cxt.getImageData( x, y, width, height )

x：圖片所在的x坐標

y: 圖片所在的y坐標

width,height 要獲取的像素區域

返回值是一個對象，對象包括一個data屬性，寬度，高度. data屬性是一個巨大的數組，數組中存儲的是這張圖片的所有像素信息，每四個一組組成一個像素點的信息，如：

[r1,g1,b1,a1, r2,g2,b2,a2...]， r( 紅色) g( 綠色) b( 藍色 ) a( 透明度 )

putImageData：輸出像素圖片

putImageData( 像素對象, x, y )

註意：getImageData會產生跨域問題，所以你的程式要放在web伺服器下，我這裡是放在phpstudy下麵.

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var oImg = new Image();
16             oImg.src = './img/mv.jpg';
17             oImg.onload = function () {
18                 oGc.drawImage(oImg, 10, 10);
19                 var imgData = oGc.getImageData(10, 10, 200, 200);
20                 console.log( imgData );
21             }
22         }
23     </script>
24 </head>
25 <body>
26     <canvas id="canvas" width="500" height="400"></canvas>
27 </body>
28 </html>

我這張圖片的尺寸是200 x 200.

一：反色效果

演算法：把每一個像素的r, g, b顏色取反就行，也就是( 255 - 原來的值 )

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var oImg = new Image();
16             oImg.src = './img/mv.jpg';
17             oImg.onload = function () {
18                 oGc.drawImage(oImg, 10, 10);
19                 var imgData = oGc.getImageData(10, 10, 200, 200),
20                     data = imgData.data;
21                 for( var i = 0; i < data.length; i += 4 ) {
22                     data[i] = 255 - data[i];
23                     data[i+1] = 255 - data[i+1];
24                     data[i+2] = 255 - data[i+2];
25                 }
26                 //處理完之後，再次輸出
27                 oGc.putImageData( imgData, 220, 10 );
28             }
29         }
30     </script>
31 </head>
32 <body>
33     <canvas id="canvas" width="500" height="400"></canvas>
34 </body>
35 </html>

二、黑白效果（灰度圖）

將彩色圖片轉換成黑白圖片，原理：求r(data[i]), g(data[i+1]), b(data[i+2])三個通道的平均值，然後把這個平均值賦值給r, g, b

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var oImg = new Image();
16             oImg.src = './img/mv.jpg';
17             oImg.onload = function () {
18                 oGc.drawImage(oImg, 10, 10);
19                 var imgData = oGc.getImageData(10, 10, 200, 200),
20                     data = imgData.data, avg = 0;
21                 for( var i = 0; i < data.length; i += 4 ) {
22                     avg = ( data[i] + data[i+1] + data[i+2] ) / 3;
23                     data[i] = avg;
24                     data[i+1] = avg;
25                     data[i+2] = avg;
26                 }
27                 //處理完之後，再次輸出
28                 oGc.putImageData( imgData, 220, 10 );
29             }
30         }
31     </script>
32 </head>
33 <body>
34     <canvas id="canvas" width="500" height="400"></canvas>
35 </body>
36 </html>

也可以分配rgb的灰度比例

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var oImg = new Image();
16             oImg.src = './img/mv.jpg';
17             oImg.onload = function () {
18                 oGc.drawImage(oImg, 10, 10);
19                 var imgData = oGc.getImageData(10, 10, 200, 200),
20                     data = imgData.data, avg = 0;
21                 for( var i = 0; i < data.length; i += 4 ) {
22                     avg = data[i] * 0.3 + data[i+1] * 0.3 + data[i+2] * 0.4;
23                     data[i] = avg;
24                     data[i+1] = avg;
25                     data[i+2] = avg;
26                 }
27                 //處理完之後，再次輸出
28                 oGc.putImageData( imgData, 220, 10 );
29             }
30         }
31     </script>
32 </head>
33 <body>
34     <canvas id="canvas" width="500" height="400"></canvas>
35 </body>
36 </html>

三、調節亮度的強弱

在r、g、b、通道上加上一正值就是變亮，加上負值就是變暗

 1 var oImg = new Image();
 2 oImg.src = './img/mv.jpg';
 3 oImg.onload = function () {
 4     oGc.drawImage(oImg, 10, 10);
 5     var imgData = oGc.getImageData(10, 10, 200, 200),
 6         data = imgData.data, avg = 0;
 7     for( var i = 0; i < data.length; i += 4 ) {
 8         data[i] += 30;
 9         data[i+1] += 50;
10         data[i+2] += 50;
11     }
12     //處理完之後，再次輸出
13     oGc.putImageData( imgData, 220, 10 );
14 }

變暗：

data[i] -= 30; data[i+1] -= 50; data[i+2] -= 50;

四、復古效果

將r, g, b按比例混合相加。

 1 var oImg = new Image();
 2 oImg.src = './img/mv.jpg';
 3 oImg.onload = function () {
 4     oGc.drawImage(oImg, 10, 10);
 5     var imgData = oGc.getImageData(10, 10, 200, 200),
 6         data = imgData.data, avg = 0;
 7     for( var i = 0; i < data.length; i += 4 ) {
 8         r = data[i];
 9         g = data[i+1];
10         b = data[i+2];
11         data[i] = r * 0.3 + g * 0.4 + b * 0.3;
12         data[i+1] = r * 0.2 + g * 0.6 + b * 0.2;
13         data[i+2] = r * 0.4 + g * 0.3 + b * 0.3;
14     }
15     //處理完之後，再次輸出
16     oGc.putImageData( imgData, 220, 10 );
17 }

五、藍色蒙版

藍色蒙版就是讓圖片偏藍色，將藍色通道賦值為 r, g, b三原色的平均值，把綠色，紅色通道設置為0，其他蒙版效果，只要設置對應的通道平均值，關閉其他通道即可.

 1 var oImg = new Image();
 2 oImg.src = './img/mv.jpg';
 3 oImg.onload = function () {
 4     oGc.drawImage(oImg, 10, 10);
 5     var imgData = oGc.getImageData(10, 10, 200, 200),
 6         data = imgData.data, avg = 0;
 7     for( var i = 0; i < data.length; i += 4 ) {
 8         avg = ( data[i] + data[i+1] + data[i+2] / 3 );
 9         data[i] = 0;
10         data[i+1] = 0;
11         data[i+2] = avg;
12     }
13     //處理完之後，再次輸出
14     oGc.putImageData( imgData, 220, 10 );
15 }

六、透明度

這個很簡單，只要把透明度乘以一個0~1之間的值即可。跟css的opacity一樣

 1 var oImg = new Image();
 2 oImg.src = './img/mv.jpg';
 3 oImg.onload = function () {
 4     oGc.drawImage(oImg, 10, 10);
 5     var imgData = oGc.getImageData(10, 10, 200, 200),
 6         data = imgData.data, avg = 0;
 7     for( var i = 0; i < data.length; i += 4 ) {
 8         data[i+3] *= 0.2;
 9     }
10     //處理完之後，再次輸出
11     oGc.putImageData( imgData, 220, 10 );
12 }

七、createImageData：根據圖片或者某個寬度與高度創建一個像素區域

cxt.createImageData( w, h )

cxt.createImageData( imgData )

w, h:創建區域的寬度與高度

imgData: 創建的區域與這個像素區域的寬度和高度相同，imgData就是通過getImageData獲取到圖片像素的返回值

1，根據一個圖片的寬度與高度，創建一個透明的紅色像素區域

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var oImg = new Image();
16             oImg.src = './img/mv.jpg';
17             oImg.onload = function () {
18                 oGc.drawImage(oImg, 10, 10);
19                 var imgData = oGc.getImageData(10, 10, 200, 200),
20                     data = imgData.data,
21                     imgData2 = oGc.createImageData( imgData ),
22                     data2 = imgData2.data;
23                 for( var i = 0; i < imgData2.width * imgData2.height * 4; i += 4 ) {
24                     data2[i] = 255;
25                     data2[i+1] = 0;
26                     data2[i+2] = 0;
27                     data2[i+3] = 30;
28                 }
29                 //處理完之後，再次輸出
30                 oGc.putImageData( imgData2, 220, 10 );
31             }
32         }
33     </script>
34 </head>
35 <body>
36     <canvas id="canvas" width="500" height="400"></canvas>
37 </body>
38 </html>

2，自定一個200 x 200的藍色透明像素區域

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset='utf-8' />
 5     <style>
 6         #canvas {
 7             border: 1px dashed #aaa;
 8         }
 9     </style>
10     <script>
11         window.onload = function () {
12             var oCanvas = document.querySelector("#canvas"),
13                 oGc = oCanvas.getContext('2d');
14 
15             var imgData = oGc.createImageData( 200, 200 ),
16                 data = imgData.data;
17                 for( var i = 0; i < imgData.width * imgData.height * 4 ; i += 4 ){
18                     data[i] = 0;
19                     data[i+1] = 0;
20                     data[i+2] = 255;
21                     data[i+3] = 100;
22                 }
23             oGc.putImageData( imgData, 10, 10 );
24         }
25     </script>
26 </head>
27 <body>
28     <canvas id="canvas" width="500" height="400"></canvas>
29 </body>
30 </html>