使用canvas进行图像编辑的实例

W(宽) = canvas.width * scale
H(高) = canvas.height * scale
x坐标 = (W - canvas.width)/2;
y坐标 = (H - canvas.height)/2;

<canvas id="drawing" >
 <p>The canvas element is not supported!</p>
</canvas>
<br>
<input id="scale-range" min="0.5" max="1.5" step="0.01" type="range" >
<script>
var drawing = document.getElementById('drawing');
if(drawing.getContext){
 var context = drawing.getContext('2d');
 var slider = document.getElementById('scale-range');
 var W = 400;
 var H = 290; 
 drawing.width = W; 
 drawing.height = H;
 var image = new Image();
 image.src="http://sandbox.runjs.cn/uploads/rs/26/ddzmgynp/chunfen.jpg";
 image.onload = function(){
 drawImgByScale(slider.value);
 slider.onmousemove = function(){
 drawImgByScale(slider.value);
 }
 }
 function drawImgByScale(scale){
 var imgW = W * scale;
 var imgH = H * scale;
 var dx =(W - imgW)/2;
 var dy =(H - imgH)/2;
 context.clearRect(0,0,W,H);
 context.drawImage(image,dx,dy,imgW,imgH);
 }
} 
</script>

<canvas id="drawing" >
 <p>The canvas element is not supported!</p>
</canvas>
<div>
 <span>
 <input type="file" id="addImgHelper" >
 <button id="addImg">选择图片</button>
 </span>
 <span>
 <button id="addWaterMark" disabled>添加水印</button> 
 <span>水印文字为</span>
 <input id="waterMarkWords" type="text" value="小火柴的蓝色理想"> 
 </span>
 <span>
 <button id="downloadImg" disabled>下载图片</button>
 <a id="downloadImgHelper" href="#" rel="external nofollow" download="带水印图片" ></a> 
 </span>
</div>
<script>
if(drawing.getContext){
 var cxt = drawing.getContext('2d');
 var W,H; 
 addImg.onclick = function(){
 addImgHelper.click();
 }
 addImgHelper.onchange = function(){
 addWaterMark.disabled = true;
 downloadImg.disabled = true;
 var file = addImgHelper.files[0];
 if(file && /image/.test(file.type)){
 var reader = new FileReader();
 reader.readAsDataURL(file);
 reader.onload = function(){
 var img = new Image();
 img.src= reader.result;
 img.onload = function(){
 addWaterMark.disabled = false;
 drawing.width = W = img.width;
 drawing.height = H = img.height;
 cxt.drawImage(img,0,0);
 addWaterMark.onclick = function(){
 downloadImg.disabled = false;
 cxt.clearRect(0,0,W,H);
 cxt.drawImage(img,0,0); 
 var str = waterMarkWords.value;
 cxt.font = "bold 50px Arial";
 cxt.lineWidth = '1';
 cxt.fillStyle = 'rgba(255,255,255,0.5)';
 cxt.textBaseline = "bottom";
 cxt.textAlign = 'end';
 cxt.fillText(str,W-10,H-10,W/2); 
 downloadImg.onclick = function(){
 downloadImgHelper.href = drawing.toDataURL('image/png');
 downloadImgHelper.click(); 
 } 
 } 
 }
 } 
 } 
 } 
}
</script>

<canvas id="drawing" >
 <p>The canvas element is not supported!</p>
</canvas>
<canvas id="drawingOff" >
 <p>The canvas element is not supported!</p>
</canvas>
<script>
if(drawing.getContext){
 var cxt = drawing.getContext('2d');
 var cxtOff = drawingOff.getContext('2d');
 var W,H; 
 var scale = 1.5; 
 var img = new Image();
 img.src="http://sandbox.runjs.cn/uploads/rs/26/ddzmgynp/chunfen.jpg";
 img.onload = function(){
 W = img.width;
 H = img.height;
 drawing.width = W/scale;
 drawing.height = H/scale;
 drawingOff.width = W;
 drawingOff.height = H;
 cxt.drawImage(img,0,0,W/scale,H/scale);
 cxtOff.drawImage(img,0,0);
 drawing.onmousedown = function(e){
 e = e || event;
 var x0 = this.offsetLeft;
 var y0 = this.offsetTop; 
 drawMagnifier(e);
 drawing.onmousemove = function(e){
 drawMagnifier(e);
 }
 document.onmouseup = function(e){
 cxt.clearRect(0,0,W/scale,H/scale);
 cxt.drawImage(img,0,0,W/scale,H/scale);
 drawing.onmousemove = null;
 } 
 function drawMagnifier(e){
 cxt.clearRect(0,0,W/scale,H/scale);
 cxt.drawImage(img,0,0,W/scale,H/scale);
 var x = (e.clientX-x0);
 var y = (e.clientY-y0); 
 var r = 40;
 var dx = x - r;
 var dy = y - r;
 var sx = x*scale - r;
 var sy = y*scale - r;
 cxt.save();
 cxt.beginPath();
 cxt.arc(x,y,r,0,Math.PI*2);
 cxt.lineWidth = 4;
 cxt.strokeStyle = '#069';
 cxt.stroke();
 cxt.clip();
 cxt.drawImage(drawingOff,sx,sy,2*r,2*r,dx,dy,2*r,2*r);
 cxt.restore(); 
 }
 }
 } 
}
</script>

<canvas id="drawing1" >
 <p>The canvas element is not supported!</p>
</canvas>
<canvas id="drawing2" >
 <p>The canvas element is not supported!</p>
</canvas>
<br>
<button id="noGreen">无绿色</button>
<button id="noBlue">无蓝色</button>
<button id="toGrey">灰度</button>
<button id="toBlackWhite">黑白</button>
<button id="reverse">反色</button>
<script>
if(drawing1.getContext){
 var cxt1 = drawing1.getContext('2d');
 var cxt2 = drawing2.getContext('2d');
 var img = new Image();
 img.src="chunfen.jpg";
 img.onload = function(){
 cxt1.drawImage(img,0,0);
 function filter(fn){
 var imageData = cxt1.getImageData(0,0,img.width,img.height); 
 cxt2.clearRect(0,0,drawing2.width,drawing2.height); 
 var data = imageData.data;
 for(var i = 0, len = data.length; i < len; i+=4){
 fn(data,i)
 }
 imageData.data = data;
 cxt2.putImageData(imageData,0,0); 
 }
 function fnNoGreen(data,i){
 data[i+1] = 0;
 }
 function fnNoBlue(data,i){
 data[i+2] = 0;
 } 
 function fnReverse(data,i){
 var red = data[i];
 var green = data[i+1];
 var blue = data[i+2];
 var alpha = data[i+3];
 data[i] = 255 - red;
 data[i+1] = 255 - green;
 data[i+2] = 255 - blue;
 } 
 function fnToGrey(data,i){
 var red = data[i];
 var green = data[i+1];
 var blue = data[i+2];
 var alpha = data[i+3];
 var average = Math.floor((red+green+blue)/3);
 data[i] = data[i+1] = data[i+2] = average; 
 } 
 function fnToBlackWhite(data,i){
 var red = data[i];
 var green = data[i+1];
 var blue = data[i+2];
 var alpha = data[i+3];
 var average = Math.floor((red+green+blue)/3);
 if(average > 255/2){
 var result = 255;
 }else{
 var result = 0;
 }
 data[i] = data[i+1] = data[i+2] = result; 
 }
 toGrey.onclick = function(){
 filter(fnToGrey);
 }
 noGreen.onclick = function(){
 filter(fnNoGreen);
 } 
 noBlue.onclick = function(){
 filter(fnNoBlue);
 } 
 toBlackWhite.onclick = function(){
 filter(fnToBlackWhite);
 }
 reverse.onclick = function(){
 filter(fnReverse);
 } 
 }
}
</script>

function fnToBlur(n){
 cxt2.clearRect(0,0,drawing2.width,drawing2.height); 
 var imageData = cxt1.getImageData(0,0,drawing2.width,drawing2.height); 
 var tempImageData = imageData;
 var data = imageData.data;
 var tempData = tempImageData.data;
 var blurR = n;
 var totalnum = (2*blurR + 1)*(2*blurR + 1);
 for(var i = blurR; i < drawing2.height - blurR; i++){
 for(var j = blurR; j < drawing2.width - blurR; j++){
 var totalr = 0, totalg = 0, totalb = 0;
 for(var dx = -blurR; dx <= blurR; dx++){
 for(var dy = -blurR; dy <= blurR; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 totalr += tempData[p*4+0];
 totalg += tempData[p*4+1];
 totalb += tempData[p*4+2];
 }
 }
 var p = i*drawing2.width + j;
 data[p*4+0] = totalr / totalnum;
 data[p*4+1] = totalg / totalnum;
 data[p*4+2] = totalb / totalnum;
 }
 }
 imageData.data = data;
 cxt2.putImageData(imageData,0,0); 
 }

function fnToMosaic(n){
 cxt2.clearRect(0,0,drawing2.width,drawing2.height); 
 var imageData = cxt1.getImageData(0,0,drawing2.width,drawing2.height); 
 var tempImageData = imageData;
 var data = imageData.data;
 var tempData = tempImageData.data;
 var size = n;
 var totalnum = size*size;
 for(var i = 0; i < drawing2.height; i+=size){
 for(var j = 0; j < drawing2.width; j+=size){
 var totalr = 0, totalg = 0, totalb = 0;
 for(var dx = 0; dx < size; dx++){
 for(var dy = 0; dy < size; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 totalr += tempData[p*4+0];
 totalg += tempData[p*4+1];
 totalb += tempData[p*4+2];
 }
 }
 var p = i*drawing2.width + j;
 var resr = totalr / totalnum;
 var resg = totalg / totalnum;
 var resb = totalb / totalnum;
 for(var dx = 0; dx < size; dx++){
 for(var dy = 0; dy < size; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 data[p*4+0]= resr;
 data[p*4+1]= resg;
 data[p*4+2]= resb;
 }
 }
 }
 }
 imageData.data = data;
 cxt2.putImageData(imageData,0,0); 
 }

<canvas id="drawing1" >
 <p>The canvas element is not supported!</p>
</canvas>
<canvas id="drawing2" >
 <p>The canvas element is not supported!</p>
</canvas>
<br>
<button id="toLightBlur">轻度模糊</button>
<button id="toHeavyBlur">重度模糊</button>
<button id="toLightMosaic">轻度马赛克</button>
<button id="toHeavyMosaic">重度马赛克</button>
<script>
if(drawing1.getContext){
 var cxt1 = drawing1.getContext('2d');
 var cxt2 = drawing2.getContext('2d');
 var img = new Image();
 img.src="chunfen.jpg";
 img.onload = function(){
 cxt1.drawImage(img,0,0);
 toLightBlur.onclick = function(){
 fnToBlur(1);
 }
 toHeavyBlur.onclick = function(){
 fnToBlur(3);
 } 
 toLightMosaic.onclick = function(){
 fnToMosaic(4);
 } 
 toHeavyMosaic.onclick = function(){
 fnToMosaic(9);
 } 
 function fnToBlur(n){
 cxt2.clearRect(0,0,drawing2.width,drawing2.height); 
 var imageData = cxt1.getImageData(0,0,drawing2.width,drawing2.height); 
 var tempImageData = imageData;
 var data = imageData.data;
 var tempData = tempImageData.data;
 var blurR = n;
 var totalnum = (2*blurR + 1)*(2*blurR + 1);
 for(var i = blurR; i < drawing2.height - blurR; i++){
 for(var j = blurR; j < drawing2.width - blurR; j++){
 var totalr = 0, totalg = 0, totalb = 0;
 for(var dx = -blurR; dx <= blurR; dx++){
 for(var dy = -blurR; dy <= blurR; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 totalr += tempData[p*4+0];
 totalg += tempData[p*4+1];
 totalb += tempData[p*4+2];
 }
 }
 var p = i*drawing2.width + j;
 data[p*4+0] = totalr / totalnum;
 data[p*4+1] = totalg / totalnum;
 data[p*4+2] = totalb / totalnum;
 }
 }
 imageData.data = data;
 cxt2.putImageData(imageData,0,0); 
 }
 function fnToMosaic(n){
 cxt2.clearRect(0,0,drawing2.width,drawing2.height); 
 var imageData = cxt1.getImageData(0,0,drawing2.width,drawing2.height); 
 var tempImageData = imageData;
 var data = imageData.data;
 var tempData = tempImageData.data;
 var size = n;
 var totalnum = size*size;
 for(var i = 0; i < drawing2.height; i+=size){
 for(var j = 0; j < drawing2.width; j+=size){
 var totalr = 0, totalg = 0, totalb = 0;
 for(var dx = 0; dx < size; dx++){
 for(var dy = 0; dy < size; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 totalr += tempData[p*4+0];
 totalg += tempData[p*4+1];
 totalb += tempData[p*4+2];
 }
 }
 var p = i*drawing2.width + j;
 var resr = totalr / totalnum;
 var resg = totalg / totalnum;
 var resb = totalb / totalnum;
 for(var dx = 0; dx < size; dx++){
 for(var dy = 0; dy < size; dy++){
 var x = i + dx;
 var y = j + dy;
 var p = x*drawing2.width + y;
 data[p*4+0]= resr;
 data[p*4+1]= resg;
 data[p*4+2]= resb;
 }
 }
 }
 }
 imageData.data = data;
 cxt2.putImageData(imageData,0,0); 
 } 
 }
}
</script>