how to change the color of an image in a HTML5 Can

问题:

I want to change the background color of this image while keeping the form, the effects and the contour of the image.

<canvas id="canvas01" width="1200" height="800"></canvas>
<script>
    function drawImage(imageObj,x, y, width, height){
        var canvas = document.getElementById('canvas01');
        var context = canvas.getContext('2d');
        context.drawImage(imageObj, x, y, width, height);
    }
    var image = new Image();
    image.onload = function(){
        drawImage(this, 400, 100, 320, 450);
    };
    image.src ="images/658FFBC6.png";
</script>

回答1:

Luma preservation

At the risk of looking similar to the existing answer, I would like to point out a small but important difference using a slightly different approach.

The key is to preserve the luma component in an image (ie. shadow details, wrinkles etc. in this case) so two steps are needed to control the look using blending modes via globalCompositeOperation (or alternatively, a manual approach using conversion between RGB and the HSL color-space if older browsers must be supported):

• "saturation": will alter the chroma (intensity, saturation) from the next drawn element and apply it to the existing content on the canvas, but preserve luma and hue.
• "hue": will grab the chroma and luma from the source but alter the hue, or color if you will, based on the next drawn element.

As these are blending modes (ignoring the alpha channel) we will also need to clip the result using composition as a last step.

The color blending mode can be used too but it will alter luma which may or may not be desirable. The difference can be subtle in many cases, but also very obvious depending on target chroma and hue where luma/shadow definition is lost.

So, to achieve a good quality result preserving both luma and chroma, these are more or less the main steps (assumes an empty canvas):

// step 1: draw in original image
ctx.globalCompositeOperation = "source-over";
ctx.drawImage(img, 0, 0);

// step 2: adjust saturation (chroma, intensity)
ctx.globalCompositeOperation = "saturation";
ctx.fillStyle = "hsl(0," + sat + "%, 50%)";  // hue doesn't matter here
ctx.fillRect(0, 0);

// step 3: adjust hue, preserve luma and chroma
ctx.globalCompositeOperation = "hue";
ctx.fillStyle = "hsl(" + hue + ",1%, 50%)";  // sat must be > 0, otherwise won't matter
ctx.fillRect(0, 0, c.width, c.height);

// step 4: in our case, we need to clip as we filled the entire area
ctx.globalCompositeOperation = "destination-in";
ctx.drawImage(img, 0, 0);

// step 5: reset comp mode to default
ctx.globalCompositeOperation = "source-over";

50% lightness (L) will keep the original luma value.

Live Example

Click the checkbox to see the effect on the result. Then test with different chroma and hue settings.

var ctx = c.getContext("2d");
var img = new Image(); img.onload = demo; img.src = "//i.stack.imgur.com/Kk1qd.png";
function demo() {c.width = this.width>>1; c.height = this.height>>1; render()}

function render() {
  var hue = +rHue.value, sat = +rSat.value, l = +rL.value;
  
  ctx.clearRect(0, 0, c.width, c.height);
  ctx.globalCompositeOperation = "source-over";
  ctx.drawImage(img, 0, 0, c.width, c.height);

  if (!!cColor.checked) {
    // use color blending mode
    ctx.globalCompositeOperation = "color";
    ctx.fillStyle = "hsl(" + hue + "," + sat + "%, 50%)";
    ctx.fillRect(0, 0, c.width, c.height);
  }
  else {
    // adjust "lightness"
    ctx.globalCompositeOperation = l < 100 ? "color-burn" : "color-dodge";
    // for common slider, to produce a valid value for both directions
    l = l >= 100 ? l - 100 : 100 - (100 - l);
    ctx.fillStyle = "hsl(0, 50%, " + l + "%)";
    ctx.fillRect(0, 0, c.width, c.height);
    
    // adjust saturation
    ctx.globalCompositeOperation = "saturation";
    ctx.fillStyle = "hsl(0," + sat + "%, 50%)";
    ctx.fillRect(0, 0, c.width, c.height);

    // adjust hue
    ctx.globalCompositeOperation = "hue";
    ctx.fillStyle = "hsl(" + hue + ",1%, 50%)";
    ctx.fillRect(0, 0, c.width, c.height);
  }
  
  // clip
  ctx.globalCompositeOperation = "destination-in";
  ctx.drawImage(img, 0, 0, c.width, c.height);

  // reset comp. mode to default
  ctx.globalCompositeOperation = "source-over";
}

rHue.oninput = rSat.oninput = rL.oninput = cColor.onchange = render;

body {font:16px sans-serif}

<div>
  <label>Hue: <input type=range id=rHue max=359 value=0></label>
  <label>Saturation: <input type=range id=rSat value=100></label>
  <label>Lightness: <input type=range id=rL max=200 value=100></label>
  <label>Use "color" instead: <input type=checkbox id=cColor></label>
</div>
<canvas id=c></canvas>

回答2:

Global composite operations

The 2D context property ctx.globalCompositeOperation is very useful for a wide range of image processing tasks. For more on globalCompositeOperation at MDN

You can convert the image into a canvas, that way you can edit it.

function imageToCanvas(image){
    const c = document.createElement("canvas");
    c.width = image.width;
    c.height = image.height;
    c.ctx = c.getContext("2d"); // attach context to the canvas for eaasy reference
    c.ctx.drawImage(image,0,0);
    return c;
}

You can use the globalCompositeOperation = "color" to colour the image

function colorImage(image,color){ // image is a canvas image
     image.ctx.fillStyle = color;
     image.ctx.globalCompositeOperation = "color";
     image.ctx.fillRect(0,0,image.width,image.height);
     image.ctx.globalCompositeOperation = "source-over";
     return image;
}

Unfortunately this also overwrites the alpha pixels so you need to use the original image as a mask to restore the alpha pixels.

function maskImage(dest,source){
     dest.ctx.globalCompositeOperation = "destination-in";
     dest.ctx.drawImage(source,0,0);
     dest.ctx.globalCompositeOperation = "source-over";
     return dest;
}

And then you have a coloured image

Example.

In he example I colour the image in a range of colours and added a function to restore the canvas copy of the image back to the original. If you get the image from the page as an element then use naturalWidth and naturalHeight as the width and height properties may not match the image resolution.

const ctx = canvas.getContext("2d");
const image = new Image;
var colCopy;
image.src = "https://i.stack.imgur.com/Kk1qd.png";
image.onload = () => {
  colCopy = imageToCanvas(image);
  const scale = canvas.height / image.naturalHeight; 
  ctx.scale(scale, scale);
  ctx.drawImage(colCopy, 0, 0);
  for (var i = 32; i < 360; i += 32) {
    restoreImage(colCopy, image);
    colorImage(colCopy, "hsl(" + i + ",100%,50%)");
    maskImage(colCopy, image);
    ctx.drawImage(colCopy, 150 * i / 16, 0);
  }
}



function imageToCanvas(image) {
  const c = document.createElement("canvas");
  c.width = image.naturalWidth;
  c.height = image.naturalHeight;
  c.ctx = c.getContext("2d"); // attach context to the canvas for easy reference
  c.ctx.drawImage(image, 0, 0);
  return c;
}

function restoreImage(dest, source) {
  dest.ctx.clearRect(0, 0, dest.width, dest.height);
  dest.ctx.drawImage(source, 0, 0);
  return dest;
}

function colorImage(dest, color) { // image is a canvas image
  dest.ctx.fillStyle = color;
  dest.ctx.globalCompositeOperation = "color";
  dest.ctx.fillRect(0, 0, dest.width, dest.height);
  dest.ctx.globalCompositeOperation = "source-over";
  return dest;
}

function maskImage(dest, source) {
  dest.ctx.globalCompositeOperation = "destination-in";
  dest.ctx.drawImage(source, 0, 0);
  dest.ctx.globalCompositeOperation = "source-over";
  return dest;
}

canvas {
  border: 2px solid black;
}

<canvas id="canvas" width=600></canvas>

The image can get a little washed out in some situations, you can convert the image to a higher contrast black and white image using composite operations similar to shown above, and use the high contrast image as the template to colour.

Using Filters

Most of the common browsers now support canvas filters which has a hue shift filter. You can use that to shift the hue to the value you want, though first you will need to know what the image original hue is. (see below example on how to find HUE)

See Canvas filters at MDN for compatibility and how to use canvas filters.

The following function will preserve the saturation and just shift the hue.

// dest canvas to hold the resulting image
// source the original image
// hue The hue to set the dest image to
// sourceHue the hue reference point of the original image.
function colorImage(dest,source, hue , sourceHue) { // image is a canvas image
  dest.ctx.clearRect(0,0,dest.width, dest.height);
  dest.ctx.filter="hue-rotate("+((hue - sourceHue) | 0)+"deg)";
  dest.ctx.drawImage(source,0, 0, dest.width, dest.height);
  return dest;
}

Filters example.

The following uses ctx.filter = "hue-rotate(30deg)" to rotate the hue. I have not included any code to find the image original hue so manually set it by eye to 120.

const ctx = canvas.getContext("2d");
const image = new Image;
var colCopy;
const sourceHue = 120;
image.src = "https://i.stack.imgur.com/Kk1qd.png";
image.onload = () => {
  colCopy = imageToCanvas(image);
  
  const scale = canvas.height / image.naturalHeight; 
  ctx.scale(scale, scale);
  ctx.drawImage(colCopy, 0, 0);
  for (var i = 32; i < 360; i += 32) {
    colorImage(colCopy,image,i,sourceHue);
    ctx.drawImage(colCopy, 150 * i / 16, 0);
  }
}



function imageToCanvas(image) {
  const c = document.createElement("canvas");
  c.width = image.naturalWidth;
  c.height = image.naturalHeight;
  c.ctx = c.getContext("2d"); // attach context to the canvas for easy reference
  c.ctx.drawImage(image, 0, 0);
  return c;
}

function colorImage(dest,source, hueRotate , sourceHue) { // image is a canvas image
  dest.ctx.clearRect(0,0,dest.width, dest.height);
  dest.ctx.filter="hue-rotate("+((hueRotate - sourceHue) | 0)+"deg)";
  dest.ctx.drawImage(source,0, 0, dest.width, dest.height);
  return dest;
}

canvas {
  border: 2px solid black;
}

<canvas id="canvas" width=600></canvas>

RGB to Hue

There are plenty of answers to help find the hue of a pixel here on SO. Here is a particularly detailed one RGB to HSL conversion Don't forget to upvote the answer if you find it useful.

Filters example White.

The following uses ctx.filter = "grayscale(100%)" to remove saturation and then ctx.filter = "brightness(amount%)" to change the brightness. This gives a range of gray colours from black to white. You can also do the same with the colour, by reducing the grayscale amount.

const ctx = canvas.getContext("2d");
const image = new Image;
var colCopy;
const sourceHue = 120;
image.src = "https://i.stack.imgur.com/Kk1qd.png";
image.onload = () => {
  colCopy = imageToCanvas(image);
  
  const scale = canvas.height / image.naturalHeight; 
  ctx.scale(scale, scale);
  ctx.drawImage(colCopy, 0, 0);
  for (var i = 40; i < 240; i += 20) {
    grayImage(colCopy,image,i);
    ctx.drawImage(colCopy, 150 * ((i-40) / 12), 0);
  }
}



function imageToCanvas(image) {
  const c = document.createElement("canvas");
  c.width = image.naturalWidth;
  c.height = image.naturalHeight;
  c.ctx = c.getContext("2d"); // attach context to the canvas for easy reference
  c.ctx.drawImage(image, 0, 0);
  return c;
}

function grayImage(dest,source, brightness) { // image is a canvas image
  dest.ctx.clearRect(0,0,dest.width, dest.height);
  dest.ctx.filter = "grayscale(100%)";
  dest.ctx.drawImage(source,0, 0, dest.width, dest.height);
  dest.ctx.filter = "brightness(" + brightness +"%)";
  dest.ctx.drawImage(dest,0, 0, dest.width, dest.height);

  return dest;
}

canvas {
  border: 2px solid black;
}

<canvas id="canvas" width=600></canvas>