Silhouette a PNG image using CSS

Question

Anyone know of a way that I can get CSS to make a PNG image with transparency look completely blacked out like a silhouette?

In other words- Going from something li

Answer 1

I tried this code that uses a canvas, maybe you could refine it especially on lighter pixel inside the apple

<img id="canvasSource" src="apple.jpg" />

<br />

<canvas id="area" width="264" height="282"></canvas>

<!-- Javascript Code -->
<script type="text/javascript">
    window.onload = function() {
        var canvas = document.getElementById("area");
        var context = canvas.getContext("2d");
        var image = document.getElementById("canvasSource");
        context.drawImage(image, 0, 0);

        var imgd = context.getImageData(0, 0, 264, 282);
        var pix = imgd.data;
        var blackpixel = 21;
           for (var i = 0, n = pix.length; i < n; i += 4) {

            //console.log(pix[i], pix[i+1], pix[i+2]);
            if (i > 3) {
               if ((Math.abs(pix[i-3] - pix[i]) > 10) &&
                   (Math.abs(pix[i-2] - pix[i+1]) > 10) &&
                   (Math.abs(pix[i-1] - pix[i+2]) > 10)
                ) {

                   pix[i  ] = blackpixel;  
                   pix[i+1] = blackpixel;  
                   pix[i+2] = blackpixel;

               }
            }
            else {
               if (pix[i] < 250 && pix[i+1] < 250 && pix[i+2] < 250) {
                  pix[i  ] = blackpixel;  
                  pix[i+1] = blackpixel;  
                  pix[i+2] = blackpixel;
               }
         }

        }
        context.putImageData(imgd, 0, 0);       

    };
</script>

Answer 2

I don't see how it could be done with pure css. Javascript might be able to acheive it but you may consider using server side programming instead. With php you could make a duplicate of your original png on the server and replace the non-transparent pixels with a single color. It would be similar to a watermarking function.

Answer 3

Nowdays, filter combined to mix-blend-mode could do too :

span {/* to be used to lay the 'blender mask' over img */
  position: relative;
  display: inline-block;
  overflow:hidden;
}

span img {
  display: block;/* erase gap */
  max-width:45vw;
  filter: contrast(150%);
}
span + span img {
  filter: contrast(120%) saturate(0%);/* saturate(0%) is  similar to grayscale(100%) */
}

span:before {
  content: '';
  z-index: 1;
  height: 100%;
  background: white;
  position: absolute;
  top: 0;
  width: 100%;
  display: block;
  filter: contrast(10000%) brightness(0) saturate(100%) grayscale(100%);
  mix-blend-mode: color-burn;/* bake it to black */
  animation : span 2s infinite alternate;
}
@keyframes span {
  from{
    transform:translate(-100%,0)
  }
  25%,50% {
    transform:translate(0,0);
  }
  to{
    transform:translate(100%,0)
  }
}

<span><img src="https://i.stack.imgur.com/somZ7.jpg"/></span>
<span><img src="https://i.stack.imgur.com/somZ7.jpg"/></span>

Answer 4

You can apply to the image style like filter: contrast(0%) brightness(50%) to get a silhouette. Do not forget prefixes.