svg filter to make translucent pixels opaque?

Question

How would I create a svg filter to map all translucent pixels to opaque pixels? All transparent pixels should remain transparent.

I am trying to create a shape mask but need the edges of the masks to be fully opaque. Otherwise I am left with a halo when I use the mask. Here is an example of the halo I am trying to remove with this SVG filter: https://codepen.io/jedierikb/pen/yGYqKK

This answer here does something similar - setting all translucent pixels to transparent pixels using a feComponentTransfer.

Suggestions?

Answer 1

Just for comparison with Paul's answer, here is a filter with type="linear" slope="255"

var ctx = canvas.getContext('2d');
ctx.fillStyle = '#ABEDBE';
ctx.fillRect(0,0,canvas.width,canvas.height);
ctx.fillStyle = 'black';
ctx.font = '14px sans-serif';
ctx.textAlign = 'center';

// first without filter
ctx.fillText('no filter', 60, 20);
drawArc();
drawTriangle();
// then with filter
ctx.setTransform(1, 0, 0, 1, 120, 0);
ctx.filter = 'url(#remove-alpha)';
// and do the same ops
ctx.fillText('no alpha', 60, 20);
drawArc();
drawTriangle();

// to remove the filter
ctx.filter = 'none';


function drawArc() {
  ctx.beginPath();
  ctx.arc(60, 80, 50, 0, Math.PI * 2);
  ctx.stroke();
}

function drawTriangle() {
  ctx.beginPath();
  ctx.moveTo(60, 150);
  ctx.lineTo(110, 230);
  ctx.lineTo(10, 230);
  ctx.closePath();
  ctx.stroke();
}
// unrelated
// simply to show a zoomed-in version
var zCtx = zoomed.getContext('2d');
zCtx.imageSmoothingEnabled = false;
canvas.onmousemove = function drawToZoommed(e) {
  var x = e.pageX - this.offsetLeft,
    y = e.pageY - this.offsetTop,
    w = this.width,
    h = this.height;
    
  zCtx.clearRect(0,0,w,h);
  zCtx.drawImage(this, x-w/6,y-h/6,w, h, 0,0,w*3, h*3);
}

<svg width="0" height="0" style="position:absolute;z-index:-1;">
  <defs>
    <filter id="remove-alpha" x="0" y="0" width="100%" height="100%">
      <feComponentTransfer>
        <feFuncA type="linear" slope="255"></feFuncA>
      </feComponentTransfer>
      </filter>
  </defs>
</svg>

<canvas id="canvas" width="250" height="250" ></canvas>
<canvas id="zoomed" width="250" height="250" ></canvas>

Answer 2

Here's one way. All values of A except for 0 are set to 1 (opaque).

var ctx = canvas.getContext('2d');
ctx.fillStyle = '#ABEDBE';
ctx.fillRect(0,0,canvas.width,canvas.height);
ctx.fillStyle = 'black';
ctx.font = '14px sans-serif';
ctx.textAlign = 'center';

// first without filter
ctx.fillText('no filter', 60, 20);
drawArc();
drawTriangle();
// then with filter
ctx.setTransform(1, 0, 0, 1, 120, 0);
ctx.filter = 'url(#remove-alpha)';
// and do the same ops
ctx.fillText('no alpha', 60, 20);
drawArc();
drawTriangle();

// to remove the filter
ctx.filter = 'none';


function drawArc() {
  ctx.beginPath();
  ctx.arc(60, 80, 50, 0, Math.PI * 2);
  ctx.stroke();
}

function drawTriangle() {
  ctx.beginPath();
  ctx.moveTo(60, 150);
  ctx.lineTo(110, 230);
  ctx.lineTo(10, 230);
  ctx.closePath();
  ctx.stroke();
}
// unrelated
// simply to show a zoomed-in version
var zCtx = zoomed.getContext('2d');
zCtx.imageSmoothingEnabled = false;
canvas.onmousemove = function drawToZoommed(e) {
  var x = e.pageX - this.offsetLeft,
    y = e.pageY - this.offsetTop,
    w = this.width,
    h = this.height;
    
  zCtx.clearRect(0,0,w,h);
  zCtx.drawImage(this, x-w/6,y-h/6,w, h, 0,0,w*3, h*3);
}

<svg width="0" height="0" style="position:absolute;z-index:-1;">
  <defs>
    <filter id="remove-alpha" x="0" y="0" width="100%" height="100%">
      <feComponentTransfer>
        <feFuncA type="discrete" tableValues="0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                                              1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1"></feFuncA>
      </feComponentTransfer>
      </filter>
  </defs>
</svg>

<canvas id="canvas" width="250" height="250" ></canvas>
<canvas id="zoomed" width="250" height="250" ></canvas>