Quelle  trns-chunk.html   Sprache: HTML

<!DOCTYPE html>
<title>PNG test: tRNS chunk</title>
<link rel="help" href="https://w3c.github.io/PNG-spec/#11tRNS">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/html/canvas/resources/canvas-tests.js"></script>
<body>

<h1>tRNS chunk handling</h1>
<p class="desc">test ignored high bits on lower bit depth tRNS</p>

<p class="output">Actual output:</p>
<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>

<ul id="d"></ul>
<script>
var t = async_test("test ignored high bits on lower bit depth tRNS");
const img = new Image();
img.onload = () => {
  _addTest(function(canvas, ctx) {
    ctx.drawImage(img, 0, 0);

    var pixel = ctx.getImageData(5, 5, 1, 1, {colorSpace: "srgb"}).data;

    const pixel_expected = [255, 0, 0, 0];
    const epsilon = 2;

    _assertSame(pixel.length, pixel_expected.length, "pixel.length", "pixel_expected.length");
    // Ignore the color channel comparisons.
    // The image itself stores 255 red, 0 green, 0 blue.
    // But there may not be a requirement that this be preserved
    // while decoding or through canvas processing.
    assert_approx_equals(pixel[3], pixel_expected[3], epsilon);
  });
};
img.src = "support/trns-high-bits-set.png";
</script>