78 lines
2.2 KiB
HTML
78 lines
2.2 KiB
HTML
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<title>In-Browser Greyscale converter</title>
|
|
<meta charset="utf-8" />
|
|
<meta http-equiv="X-UA-Compatible" content="IE=edge">
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|
<style>
|
|
canvas {
|
|
border: 1px dashed black;
|
|
width: 400px;
|
|
height: 400px;
|
|
}
|
|
#original {
|
|
display:none;
|
|
}
|
|
</style>
|
|
|
|
<body>
|
|
<input type=file name=file id=file @change=${ele._onFileChange}/>
|
|
<canvas id=original></canvas>
|
|
|
|
<canvas id=grey></canvas>
|
|
|
|
<script type="text/javascript" charset="utf-8">
|
|
function drawImageAndGreyscaleImg(img) {
|
|
const oCanvas = document.querySelector('#original');
|
|
oCanvas.width = img.width;
|
|
oCanvas.height = img.height;
|
|
const oCtx = oCanvas.getContext('2d');
|
|
|
|
oCtx.drawImage(img, 0, 0);
|
|
|
|
const pixels = oCtx.getImageData(0, 0, img.width, img.height).data;
|
|
|
|
const gCanvas = document.querySelector('#grey');
|
|
gCanvas.width = img.width;
|
|
gCanvas.height = img.height;
|
|
const gCtx = gCanvas.getContext('2d');
|
|
|
|
for (let y = 0; y < img.height; y++) {
|
|
for (let x = 0; x < img.width; x++) {
|
|
const offset = 4*(x + img.width*y)
|
|
const r = pixels[offset], g = pixels[offset + 1],
|
|
b = pixels[offset + 2], a = pixels[offset + 3];
|
|
const grey = a*(r + g + b)/3;
|
|
pixels[offset ] = grey;
|
|
pixels[offset + 1] = grey;
|
|
pixels[offset + 2] = grey;
|
|
}
|
|
}
|
|
|
|
const greyData = new ImageData(pixels, img.width, img.height);
|
|
|
|
gCtx.putImageData(greyData, 0, 0);
|
|
}
|
|
document.querySelector('#file').addEventListener('change', (e) => {
|
|
const toLoad = e.target.files[0];
|
|
const reader = new FileReader();
|
|
reader.addEventListener('load', () => {
|
|
const b64dataURL = reader.result;
|
|
|
|
const img = new Image();
|
|
img.src = b64dataURL;
|
|
requestAnimationFrame( () => {
|
|
drawImageAndGreyscaleImg(img);
|
|
});
|
|
|
|
});
|
|
reader.addEventListener('error', () => {
|
|
console.error('Failed to load '+ toLoad.name);
|
|
});
|
|
reader.readAsDataURL(toLoad);
|
|
});
|
|
</script>
|
|
<body>
|
|
</html>
|