pirosuke/index.html

## index.html
<html>
    <head>
        <title>OpenCV.js Test</title>
    </head>
    <body>
        <table>
            <tr>
                <th>source</th>
                <th>output</th>
            </tr>
            <tr>
                <td>
                    <img src="./lena.jpg" id="src-image" style="width: 400px;" />
                    <img id="hidden-image" src="./lena.jpg" style="display: none;" />
                </td>
                <td>
                    <canvas id="dest-canvas"></canvas>
                    <canvas id="hidden-canvas" style="display: none;"></canvas>
                </td>
            </tr>
            <tr>
                <td>
                    <input type="file" id="input-file" />
                </td>
                <td>
                    <input type="button" value="グレースケール化" id="gray-scale-btn" />
                    <input type="button" value="線画化" id="linedraw-btn" />
                    <a href="#" id="download-btn" download="converted.png">ダウンロード</a>
                </td>
            </tr>
        </table>

        <script src="./opencv.js" type="text/javascript"></script>
        <script src="./index.js" type="text/javascript"></script>
    </body>
</html>

## index.js
const srcImg = document.getElementById('src-image');
const hiddenImg = document.getElementById('hidden-image');
const fileInput = document.getElementById('input-file');
const canvas = document.getElementById('dest-canvas');
const hiddenCanvas = document.getElementById('hidden-canvas');
const grayScaleBtn = document.getElementById('gray-scale-btn');
const lineDrawBtn = document.getElementById('linedraw-btn');
const downloadBtn = document.getElementById('download-btn');

function convertImageToGray(img) {
    let dst = new cv.Mat();
    cv.cvtColor(img, dst, cv.COLOR_RGBA2GRAY, 0);
    return dst;
}

function convertImageToLineDrawing(img) {
    const kernel = cv.getStructuringElement(cv.MORPH_RECT,new cv.Size(5,5));

    const imgGray = new cv.Mat();
    cv.cvtColor(img, imgGray, cv.COLOR_RGBA2GRAY);

    const imgDilated = new cv.Mat();
    cv.dilate(imgGray, imgDilated, kernel, new cv.Point(-1, 1), 1);

    const imgDiff = new cv.Mat();
    cv.absdiff(imgDilated, imgGray, imgDiff);

    const contour = new cv.Mat();
    cv.bitwise_not(imgDiff, contour);
    return contour;
}

function dataUriToBlob(dataUri) {
    const b64 = atob(dataUri.split(',')[1]);
    const u8 = Uint8Array.from(b64.split(''), e => e.charCodeAt());
    return new Blob([u8], {type: 'image/png'});
}

fileInput.addEventListener('change', e => {
    srcImg.src = URL.createObjectURL(e.target.files[0]);
    hiddenImg.src = URL.createObjectURL(e.target.files[0]);
}, false);

grayScaleBtn.addEventListener('click', e => {
    let src = cv.imread(srcImg);
    const dst = convertImageToGray(src);
    cv.imshow('dest-canvas', dst);
    src.delete();
    dst.delete();

    let hiddenSrc = cv.imread(hiddenImg);
    const hiddenDst = convertImageToGray(hiddenSrc);
    cv.imshow('hidden-canvas', hiddenDst);
    hiddenSrc.delete();
    hiddenDst.delete();
});

lineDrawBtn.addEventListener('click', e => {
    const src = cv.imread(srcImg);
    const dst = convertImageToLineDrawing(src);
    cv.imshow('dest-canvas', dst);
    src.delete();
    dst.delete();

    const hiddenSrc = cv.imread(hiddenImg);
    const hiddenDst = convertImageToLineDrawing(hiddenSrc);
    cv.imshow('hidden-canvas', hiddenDst);
    hiddenSrc.delete();
    hiddenDst.delete();
});

downloadBtn.addEventListener('click', e => {
    const data = hiddenCanvas.toDataURL();
    const url = URL.createObjectURL(dataUriToBlob(data));
    downloadBtn.href = url;
});
	<html>
	<head>
	<title>OpenCV.js Test</title>
	</head>
	<body>
	<table>
	<tr>
	<th>source</th>
	<th>output</th>
	</tr>
	<tr>
	<td>
	<img src="./lena.jpg" id="src-image" style="width: 400px;" />
	<img id="hidden-image" src="./lena.jpg" style="display: none;" />
	</td>
	<td>
	<canvas id="dest-canvas"></canvas>
	<canvas id="hidden-canvas" style="display: none;"></canvas>
	</td>
	</tr>
	<tr>
	<td>
	<input type="file" id="input-file" />
	</td>
	<td>
	<input type="button" value="グレースケール化" id="gray-scale-btn" />
	<input type="button" value="線画化" id="linedraw-btn" />
	<a href="#" id="download-btn" download="converted.png">ダウンロード</a>
	</td>
	</tr>
	</table>

	<script src="./opencv.js" type="text/javascript"></script>
	<script src="./index.js" type="text/javascript"></script>
	</body>
	</html>
	const srcImg = document.getElementById('src-image');
	const hiddenImg = document.getElementById('hidden-image');
	const fileInput = document.getElementById('input-file');
	const canvas = document.getElementById('dest-canvas');
	const hiddenCanvas = document.getElementById('hidden-canvas');
	const grayScaleBtn = document.getElementById('gray-scale-btn');
	const lineDrawBtn = document.getElementById('linedraw-btn');
	const downloadBtn = document.getElementById('download-btn');

	function convertImageToGray(img) {
	let dst = new cv.Mat();
	cv.cvtColor(img, dst, cv.COLOR_RGBA2GRAY, 0);
	return dst;
	}

	function convertImageToLineDrawing(img) {
	const kernel = cv.getStructuringElement(cv.MORPH_RECT,new cv.Size(5,5));

	const imgGray = new cv.Mat();
	cv.cvtColor(img, imgGray, cv.COLOR_RGBA2GRAY);

	const imgDilated = new cv.Mat();
	cv.dilate(imgGray, imgDilated, kernel, new cv.Point(-1, 1), 1);

	const imgDiff = new cv.Mat();
	cv.absdiff(imgDilated, imgGray, imgDiff);

	const contour = new cv.Mat();
	cv.bitwise_not(imgDiff, contour);
	return contour;
	}

	function dataUriToBlob(dataUri) {
	const b64 = atob(dataUri.split(',')[1]);
	const u8 = Uint8Array.from(b64.split(''), e => e.charCodeAt());
	return new Blob([u8], {type: 'image/png'});
	}

	fileInput.addEventListener('change', e => {
	srcImg.src = URL.createObjectURL(e.target.files[0]);
	hiddenImg.src = URL.createObjectURL(e.target.files[0]);
	}, false);

	grayScaleBtn.addEventListener('click', e => {
	let src = cv.imread(srcImg);
	const dst = convertImageToGray(src);
	cv.imshow('dest-canvas', dst);
	src.delete();
	dst.delete();

	let hiddenSrc = cv.imread(hiddenImg);
	const hiddenDst = convertImageToGray(hiddenSrc);
	cv.imshow('hidden-canvas', hiddenDst);
	hiddenSrc.delete();
	hiddenDst.delete();
	});

	lineDrawBtn.addEventListener('click', e => {
	const src = cv.imread(srcImg);
	const dst = convertImageToLineDrawing(src);
	cv.imshow('dest-canvas', dst);
	src.delete();
	dst.delete();

	const hiddenSrc = cv.imread(hiddenImg);
	const hiddenDst = convertImageToLineDrawing(hiddenSrc);
	cv.imshow('hidden-canvas', hiddenDst);
	hiddenSrc.delete();
	hiddenDst.delete();
	});

	downloadBtn.addEventListener('click', e => {
	const data = hiddenCanvas.toDataURL();
	const url = URL.createObjectURL(dataUriToBlob(data));
	downloadBtn.href = url;
	});