| Kevin Lubick | 42daf99 | 2019-04-19 11:58:56 -0400 | [diff] [blame^] | 1 | <!DOCTYPE html> |
| 2 | <html> |
| 3 | <head> |
| 4 | <title>In-Browser Greyscale converter</title> |
| 5 | <meta charset="utf-8" /> |
| 6 | <meta http-equiv="X-UA-Compatible" content="IE=edge"> |
| 7 | <meta name="viewport" content="width=device-width, initial-scale=1.0"> |
| 8 | <style> |
| 9 | canvas { |
| 10 | border: 1px dashed black; |
| 11 | width: 400px; |
| 12 | height: 400px; |
| 13 | } |
| 14 | #original { |
| 15 | display:none; |
| 16 | } |
| 17 | </style> |
| 18 | |
| 19 | <body> |
| 20 | <input type=file name=file id=file @change=${ele._onFileChange}/> |
| 21 | <canvas id=original></canvas> |
| 22 | |
| 23 | <canvas id=grey></canvas> |
| 24 | |
| 25 | <script type="text/javascript" charset="utf-8"> |
| 26 | function drawImageAndGreyscaleImg(img) { |
| 27 | const oCanvas = document.querySelector('#original'); |
| 28 | oCanvas.width = img.width; |
| 29 | oCanvas.height = img.height; |
| 30 | const oCtx = oCanvas.getContext('2d'); |
| 31 | |
| 32 | oCtx.drawImage(img, 0, 0); |
| 33 | |
| 34 | const pixels = oCtx.getImageData(0, 0, img.width, img.height).data; |
| 35 | |
| 36 | const gCanvas = document.querySelector('#grey'); |
| 37 | gCanvas.width = img.width; |
| 38 | gCanvas.height = img.height; |
| 39 | const gCtx = gCanvas.getContext('2d'); |
| 40 | |
| 41 | for (let y = 0; y < img.height; y++) { |
| 42 | for (let x = 0; x < img.width; x++) { |
| 43 | const offset = 4*(x + img.width*y) |
| 44 | const r = pixels[offset], g = pixels[offset + 1], b = pixels[offset + 2]; |
| 45 | const grey = (r + g + b)/3; |
| 46 | pixels[offset ] = grey; |
| 47 | pixels[offset + 1] = grey; |
| 48 | pixels[offset + 2] = grey; |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | const greyData = new ImageData(pixels, img.width, img.height); |
| 53 | |
| 54 | gCtx.putImageData(greyData, 0, 0); |
| 55 | } |
| 56 | document.querySelector('#file').addEventListener('change', (e) => { |
| 57 | const toLoad = e.target.files[0]; |
| 58 | const reader = new FileReader(); |
| 59 | reader.addEventListener('load', () => { |
| 60 | const b64dataURL = reader.result; |
| 61 | |
| 62 | const img = new Image(); |
| 63 | img.src = b64dataURL; |
| 64 | requestAnimationFrame( () => { |
| 65 | drawImageAndGreyscaleImg(img); |
| 66 | }); |
| 67 | |
| 68 | }); |
| 69 | reader.addEventListener('error', () => { |
| 70 | console.error('Failed to load '+ toLoad.name); |
| 71 | }); |
| 72 | reader.readAsDataURL(toLoad); |
| 73 | }); |
| 74 | </script> |
| 75 | <body> |
| 76 | </html> |