{"id":21,"date":"2012-05-04T22:58:31","date_gmt":"2012-05-04T22:58:31","guid":{"rendered":"http:\/\/beta.robertprice.co.uk\/robblog\/2012\/05\/extracting_and_drawing_part_of_an_image_into_an_html5_canvas-shtml\/"},"modified":"2012-05-04T22:58:31","modified_gmt":"2012-05-04T22:58:31","slug":"extracting_and_drawing_part_of_an_image_into_an_html5_canvas-shtml","status":"publish","type":"post","link":"https:\/\/www.robertprice.co.uk\/robblog\/extracting_and_drawing_part_of_an_image_into_an_html5_canvas-shtml\/","title":{"rendered":"Extracting And Drawing Part Of An Image Into An HTML5 Canvas"},"content":{"rendered":"

\nAs part of my Draw Something Solver, I need to be able to extract the letters from the screenshot image.\n<\/p>\n

\nI’ve already looked at loading an image into a HTML 5 canvas<\/a> object in an earlier post, so I will assume that code is already in place.\n<\/p>\n

\nIt’s actually very easy to extract part of an image from a canvas, we just need to use the getImageData()<\/code> method from the canvas context object. This takes 4 parameters, the x and y coordinates for the top left corner of the image, and width and height to extract.\n<\/p>\n

var letterImageData = dsCanvasContext.getImageData(27, 782, 72, 71);\n<\/pre>\n
\nIn this case, I’m cutting out a 72×71 block starting from the coordinates 27,782.\n<\/p>\n
\nIf you need to paste this extract into another canvas, or even the same canvas, you can use the putImageData<\/code> method on the canvas context object. This takes 3 parameters, the ImageData you wish to draw into the canvas, and the top left x and y coordinates to draw it into.\n<\/p>\n
dsCanvasContext.putImageData(letterImageData,0,0);<\/pre>\n
\nThis will post into the top left hand corner of the original canvas.<\/p>\n","protected":false},"excerpt":{"rendered":"
As part of my Draw Something Solver, I need to be able to extract the letters from the screenshot image. I’ve already looked at loading an image into a HTML 5 canvas object in an earlier post, so I will assume that code is already in place. It’s actually very easy to extract part of … Continue reading “Extracting And Drawing Part Of An Image Into An HTML5 Canvas”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[2],"tags":[24,31],"class_list":["post-21","post","type-post","status-publish","format-standard","hentry","category-dev","tag-html5","tag-javascript"],"yoast_head":"\nExtracting And Drawing Part Of An Image Into An HTML5 Canvas - Robert Price<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.robertprice.co.uk\/robblog\/extracting_and_drawing_part_of_an_image_into_an_html5_canvas-shtml\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Extracting And Drawing Part Of An Image Into An HTML5 Canvas - Robert Price\" \/>\n<meta property=\"og:description\" content=\"As part of my Draw Something Solver, I need to be able to extract the letters from the screenshot image. I’ve already looked at loading an image into a HTML 5 canvas object in an earlier post, so I will assume that code is already in place. 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