i have simple map static pixel image layer:
<!doctype html> <html> <head> <title>simple map</title> <link rel="stylesheet" href="http://openlayers.org/en/v3.13.0/css/ol.css" type="text/css"> <script src="http://openlayers.org/en/v3.13.0/build/ol.js"></script> // reference jquery here </head> <body> <div id="map" class="map"></div> <script> var extent = [0, 0, 2000000, 2000000]; var projection = new ol.proj.projection({ code: 'xkcd-image', units: 'pixels', extent: extent }); var map = new ol.map({ layers: [ new ol.layer.tile({ source: new ol.source.osm() }) ], target: 'map', view: new ol.view({ center: [0, 0], zoom: 2 }) }); image = new ol.layer.image({ source: new ol.source.imagestatic({ url: 'http://imgs.xkcd.com/comics/online_communities.png', projection: projection, imageextent: extent }) }); map.addlayer(image); image.on('singleclick', function(evt) { var xy = evt.pixel; console.log(xy); var canvascontext = $('.ol-unselectable')[0].getcontext('2d'); var pixelatclick = canvascontext.getimagedata(xy[0], xy[1], 1, 1).data; var red = pixelatclick[0]; // green [1] , blue [2] , alpha [4] }); </script> </body> </html> when clicking on image want color of pixel clicked on. far understand raster source example (http://openlayers.org/en/v3.13.0/examples/raster.html), possible raster sources converted image raster source. (when add raster source layer, message operation insecure, still use image show on map.)
here (how pixel's color value openlayers 3 layer?) color read evt.context. however, me evt.context undefined.
addendum: there might several image layers overlaying each other. need color single specific image layer.
so isn't ideal might send along right lines:
you can use pixel xy of click event query canvas object openlayers creates , puts map data onto.
map.on('singleclick', function(evt) { var xy = evt.pixel; var canvascontext = $('.ol-unselectable')[0].getcontext('2d'); var pixelatclick = canvascontext.getimagedata(xy[0], xy[1], 1, 1).data; var red = pixeatclick[0]; // green [1] , blue [2] , alpha [4] }); this assumes using jquery , canvas first dom element using class '.ol-unselectable'.
hope helps.
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