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added stepwise image downsampling to improve the resulting image quality #22

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added stepwise image downsampling to improve the resulting image quality #22

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23 changes: 20 additions & 3 deletions public/javascripts/imageupload.js
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,10 @@ angular.module('imageupload', [])

var canvas = getResizeArea();

var height = origImage.height;
var width = origImage.width;
var oheight = origImage.height;
var owidth = origImage.width;
var height = oheight;
var width = owidth;

// calculate the width and height, constraining the proportions
if (width > height) {
Expand All @@ -43,12 +45,27 @@ angular.module('imageupload', [])
}
}

var img = origImage;
// introduce downsampling steps if appropriate
if(oheight / height > 2) {
img = document.createElement('canvas');
var tctx = img.getContext("2d");
img.width = owidth;
img.height = oheight;
tctx.drawImage(origImage, 0, 0, owidth, oheight, 0, 0, owidth/2, oheight/2);
oheight /= 2; owidth /= 2;
while(oheight / height > 2) {
tctx.drawImage(img, 0, 0, owidth, oheight, 0, 0, owidth/2, oheight/2);
oheight /= 2; owidth /= 2;
}
}

canvas.width = width;
canvas.height = height;

//draw image on canvas
var ctx = canvas.getContext("2d");
ctx.drawImage(origImage, 0, 0, width, height);
ctx.drawImage(img, 0, 0, owidth, oheight, 0, 0, width, height);

// get the data from canvas as 70% jpg (or specified type).
return canvas.toDataURL(type, quality);
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