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preprocess.js
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preprocess.js
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// ==== gamma correction ====
var gamma = 2.2;
var gamma_invert = 1 / gamma;
function imgOrCanvasToLinear(img)
{
var inputImg, inputCtx, scaledCanvas;
if (!(img instanceof HTMLCanvasElement)){
inputImg = document.createElement('canvas');
inputImg.width = img.width;
inputImg.height = img.height;
inputCtx = inputImg.getContext('2d');
inputCtx.drawImage( img, 0, 0, img.width, img.height, 0, 0, img.width, img.height);
}
else{
inputImg = img;
inputCtx = inputImg.getContext('2d');
}
var inPixels = inputCtx.getImageData(0, 0, inputImg.width, inputImg.height).data;
// convert it to linear
var len = img.height*img.width*4;
var linearInPixel = {};//new Float32Array(len),
var gamma = 2.2
for (var pix = 0; pix < len; pix++)
{
linearInPixel[pix] = Math.pow(inPixels[pix], gamma);
}
return { data: linearInPixel, width: img.width, height: img.height, length : len};
}
function linearToImgCanvas(imgOutPut)
{
outputCanvas = document.createElement('canvas');
outputCanvas.width = imgOutPut.width;
outputCanvas.height = imgOutPut.height;
var outputCtx = outputCanvas.getContext('2d');
var outputPixels = outputCtx.getImageData( 0, 0, imgOutPut.width, imgOutPut.height );
var outputPixelsData = outputPixels.data;
for( var pix = 0; pix < imgOutPut.length; pix++ )
{
outputPixels.data[pix] = Math.pow(imgOutPut.data[pix], gamma_invert);
}
outputCtx.putImageData( outputPixels, 0, 0 );
return outputCanvas;
}
// ==== gamma correction ====
// ==== Lanczos resizing ====
//returns a function that calculates lanczos weight
function lanczosCreate(kernel){
return function(x){
if (x > kernel)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1
var xx = x / kernel;
return Math.sin(x) * Math.sin(xx) / x / xx;
}
}
function lancosCompute(linearImg, scale, kernel)
{
var w = ~~(linearImg.width*scale) + 1, h = ~~(linearImg.height*scale) + 1;
var linearOutput = { data: {}, width: w, height: h, length : w*h*4};
var lanczos = lanczosCreate(kernel);//lanczos3 if kernel === 3
var rcp_ratio = 2 / scale;
var range2 = Math.ceil(scale * kernel / 2);
var cacheLanc = {};
var center = {};
var icenter = {};
var u = 0;
while (++u < linearOutput.width) {
center.x = (u + 0.5) * scale;
icenter.x = Math.floor(center.x);
for (var v = 0; v < linearOutput.height; v++) {
center.y = (v + 0.5) * scale;
icenter.y = Math.floor(center.y);
var a, r, g, b, alpha;
a = r = g = b = alpha = 0;
for (var i = icenter.x - range2; i <= icenter.x + range2; i++) {
if (i < 0 || i >= linearImg.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - center.x));
if (!cacheLanc[f_x])
cacheLanc[f_x] = {};
for (var j = icenter.y - range2; j <= icenter.y + range2; j++) {
if (j < 0 || j >= linearImg.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - center.y));
if (cacheLanc[f_x][f_y] == undefined)
cacheLanc[f_x][f_y] = lanczos(Math.sqrt(Math.pow(f_x * rcp_ratio, 2) + Math.pow(f_y * rcp_ratio, 2)) / 1000);
weight = cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * linearImg.width + i) * 4;
a += weight;
r += weight * linearImg.data[idx];
g += weight * linearImg.data[idx + 1];
b += weight * linearImg.data[idx + 2];
alpha += weight * linearImg.data[idx + 3];
}
}
}
var idx = (v * linearOutput.width + u) * 4;
linearOutput.data[idx] = r / a;
linearOutput.data[idx + 1] = g / a;
linearOutput.data[idx + 2] = b / a;
linearOutput.data[idx + 3] = alpha / a;
}
}
return linearOutput;
}
//elem: img: image element, sx: scaled width, lobes: kernel radius
function thumbnailer(img, sx, lobes){
var linearImage = imgOrCanvasToLinear(img);
return linearToImgCanvas(lancosCompute(linearImage, sx / img.width, lobes));
}
// ==== Lanczos resizing ====
var fileinput = document.getElementById('fileinput');
var max_width = fileinput.getAttribute('data-maxwidth');
var max_height = fileinput.getAttribute('data-maxheight');
var preview = document.getElementById('preview');
var canvas = document.getElementById('canvas');
var form = document.getElementById('form');
function processfile(file) {
if( !( /image/i ).test( file.type ) )
{
alert( "File "+ file.name +" is not an image." );
return false;
}
// read the files
var reader = new FileReader();
reader.readAsArrayBuffer(file);
reader.onload = function (event) {
// blob stuff
var blob = new Blob([event.target.result]); // create blob...
window.URL = window.URL || window.webkitURL;
var blobURL = window.URL.createObjectURL(blob); // and get it's URL
// helper Image object
var image = new Image();
image.src = blobURL;
//preview.appendChild(image); // preview commented out, I am using the canvas instead
image.onload = function() {
// have to wait till it's loaded
//resized = resizeMe(image); // send it to canvas
var canvas = thumbnailer(image, max_width, 3);
var resized = canvas.toDataURL("image/jpeg",1.0);
preview.appendChild(canvas);
var newinput = document.createElement("input");
newinput.type = 'hidden'
newinput.name = 'images[]'
newinput.value = resized; // put result from canvas into new hidden input
form.appendChild(newinput);
}
};
}
function readfiles(files) {
// remove the existing canvases and hidden inputs if user re-selects new pics
var existinginputs = document.getElementsByName('images[]');
var existingcanvases = document.getElementsByTagName('canvas');
while (existinginputs.length > 0) { // it's a live list so removing the first element each time
// DOMNode.prototype.remove = function() {this.parentNode.removeChild(this);}
form.removeChild(existinginputs[0]);
preview.removeChild(existingcanvases[0]);
}
for (var i = 0; i < files.length; i++) {
processfile(files[i]); // process each file at once
}
fileinput.value = ""; //remove the original files from fileinput
// TODO remove the previous hidden inputs if user selects other files
}
// this is where it starts. event triggered when user selects files
fileinput.onchange = function(){
if ( !( window.File && window.FileReader && window.FileList && window.Blob ) ) {
alert('The File APIs are not fully supported in this browser.');
return false;
}
readfiles(fileinput.files);
}
// === RESIZE ====
function resizeMe(img) {
var canvas = document.createElement('canvas');
var width = img.width;
var height = img.height;
// calculate the width and height, constraining the proportions
if (width > height) {
if (width > max_width) {
//height *= max_width / width;
height = Math.round(height *= max_width / width);
width = max_width;
}
} else {
if (height > max_height) {
//width *= max_height / height;
width = Math.round(width *= max_height / height);
height = max_height;
}
}
// resize the canvas and draw the image data into it
canvas.width = width;
canvas.height = height;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, width, height);
canvas = thumbnailer(img, max_width, 3);
preview.appendChild(canvas); // do the actual resized preview
return canvas.toDataURL("image/jpeg",0.7); // get the data from canvas as 70% JPG (can be also PNG, etc.)
}