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Optimized JPG.js - reduced memory usage + 2.16x faster getLinearizedBlockData

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Linearize and scale the mcu blocks into the destination buffer in a single pass
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p01 2014-04-29 17:09:54 +02:00
parent 7067409e00
commit 287274d3dc
1 changed files with 17 additions and 42 deletions
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59
src/core/jpg.js
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@ -810,60 +810,35 @@ var JpegImage = (function jpegImage() {
_getLinearizedBlockData: function getLinearizedBlockData(width, height) {
var scaleX = this.width / width, scaleY = this.height / height;
var component, componentScaleX, componentScaleY;
var x, y, i;
var component, componentScaleX, componentScaleY, blocksPerScanline;
var x, y, i, j;
var index;
var offset = 0;
var Y, Cb, Cr, K, C, M, Ye, R, G, B;
var colorTransform;
var output;
var numComponents = this.components.length;
var dataLength = width * height * numComponents;
var data = new Uint8Array(dataLength);
var componentLine;
var xScaleBlockOffset = new Uint32Array(width);
var mask3LSB = 0xfffffff8; // used to clear the 3 LSBs
// lineData is reused for all components. Assume first component is
// the biggest
var lineData = new Uint8Array((this.components[0].blocksPerLine << 3) *
this.components[0].blocksPerColumn * 8);
// First construct image data ...
for (i = 0; i < numComponents; i++) {
component = this.components[i];
var blocksPerLine = component.blocksPerLine;
var blocksPerColumn = component.blocksPerColumn;
var samplesPerLine = blocksPerLine << 3;
var j, k, ll = 0;
var sample;
var lineOffset = 0;
for (var blockRow = 0; blockRow < blocksPerColumn; blockRow++) {
var scanLine = blockRow << 3;
for (var blockCol = 0; blockCol < blocksPerLine; blockCol++) {
var bufferOffset = getBlockBufferOffset(component,
blockRow, blockCol);
offset = 0;
sample = blockCol << 3;
for (j = 0; j < 8; j++) {
lineOffset = (scanLine + j) * samplesPerLine;
for (k = 0; k < 8; k++) {
lineData[lineOffset + sample + k] =
component.output[bufferOffset + offset++];
}
}
}
}
componentScaleX = component.scaleX * scaleX;
componentScaleY = component.scaleY * scaleY;
offset = i;
var cx, cy;
var index;
output = component.output;
blocksPerScanline = (component.blocksPerLine + 1) << 3;
// precalculate the xScaleBlockOffset
for (x = 0; x < width; x++) {
j = 0 | (x * componentScaleX);
xScaleBlockOffset[x] = ((j & mask3LSB) << 3) | (j & 7);
}
// linearize the blocks of the component
for (y = 0; y < height; y++) {
j = 0 | (y * componentScaleY);
index = blocksPerScanline * (j & mask3LSB) | ((j & 7) << 3);
for (x = 0; x < width; x++) {
cy = 0 | (y * componentScaleY);
cx = 0 | (x * componentScaleX);
index = cy * samplesPerLine + cx;
data[offset] = lineData[index];
data[offset] = output[index + xScaleBlockOffset[x]];
offset += numComponents;
}
}