js-dicom/src/ImageUtility/rendering/storedPixelDataToCanvasImageData.js

this is js-dicom

/**
 * This function transforms stored pixel values into a canvas image data buffer
 * by using a LUT.  This is the most performance sensitive code in cornerstone and
 * we use a special trick to make this go as fast as possible.  Specifically we
 * use the alpha channel only to control the luminance rather than the red, green and
 * blue channels which makes it over 3x faster.  The canvasImageDataData buffer needs
 * to be previously filled with white pixels.
 *
 * NOTE: Attribution would be appreciated if you use this technique!
 *
 * @param pixelData the pixel data
 * @param lut the lut
 * @param canvasImageDataData a canvasImgageData.data buffer filled with white pixels
 */
function storedPixelDataToCanvasImageData(image, lut, canvasImageDataData)
{
    var pixelData = image.getPixelData();
    var minPixelValue = image.minPixelValue;
    var canvasImageDataIndex = 3;
    var storedPixelDataIndex = 0;
    var localNumPixels = pixelData.length;
    var localPixelData = pixelData;
    var localLut = lut;
    var localCanvasImageDataData = canvasImageDataData;
    // NOTE: As of Nov 2014, most javascript engines have lower performance when indexing negative indexes.
    // We have a special code path for this case that improves performance.  Thanks to @jpambrun for this enhancement
    if(minPixelValue < 0){
        while(storedPixelDataIndex < localNumPixels) {
            localCanvasImageDataData[canvasImageDataIndex] = localLut[localPixelData[storedPixelDataIndex++] + (-minPixelValue)]; // alpha
            canvasImageDataIndex += 4;
        }
    }else{
        while(storedPixelDataIndex < localNumPixels) {
            localCanvasImageDataData[canvasImageDataIndex] = localLut[localPixelData[storedPixelDataIndex++]]; // alpha
            canvasImageDataIndex += 4;
        }
    }
}

export default storedPixelDataToCanvasImageData;