js-dicom/src/ImageUtility/generateLut.js

this is js-dicom

import internal from './internal';

function generateLutNew(image, windowWidth, windowCenter, invert, modalityLUT, voiLUT)
{
    if(image.lut === undefined) {
        image.lut =  new Int16Array(image.maxPixelValue - Math.min(image.minPixelValue,0)+1);
    }
    var lut = image.lut;
    var maxPixelValue = image.maxPixelValue;
    var minPixelValue = image.minPixelValue;

    var mlutfn = internal.getModalityLUT(image.slope, image.intercept, modalityLUT);
    var vlutfn = internal.getVOILUT(windowWidth, windowCenter, voiLUT);

    var offset = 0;
    if(minPixelValue < 0) {
        offset = minPixelValue;
    }
    var storedValue;
    var modalityLutValue;
    var voiLutValue;
    var clampedValue;

    for(storedValue = image.minPixelValue; storedValue <= maxPixelValue; storedValue++)
    {
        modalityLutValue = mlutfn(storedValue);
        voiLutValue = vlutfn(modalityLutValue);
        clampedValue = Math.min(Math.max(voiLutValue, 0), 255);
        if(!invert) {
            lut[storedValue+ (-offset)] = Math.round(clampedValue);
        } else {
            lut[storedValue + (-offset)] = Math.round(255 - clampedValue);
        }
    }
    return lut;
}



/**
 * Creates a LUT used while rendering to convert stored pixel values to
 * display pixels
 *
 * @param image
 * @returns {Array}
 */
function generateLut(image, windowWidth, windowCenter, invert, modalityLUT, voiLUT)
{
    if(modalityLUT || voiLUT) {
        return generateLutNew(image, windowWidth, windowCenter, invert, modalityLUT, voiLUT);
    }

    if(image.lut === undefined) {
        image.lut =  new Int16Array(image.maxPixelValue - Math.min(image.minPixelValue,0)+1);
    }
    var lut = image.lut;

    var maxPixelValue = image.maxPixelValue;
    var minPixelValue = image.minPixelValue;
    var slope = image.slope;
    var intercept = image.intercept;
    var localWindowWidth = windowWidth;
    var localWindowCenter = windowCenter;
    var modalityLutValue;
    var voiLutValue;
    var clampedValue;
    var storedValue;

    // NOTE: As of Nov 2014, most javascript engines have lower performance when indexing negative indexes.
    // We improve performance by offsetting the pixel values for signed data to avoid negative indexes
    // when generating the lut and then undo it in storedPixelDataToCanvasImagedata.  Thanks to @jpambrun
    // for this contribution!

    var offset = 0;
    if(minPixelValue < 0) {
        offset = minPixelValue;
    }

    if(invert === true) {
        for(storedValue = image.minPixelValue; storedValue <= maxPixelValue; storedValue++)
        {
            modalityLutValue =  storedValue * slope + intercept;
            voiLutValue = (((modalityLutValue - (localWindowCenter)) / (localWindowWidth) + 0.5) * 255.0);
            clampedValue = Math.min(Math.max(voiLutValue, 0), 255);
            lut[storedValue + (-offset)] = Math.round(255 - clampedValue);
        }
    }
    else {
        for(storedValue = image.minPixelValue; storedValue <= maxPixelValue; storedValue++)
        {
            modalityLutValue = storedValue * slope + intercept;
            voiLutValue = (((modalityLutValue - (localWindowCenter)) / (localWindowWidth) + 0.5) * 255.0);
            clampedValue = Math.min(Math.max(voiLutValue, 0), 255);
            lut[storedValue+ (-offset)] = Math.round(clampedValue);
        }
    }
}

export default  generateLut;