js-dicom/src/ImageUtility/metaData/getModalityLUTOutputPixelRepresentation.js

this is js-dicom

/* eslint no-bitwise: 0 */

function getMinStoredPixelValue (dataSet) {
    const pixelRepresentation = dataSet.uint16('x00280103');
    const bitsStored = dataSet.uint16('x00280101');

    if (pixelRepresentation === 0) {
        return 0;
    }

    return -1 << (bitsStored - 1);
}

// 0 = unsigned / US, 1 = signed / SS
function getModalityLUTOutputPixelRepresentation (dataSet) {

    // CT SOP Classes are always signed
    const sopClassUID = dataSet.string('x00080016');

    if (sopClassUID === '1.2.840.10008.5.1.4.1.1.2' ||
        sopClassUID === '1.2.840.10008.5.1.4.1.1.2.1') {
        return 1;
    }

    // if rescale intercept and rescale slope are present, pass the minimum stored
    // pixel value through them to see if we get a signed output range
    const rescaleIntercept = dataSet.floatString('x00281052');
    const rescaleSlope = dataSet.floatString('x00281053');

    if (rescaleIntercept !== undefined && rescaleSlope !== undefined) {
        const minStoredPixelValue = getMinStoredPixelValue(dataSet); //
        const minModalityLutValue = minStoredPixelValue * rescaleSlope + rescaleIntercept;

        if (minModalityLutValue < 0) {
            return 1;
        }

        return 0;

    }

    // Output of non linear modality lut is always unsigned
    if (dataSet.elements.x00283000 && dataSet.elements.x00283000.length > 0) {
        return 0;
    }

    // If no modality lut transform, output is same as pixel representation
    return dataSet.uint16('x00280103');
}

export default getModalityLUTOutputPixelRepresentation;