js-dicom/src/ImageUtility/colorSpaceConverters/convertPALETTECOLOR.js

this is js-dicom

/* eslint no-bitwise: 0 */

export default function (imageFrame, rgbaBuffer) {
    const numPixels = imageFrame.columns * imageFrame.rows;
    let palIndex = 0;
    let rgbaIndex = 0;
    const pixelData = imageFrame.pixelData;
    const start = imageFrame.redPaletteColorLookupTableDescriptor[1];
    const rData = imageFrame.redPaletteColorLookupTableData;
    const gData = imageFrame.greenPaletteColorLookupTableData;
    const bData = imageFrame.bluePaletteColorLookupTableData;
    const shift = imageFrame.redPaletteColorLookupTableDescriptor[2] === 8 ? 0 : 8;
    let len = imageFrame.redPaletteColorLookupTableData.length;

    if (len === 0) {
        len = 65535;
    }

    for (let i = 0; i < numPixels; ++i) {
        let value = pixelData[palIndex++];

        if (value < start) {
            value = 0;
        } else if (value > start + len - 1) {
            value = len - 1;
        } else {
            value -= start;
        }

        rgbaBuffer[rgbaIndex++] = rData[value] >> shift;
        rgbaBuffer[rgbaIndex++] = gData[value] >> shift;
        rgbaBuffer[rgbaIndex++] = bData[value] >> shift;
        rgbaBuffer[rgbaIndex++] = 255;
    }
}