decodePixelData.js

const dcmjsImaging = require('dcmjs-imaging');

// Mimics a class not exported by dcmjs-imaging
const pixelShim = (
  width,
  height,
  bitsAllocated,
  bitsStored,
  samplesPerPixel,
  pixelRepresentation,
  planarConfiguration,
  photometricInterpretation
) => ({
  getWidth: () => width,
  getHeight: () => height,
  getBitsAllocated: () => bitsAllocated,
  getBitsStored: () => bitsStored,
  getSamplesPerPixel: () => samplesPerPixel,
  getPixelRepresentation: () => pixelRepresentation,
  getPlanarConfiguration: () => planarConfiguration,
  getPhotometricInterpretation: () => photometricInterpretation,
});

/**
 * Decodes frame pixel data.
 * @param {Object} dataset - The DICOM dataset object.
 * @param {string} transferSyntaxUid - The dataset transfer syntax UID.
 * @param {number} frame - The frame index.
 * @returns {Uint8Array} The decoded frame pixel data.
 */
const decodePixelData = (dataset, transferSyntaxUid, frame) => {
  if (frame < 0 || frame >= dataset.NumberOfFrames) {
    throw new Error(`Requested frame is out of range [${frame}]`);
  }
  if (!dataset.PixelData) {
    throw new Error('Could not extract pixel data');
  }
  if (!dataset.Columns || !dataset.Rows) {
    throw new Error(
      `Width/height has an invalid value [w: ${dataset.Columns}, h: ${dataset.Rows}]`
    );
  }
  if (!dataset.BitsAllocated || !dataset.BitsStored) {
    throw new Error(
      `Bits allocated/stored has an invalid value [allocated: ${dataset.BitsAllocated}, stored: ${dataset.BitsStored}]`
    );
  }
  if (!dataset.PhotometricInterpretation) {
    throw new Error(
      `Photometric interpretation has an invalid value [${dataset.PhotometricInterpretation}]`
    );
  }

  const pixelBuffers = dataset.PixelData;
  if (
    transferSyntaxUid === '1.2.840.10008.1.2' || // ImplicitVRLittleEndian
    transferSyntaxUid === '1.2.840.10008.1.2.1' || // ExplicitVRLittleEndian
    transferSyntaxUid === '1.2.840.10008.1.2.1.99' // DeflatedExplicitVRLittleEndian
  ) {
    const frameSize =
      dataset.Rows * dataset.Columns * dataset.SamplesPerPixel * ((dataset.BitsAllocated + 7) / 8);
    const frameOffset = frameSize * frame;
    const pixelBuffer = new Uint8Array(
      Array.isArray(pixelBuffers) ? pixelBuffers.find((o) => o) : pixelBuffers
    );
    const framePixelBuffer = pixelBuffer.slice(frameOffset, frameOffset + frameSize);

    return framePixelBuffer;
  } else {
    const frameFragmentsData = new Uint8Array(pixelBuffers[frame]);
    const pixel = pixelShim(
      dataset.Columns,
      dataset.Rows,
      dataset.BitsAllocated,
      dataset.BitsStored,
      dataset.SamplesPerPixel,
      dataset.PixelRepresentation,
      dataset.PlanarConfiguration,
      dataset.PhotometricInterpretation
    );

    if (transferSyntaxUid === '1.2.840.10008.1.2.5') {
      // RleLossless
      return dcmjsImaging.NativePixelDecoder.decodeRle(pixel, frameFragmentsData);
    } else if (
      // JpegBaselineProcess1, JpegBaselineProcess2_4
      transferSyntaxUid === '1.2.840.10008.1.2.4.50' ||
      transferSyntaxUid === '1.2.840.10008.1.2.4.51'
    ) {
      return dcmjsImaging.NativePixelDecoder.decodeJpeg(pixel, frameFragmentsData, {
        convertColorspaceToRgb: true,
      });
    } else if (
      // JpegLosslessProcess14, JpegLosslessProcess14V1
      transferSyntaxUid === '1.2.840.10008.1.2.4.57' ||
      transferSyntaxUid === '1.2.840.10008.1.2.4.70'
    ) {
      return dcmjsImaging.NativePixelDecoder.decodeJpeg(pixel, frameFragmentsData);
    } else if (
      // JpegLsLossless, JpegLsLossy
      transferSyntaxUid === '1.2.840.10008.1.2.4.80' ||
      transferSyntaxUid === '1.2.840.10008.1.2.4.81'
    ) {
      return dcmjsImaging.NativePixelDecoder.decodeJpegLs(pixel, frameFragmentsData);
    } else if (
      // Jpeg2000Lossless, Jpeg2000Lossy
      transferSyntaxUid === '1.2.840.10008.1.2.4.90' ||
      transferSyntaxUid === '1.2.840.10008.1.2.4.91'
    ) {
      return dcmjsImaging.NativePixelDecoder.decodeJpeg2000(pixel, frameFragmentsData);
    }

    throw new Error(`Transfer syntax cannot be currently decoded [${transferSyntaxUid}]`);
  }
};

module.exports = decodePixelData;