grib/src/main/java/ucar/nc2/grib/grib2/Grib2DataReader.java
private float[] getData41(RandomAccessFile raf, Grib2Drs.Type0 gdrs) throws IOException {
    int nb = gdrs.numberOfBits;
    int D = gdrs.decimalScaleFactor;
    float DD = (float) java.lang.Math.pow((double) 10, (double) D);
    float R = gdrs.referenceValue;
    int E = gdrs.binaryScaleFactor;
    float EE = (float) java.lang.Math.pow(2.0, (double) E);

    // LOOK: can # datapoints differ from bitmap and data ?
    // dataPoints are number of points encoded, it could be less than the
    // totalNPoints in the grid record if bitMap is used, otherwise equal
    float[] data = new float[totalNPoints];

    // no data to decode, set to reference value
    if (nb == 0) {
      Arrays.fill(data, R);
      return data;
    }

    //  Y * 10**D = R + (X1 + X2) * 2**E
    //   E = binary scale factor
    //   D = decimal scale factor
    //   R = reference value
    //   X1 = 0
    //   X2 = scaled encoded value
    //   data[ i ] = (R + ( X1 + X2) * EE)/DD ;

    byte[] buf = new byte[dataLength - 5];
    raf.readFully(buf);
    InputStream in = new ByteArrayInputStream(buf);
    BufferedImage image = ImageIO.read(in);

    if (nb != image.getColorModel().getPixelSize()) {
      logger.debug("PNG pixel size disagrees with grib number of bits: ",
          image.getColorModel().getPixelSize(), nb);
    }

    DataBuffer db = image.getRaster().getDataBuffer();
    if (bitmap == null) {
      for (int i = 0; i < dataNPoints; i++) {
        data[i] = (R + db.getElem(i) * EE) / DD;
      }
    } else {
      for (int bitPt = 0, dataPt = 0; bitPt < totalNPoints; bitPt++) {
        if (GribNumbers.testBitIsSet(bitmap[bitPt / 8], bitPt % 8)) {
          data[bitPt] = (R + db.getElem(dataPt++) * EE) / DD;
        } else {
          data[bitPt] = staticMissingValue;
        }
      }
    }

    return data;
  }
private float[] getData41(RandomAccessFile raf, Grib2Drs.Type0 gdrs) throws IOException {
    int nb = gdrs.numberOfBits;
    int D = gdrs.decimalScaleFactor;
    float DD = (float) java.lang.Math.pow((double) 10, (double) D);
    float R = gdrs.referenceValue;
    int E = gdrs.binaryScaleFactor;
    float EE = (float) java.lang.Math.pow(2.0, (double) E);

    // LOOK: can # datapoints differ from bitmap and data ?
    // dataPoints are number of points encoded, it could be less than the
    // totalNPoints in the grid record if bitMap is used, otherwise equal
    float[] data = new float[totalNPoints];

    // no data to decode, set to reference value
    if (nb == 0) {
      Arrays.fill(data, R);
      return data;
    }

    //  Y * 10**D = R + (X1 + X2) * 2**E
    //   E = binary scale factor
    //   D = decimal scale factor
    //   R = reference value
    //   X1 = 0
    //   X2 = scaled encoded value
    //   data[ i ] = (R + ( X1 + X2) * EE)/DD ;

    byte[] buf = new byte[dataLength - 5];
    raf.readFully(buf);
    InputStream in = new ByteArrayInputStream(buf);
    BufferedImage image = ImageIO.read(in);

    if (nb != image.getColorModel().getPixelSize()) {
      logger.debug("PNG pixel size disagrees with grib number of bits: ",
          image.getColorModel().getPixelSize(), nb);
    }

    DataBuffer db = image.getRaster().getDataBuffer();
    if (bitmap == null) {
      for (int i = 0; i < dataNPoints; i++) {
        data[i] = (R + db.getElem(i) * EE) / DD;
      }
    } else {
      for (int bitPt = 0, dataPt = 0; bitPt < totalNPoints; bitPt++) {
        if (GribNumbers.testBitIsSet(bitmap[bitPt / 8], bitPt % 8)) {
          data[bitPt] = (R + db.getElem(dataPt++) * EE) / DD;
        } else {
          data[bitPt] = staticMissingValue;
        }
      }
    }

    return data;
  }
Code taken from esupport ticket ZVT-415274