private bool initYCbCrConversion()
{
if (ycbcr == null)
ycbcr = new TiffYCbCrToRGB();
FieldValue[] result = tif.GetFieldDefaulted(TiffTag.YCBCRCOEFFICIENTS);
float[] luma = result[0].ToFloatArray();
result = tif.GetFieldDefaulted(TiffTag.REFERENCEBLACKWHITE);
float[] refBlackWhite = result[0].ToFloatArray();
ycbcr.Init(luma, refBlackWhite);
return true;
}