code: private void CheckTransparencyMask(IfdTags metadata, int n) {
      // Samples per pixel
      if (!metadata.containsTagId(TiffTags.getTagId("SamplesPerPixel"))) {
        validation.addErrorLoc("Missing Samples Per Pixel", "IFD" + n);
      } else {
        long spp = metadata.get(TiffTags.getTagId("SamplesPerPixel")).getFirstNumericValue();
        if (spp != 1) {
          validation.addError("Invalid Samples Per Pixel", "IFD" + n, spp);
        }
      }
  
      // BitsPerSample
      if (!metadata.containsTagId(TiffTags.getTagId("BitsPerSample"))) {
        validation.addErrorLoc("Missing BitsPerSample", "IFD" + n);
      } else {
        long bps = metadata.get(TiffTags.getTagId("BitsPerSample")).getFirstNumericValue();
        if (bps != 1) {
          validation.addError("Invalid BitsPerSample", "IFD" + n, bps);
        }
      }
    }
docs: Check transparency mask.
  
  @param metadata the metadata
  @param n the ifd number