code: public static <T extends ImageGray<T>> double variance(T input , double mean ) {
  
  		if( GrayU8.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayU8)input,mean);
  		} else if( GrayS8.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayS8)input,mean);
  		} else if( GrayU16.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayU16)input,mean);
  		} else if( GrayS16.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayS16)input,mean);
  		} else if( GrayS32.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayS32)input,mean);
  		} else if( GrayS64.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayS64)input,mean);
  		} else if( GrayF32.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayF32)input,(float)mean);
  		} else if( GrayF64.class == input.getClass() ) {
  			return ImageStatistics.variance((GrayF64)input,mean);
  		} else {
  			throw new IllegalArgumentException("Unknown image Type");
  		}
  	}
docs: Computes the variance of pixel intensity values inside the image.
  
  @param input Input image. Not modified.
  @param mean Mean pixel intensity value.
  @return Pixel variance