code: public static List<double[]> coupledRGB( List<File> images ) {
  		List<double[]> points = new ArrayList<>();
  
  		Planar<GrayF32> rgb = new Planar<>(GrayF32.class,1,1,3);
  
  		for( File f : images ) {
  			BufferedImage buffered = UtilImageIO.loadImage(f.getPath());
  			if( buffered == null ) throw new RuntimeException("Can't load image!");
  
  			rgb.reshape(buffered.getWidth(), buffered.getHeight());
  			ConvertBufferedImage.convertFrom(buffered, rgb, true);
  
  			// The number of bins is an important parameter.  Try adjusting it
  			Histogram_F64 histogram = new Histogram_F64(10,10,10);
  			histogram.setRange(0, 0, 255);
  			histogram.setRange(1, 0, 255);
  			histogram.setRange(2, 0, 255);
  
  			GHistogramFeatureOps.histogram(rgb,histogram);
  
  			UtilFeature.normalizeL2(histogram); // normalize so that image size doesn't matter
  
  			points.add(histogram.value);
  		}
  
  		return points;
  	}
docs: Constructs a 3D histogram using RGB.  RGB is a popular color space, but the resulting histogram will
  depend on lighting conditions and might not produce the accurate results.