public static strictfp int getBrightness(int rgb){
        int r = (rgb & 0xFF0000) >> 16;
        int g = (rgb & 0xFF00) >> 8;
        int b = (rgb & 0xFF);
        int brightness = (int)(r * 0.299 + g * 0.587 + b * 0.114);
        assert brightness>=0 && brightness<256;
        return brightness;
    }

    // TODO: remove global
    static int statisticAmax = 0;

    public static strictfp double esimateNrmsRatioInBrightnessChannel(BufferedImage ethalon,BufferedImage noised){
        int ex = ethalon.getWidth();
        int ey = ethalon.getHeight();
        int nx = ethalon.getWidth();
        int ny = ethalon.getHeight();
        if (ex!=nx || ey!=ny) throw new IllegalArgumentException("Ethalon image and noised shoild be equals");
        int k = ex * ey;
        double nrms = 0.0;
        int amax = 0;
        for(int y = 0; y < ey ; y++){
            for(int x = 0; x < ex ; x++){
                int eb = getBrightness(ethalon.getRGB(x, y));
                int nb = getBrightness(noised.getRGB(x, y));
                int delta = abs(eb - nb);
                amax = max(amax,delta);
                nrms+=(double)(delta*delta);
            }
        }
        statisticAmax = amax;
        return sqrt(nrms / k);
    }
....
...
        BufferedImage ethalonImage = ImageIO.read(new FileInputStream(ethalon));

        BufferedImage noisedImage = ImageIO.read(new FileInputStream(noised));

        long begin = System.currentTimeMillis();
        double nrms = esimateNrmsRatioInBrightnessChannel(ethalonImage, noisedImage);
        long end = System.currentTimeMillis();

        printf("Image size                              : %d x %d\n",ethalonImage.getWidth(),ethalonImage.getHeight());
        printf("Elapsed time                            : %d s\n",(end-begin)/1000);
        printf("Nrms (standard deviation)               : %f\n",nrms);
        printf("Psnr (peak-to-peak signal-to-noise ratio: %f\n",20*log10(statisticAmax/nrms));