import cv2 as cv
import numpy as np

#Y = 0.299*R + 0.587*G + 0.114*B
#Cb = 128 + 0.5*B + -0.331264*G + -0.168736*R
#Cr = 128 + -0.081312*B + -0.418688*G + 0.5*R
def BGR2YCbCr(bgrimg):
    ycbcrimg = np.empty(bgrimg.shape,dtype=np.float)
    for r in range(bgrimg.shape[0]):
        for c in range(bgrimg.shape[1]):
            #y = 0.299*bgrimg[r,c,2] + 0.587*bgrimg[r,c,1] + 0.114*bgrimg[r,c,0]
            y = sum(bgrimg[r,c]*np.array([0.114, 0.587, 0.299]))
            cb = 128 + sum(bgrimg[r,c]*np.array([0.5, -0.331264, -0.168736]))
            cr = 128 + sum(bgrimg[r,c]*np.array([-0.081312, -0.418688, 0.5]))
            ycbcrimg[r,c] = np.array([y,cb,cr])
    
    return ycbcrimg

#R = Y + 1.402 * (Cr - 128)
#G = Y - 0.344136 * (Cb - 128) + -0.714136 * (Cr - 128)
#B = Y + 1.772 * (Cb - 128)
def YCbCr2BGR(ycbcrimg):
    bgrimg = np.empty(ycbcrimg.shape,dtype=np.uint8)
    for r in range(ycbcrimg.shape[0]):
        for c in range(ycbcrimg.shape[1]):
            red = int(ycbcrimg[r,c,0] + 1.402 * (ycbcrimg[r,c,2] - 128))
            if red < 0:
                red = 0
            else:
                if red > 255:
                    red = 255
            green = int(ycbcrimg[r,c,0] - 0.344136 * (ycbcrimg[r,c,1] - 128)) + -0.714136 * (ycbcrimg[r,c,2] - 128)
            if green < 0:
                green = 0
            else:
                if green > 255:
                    green = 255
            blue = int(ycbcrimg[r,c,0] + 1.772 * (ycbcrimg[r,c,1] - 128))
            if blue < 0:
                blue = 0
            else:
                if blue > 255:
                    blue = 255
            bgrimg[r,c] = np.array([blue, green, red])
    return bgrimg



inimg = cv.imread('bball.jpg')

cv.imshow('Input image', inimg)
k = cv.waitKey(0)
cv.destroyAllWindows()

ycbcrinimg = BGR2YCbCr(inimg)

gaussian13sd5 = cv.getGaussianKernel(13, 5)
gaussianmask = gaussian13sd5.transpose() * gaussian13sd5

grayblur = cv.filter2D(ycbcrinimg[:,:,0], -1, gaussianmask)

ycbcrinimg[:,:,0] = grayblur

bgroutimg = YCbCr2BGR(ycbcrinimg)

cv.imshow('Original', inimg)
cv.imshow('blurred (first converted to YCbCr, then blurred Y)', bgroutimg)
cv.waitKey(0)
cv.destroyAllWindows()

cv.imwrite('blurredimg.jpg', bgroutimg)