Объясните код, пожалуйста (png, rgba, пиксели)

def jpg_decryption(x, y):
    r, g, b = x
    r1, g1, b1 = y
    count = abs(r - r1) + abs(g - g1) * 2
    k = abs(b - b1)
    if k == 2:
        count += 64
    elif k == 1:
        count += 96
    elif k == 3:
        count += 45
    elif k == 4:
        count = 44
    elif k == 5:
        count = 32
    elif k == 6:
        count = 33
    elif k == 7:
        count = 63
    elif k == 8:
        count += 48
    elif k == 9:
        count = 10
    return count
 
 
def f(x, z):
    if x + z <= 255:
        z += x
    else:
        z -= x
    return z
 
 
def jpg(i, pixel, text):
    r, g, b = pixel
    s = ord(text[i])
    if 97 <= s <= 122:
        s -= 96
        b = f(1, b)
    elif 65 <= s <= 90:
        s -= 64
        b = f(2, b)
    elif 48 <= s <= 57:
        s -= 48
        b = f(8, b)
    elif s == 33:
        s = 1
        b = f(6, b)
    elif s == 63:
        s = 1
        b = f(7, b)
    elif s == 46:
        s = 1
        b = f(3, b)
    elif s == 44:
        s = 1
        b = f(4, b)
    elif s == 32:
        s = 1
        b = f(5, b)
    elif s == 10:
        s = 1
        b = f(9, b)
    x = s // 3
    z = s - x - x
    r = f(z, r)
    g = f(x, g)
    return r, g, b