In [1]:
%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
import scipy.signal
import scipy.interpolate
import scipy.stats
In [2]:
original = plt.imread('2.tiff')
plt.figure(figsize = (14,14), facecolor = 'w')
plt.imshow(original)
plt.title('Calibration image (taken with a photo camera)');
The format of raw images is little-endian 16 bit integers. Only the 10 least-significant bits are used in N2.raw, while only the 12 least-significant bits are used in N3.raw.
In [3]:
data_10bits = np.fromfile('N2.raw', dtype = 'int16')
plt.hist(data_10bits, bins = 100)
plt.title('10 bit raw image histogram');
In [4]:
data_12bits = np.fromfile('N3.raw', dtype = 'int16')
plt.hist(data_12bits, bins = 100)
plt.title('12 bit raw image histogram');
The functions below extract the Red, Green, Blue and White pixels, perform interpolation on each channel to the full image resolution, convert RGB values to CbCr, take the White values as Y' and convert Y'CbCr back to RGB.
In [5]:
def get_channel(img, a_off, b_off):
step = 8
img_chan = img[a_off::8, b_off::8]
f = scipy.interpolate.interp2d(np.arange(a_off,img.shape[1],8), np.arange(b_off,img.shape[0],8), img_chan,
kind = 'cubic')
return f(np.arange(img.shape[1]), np.arange(img.shape[0]))
def get_green_channel(img):
img_G1 = img[4::8, ::8]
img_G2 = img[::8, 4::8]
points1 = np.mgrid[4:img.shape[0]:8, :img.shape[1]:8].reshape((2,-1)).transpose()
points2 = np.mgrid[:img.shape[0]:8, 4:img.shape[1]:8].reshape((2,-1)).transpose()
points = np.concatenate((points1, points2))
img_G = np.concatenate((img_G1.ravel(), img_G2.ravel()))
a, b = np.mgrid[:img.shape[0], :img.shape[1]]
return scipy.interpolate.griddata(points, img_G, (a, b), method = 'cubic')
def get_luminance_channel(img):
img_Y1 = img[1::4, :]
img_Y2 = img[2::4, :]
img_Y3 = img[3::4, :]
img_Y4 = img[:, 1::4]
img_Y5 = img[:, 2::4]
img_Y6 = img[:, 3::4]
points1 = np.mgrid[1:img.shape[0]:4, :img.shape[1]].reshape((2,-1)).transpose()
points2 = np.mgrid[2:img.shape[0]:4, :img.shape[1]].reshape((2,-1)).transpose()
points3 = np.mgrid[3:img.shape[0]:4, :img.shape[1]].reshape((2,-1)).transpose()
points4 = np.mgrid[:img.shape[0], 1:img.shape[1]:4].reshape((2,-1)).transpose()
points5 = np.mgrid[:img.shape[0], 2:img.shape[1]:4].reshape((2,-1)).transpose()
points6 = np.mgrid[:img.shape[0], 3:img.shape[1]:4].reshape((2,-1)).transpose()
points = np.concatenate((points1, points2, points3, points4, points5, points6))
img_Y = np.concatenate((img_Y1.ravel(), img_Y2.ravel(), img_Y3.ravel(), img_Y4.ravel(),
img_Y5.ravel(), img_Y6.ravel()))
a, b = np.mgrid[:img.shape[0], :img.shape[1]]
return scipy.interpolate.griddata(points, img_Y, (a, b), method = 'nearest')
def get_RGB(data, nbits, ncols = 1280):
data = np.clip(data, 0, 2**nbits-1)
img = data[:data.size//ncols*ncols].reshape((-1,ncols)).astype('float')
# scale to [0,256)
img *= 2**(8-nbits)
# The sensor colour filter array is
# *-----------------*
# | B W W W G W W W |
# | W W W W W W W W |
# | W W W W W W W W |
# | G W W W R W W W |
# | W W W W W W W W |
# | W W W W W W W W |
# *-----------------*
img_B = get_channel(img, 0, 0)
img_R = get_channel(img, 4, 4)
img_G = get_green_channel(img)
img_Y = get_luminance_channel(img)
# JPEG Y'CbCr conversion
img_Cb = -0.168736*img_R-0.331264*img_G+0.5*img_B+128
img_Cr = 0.5*img_R-0.418688*img_G-0.081312*img_B+128
# CbCr translation for white calibration (determined experimentally with calibration image)
Cb_translation = 14.47
Cr_translation = -20.96
img_Cb += Cb_translation
img_Cr += Cr_translation
img_R2 = img_Y + 1.402*(img_Cr-128)
img_G2 = img_Y - 0.344136*(img_Cb-128) - 0.714136*(img_Cr-128)
img_B2 = img_Y + 1.772*(img_Cb-128)
img_RGB = np.stack((img_R2, img_G2, img_B2), axis = -1)
return np.clip(np.round(img_RGB), 0, 255).astype('uint8'), img_Y, img_Cb, img_Cr
In [6]:
img_RGB_12bits = get_RGB(data_12bits, 12)[0]
img_RGB_10bits = get_RGB(data_10bits, 10)[0]
In [7]:
plt.figure(figsize = (14,14))
plt.imshow(img_RGB_12bits)
plt.title('Render of 12 bit raw image')
plt.figure(figsize = (14,14))
plt.imshow(img_RGB_10bits)
plt.title('Render of 10 bit raw image');