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utils: raspberrypi: ctt: Improved color matrix fitting

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Added code which optimises the color matrices based off
delta E values for the calibration images. Working in LAB
color space.

Signed-off-by: Ben Benson <ben.benson@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
This commit is contained in:
Ben Benson 2023-07-07 04:17:00 +01:00 • committed by Naushir Patuck
parent a2eadc40a7
commit f8dd17a8f4
3 changed files with 300 additions and 38 deletions
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30
utils/raspberrypi/ctt/colors.py Normal file
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# colors.py - Program to convert from RGB to LAB color space
def RGB_to_LAB(RGB): # where RGB is a 1x3 array. e.g RGB = [100, 255, 230]
num = 0
XYZ = [0, 0, 0]
# converted all the three R, G, B to X, Y, Z
X = RGB[0] * 0.4124 + RGB[1] * 0.3576 + RGB[2] * 0.1805
Y = RGB[0] * 0.2126 + RGB[1] * 0.7152 + RGB[2] * 0.0722
Z = RGB[0] * 0.0193 + RGB[1] * 0.1192 + RGB[2] * 0.9505
XYZ[0] = X / 255 * 100
XYZ[1] = Y / 255 * 100 # XYZ Must be in range 0 -> 100, so scale down from 255
XYZ[2] = Z / 255 * 100
XYZ[0] = XYZ[0] / 95.047 # ref_X = 95.047 Observer= 2°, Illuminant= D65
XYZ[1] = XYZ[1] / 100.0 # ref_Y = 100.000
XYZ[2] = XYZ[2] / 108.883 # ref_Z = 108.883
num = 0
for value in XYZ:
if value > 0.008856:
value = value ** (0.3333333333333333)
else:
value = (7.787 * value) + (16 / 116)
XYZ[num] = value
num = num + 1
# L, A, B, values calculated below
L = (116 * XYZ[1]) - 16
a = 500 * (XYZ[0] - XYZ[1])
b = 200 * (XYZ[1] - XYZ[2])
return [L, a, b]

221
utils/raspberrypi/ctt/ctt_ccm.py
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@ -6,27 +6,66 @@
from ctt_image_load import *
from ctt_awb import get_alsc_patches
import colors
from scipy.optimize import minimize
from ctt_visualise import visualise_macbeth_chart
import numpy as np
"""
takes 8-bit macbeth chart values, degammas and returns 16 bit
"""
'''
This program has many options from which to derive the color matrix from.
The first is average. This minimises the average delta E across all patches of
the macbeth chart. Testing across all cameras yeilded this as the most color
accurate and vivid. Other options are avalible however.
Maximum minimises the maximum Delta E of the patches. It iterates through till
a minimum maximum is found (so that there is
not one patch that deviates wildly.)
This yields generally good results but overall the colors are less accurate
Have a fiddle with maximum and see what you think.
The final option allows you to select the patches for which to average across.
This means that you can bias certain patches, for instance if you want the
reds to be more accurate.
'''
matrix_selection_types = ["average", "maximum", "patches"]
typenum = 0 # select from array above, 0 = average, 1 = maximum, 2 = patches
test_patches = [1, 2, 5, 8, 9, 12, 14]
'''
Enter patches to test for. Can also be entered twice if you
would like twice as much bias on one patch.
'''
def degamma(x):
x = x / ((2**8)-1)
x = x / ((2 ** 8) - 1) # takes 255 and scales it down to one
x = np.where(x < 0.04045, x / 12.92, ((x + 0.055) / 1.055) ** 2.4)
x = x * ((2**16)-1)
x = x * ((2 ** 16) - 1) # takes one and scales up to 65535, 16 bit color
return x
def gamma(x):
# return (x * * (1 / 2.4) * 1.055 - 0.055)
e = []
for i in range(len(x)):
e.append(((x[i] / 255) ** (1 / 2.4) * 1.055 - 0.055) * 255)
return e
"""
FInds colour correction matrices for list of images
"""
def ccm(Cam, cal_cr_list, cal_cb_list):
global matrix_selection_types, typenum
imgs = Cam.imgs
"""
standard macbeth chart colour values
"""
m_rgb = np.array([ # these are in sRGB
m_rgb = np.array([ # these are in RGB
[116, 81, 67], # dark skin
[199, 147, 129], # light skin
[91, 122, 156], # blue sky
@ -52,16 +91,22 @@ def ccm(Cam, cal_cr_list, cal_cb_list):
[82, 84, 86], # neutral 3.5
[49, 49, 51] # black 2
])
"""
convert reference colours from srgb to rgb
"""
m_srgb = degamma(m_rgb)
m_srgb = degamma(m_rgb) # now in 16 bit color.
m_lab = []
for col in m_srgb:
m_lab.append(colors.RGB_to_LAB(col / 256))
# This produces matrix of LAB values for ideal color chart)
"""
reorder reference values to match how patches are ordered
"""
m_srgb = np.array([m_srgb[i::6] for i in range(6)]).reshape((24, 3))
m_lab = np.array([m_lab[i::6] for i in range(6)]).reshape((24, 3))
m_rgb = np.array([m_rgb[i::6] for i in range(6)]).reshape((24, 3))
"""
reformat alsc correction tables or set colour_cals to None if alsc is
deactivated
@ -94,6 +139,8 @@ def ccm(Cam, cal_cr_list, cal_cb_list):
the function will simply return the macbeth patches
"""
r, b, g = get_alsc_patches(Img, colour_cals, grey=False)
# 256 values for each patch of sRGB values
"""
do awb
Note: awb is done by measuring the macbeth chart in the image, rather
@ -105,7 +152,6 @@ def ccm(Cam, cal_cr_list, cal_cb_list):
b_g = np.mean(b_greys / g_greys)
r = r / r_g
b = b / b_g
"""
normalise brightness wrt reference macbeth colours and then average
each channel for each patch
@ -115,20 +161,110 @@ def ccm(Cam, cal_cr_list, cal_cb_list):
r = np.mean(gain * r, axis=1)
b = np.mean(gain * b, axis=1)
g = np.mean(gain * g, axis=1)
"""
calculate ccm matrix
"""
# ==== All of below should in sRGB ===##
sumde = 0
ccm = do_ccm(r, g, b, m_srgb)
# This is the initial guess that our optimisation code works with.
r1 = ccm[0]
r2 = ccm[1]
g1 = ccm[3]
g2 = ccm[4]
b1 = ccm[6]
b2 = ccm[7]
'''
COLOR MATRIX LOOKS AS BELOW
R1 R2 R3 Rval Outr
G1 G2 G3 * Gval = G
B1 B2 B3 Bval B
Will be optimising 6 elements and working out the third element using 1-r1-r2 = r3
'''
x0 = [r1, r2, g1, g2, b1, b2]
'''
We use our old CCM as the initial guess for the program to find the
optimised matrix
'''
result = minimize(guess, x0, args=(r, g, b, m_lab), tol=0.0000000001)
'''
This produces a color matrix which has the lowest delta E possible,
based off the input data. Note it is impossible for this to reach
zero since the input data is imperfect
'''
Cam.log += ("\n \n Optimised Matrix Below: \n \n")
[r1, r2, g1, g2, b1, b2] = result.x
# The new, optimised color correction matrix values
optimised_ccm = [r1, r2, (1 - r1 - r2), g1, g2, (1 - g1 - g2), b1, b2, (1 - b1 - b2)]
# This is the optimised Color Matrix (preserving greys by summing rows up to 1)
Cam.log += str(optimised_ccm)
Cam.log += "\n Old Color Correction Matrix Below \n"
Cam.log += str(ccm)
formatted_ccm = np.array(ccm).reshape((3, 3))
'''
below is a whole load of code that then applies the latest color
matrix, and returns LAB values for color. This can then be used
to calculate the final delta E
'''
optimised_ccm_rgb = [] # Original Color Corrected Matrix RGB / LAB
optimised_ccm_lab = []
for w in range(24):
RGB = np.array([r[w], g[w], b[w]])
ccm_applied_rgb = np.dot(formatted_ccm, (RGB / 256))
optimised_ccm_rgb.append(gamma(ccm_applied_rgb))
optimised_ccm_lab.append(colors.RGB_to_LAB(ccm_applied_rgb))
formatted_optimised_ccm = np.array(ccm).reshape((3, 3))
after_gamma_rgb = []
after_gamma_lab = []
for w in range(24):
RGB = np.array([r[w], g[w], b[w]])
optimised_ccm_applied_rgb = np.dot(formatted_optimised_ccm, RGB / 256)
after_gamma_rgb.append(gamma(optimised_ccm_applied_rgb))
after_gamma_lab.append(colors.RGB_to_LAB(optimised_ccm_applied_rgb))
'''
Gamma After RGB / LAB
We now want to spit out some data that shows
how the optimisation has improved the color matrices
'''
Cam.log += "Here are the Improvements"
# CALCULATE WORST CASE delta e
old_worst_delta_e = 0
before_average = transform_and_evaluate(formatted_ccm, r, g, b, m_lab)
new_worst_delta_e = 0
after_average = transform_and_evaluate(formatted_optimised_ccm, r, g, b, m_lab)
for i in range(24):
old_delta_e = deltae(optimised_ccm_lab[i], m_lab[i]) # Current Old Delta E
new_delta_e = deltae(after_gamma_lab[i], m_lab[i]) # Current New Delta E
if old_delta_e > old_worst_delta_e:
old_worst_delta_e = old_delta_e
if new_delta_e > new_worst_delta_e:
new_worst_delta_e = new_delta_e
Cam.log += "Before color correction matrix was optimised, we got an average delta E of " + str(before_average) + " and a maximum delta E of " + str(old_worst_delta_e)
Cam.log += "After color correction matrix was optimised, we got an average delta E of " + str(after_average) + " and a maximum delta E of " + str(new_worst_delta_e)
visualise_macbeth_chart(m_rgb, optimised_ccm_rgb, after_gamma_rgb, str(Img.col) + str(matrix_selection_types[typenum]))
'''
The program will also save some visualisations of improvements.
Very pretty to look at. Top rectangle is ideal, Left square is
before optimisation, right square is after.
'''
"""
if a ccm has already been calculated for that temperature then don't
overwrite but save both. They will then be averaged later on
"""
""" # Now going to use optimised color matrix, optimised_ccm
if Img.col in ccm_tab.keys():
ccm_tab[Img.col].append(ccm)
ccm_tab[Img.col].append(optimised_ccm)
else:
ccm_tab[Img.col] = [ccm]
ccm_tab[Img.col] = [optimised_ccm]
Cam.log += '\n'
Cam.log += '\nFinished processing images'
@ -156,14 +292,61 @@ def ccm(Cam, cal_cr_list, cal_cb_list):
return ccms
def guess(x0, r, g, b, m_lab): # provides a method of numerical feedback for the optimisation code
[r1, r2, g1, g2, b1, b2] = x0
ccm = np.array([r1, r2, (1 - r1 - r2),
g1, g2, (1 - g1 - g2),
b1, b2, (1 - b1 - b2)]).reshape((3, 3)) # format the matrix correctly
return transform_and_evaluate(ccm, r, g, b, m_lab)
def transform_and_evaluate(ccm, r, g, b, m_lab): # Transforms colors to LAB and applies the correction matrix
# create list of matrix changed colors
realrgb = []
for i in range(len(r)):
RGB = np.array([r[i], g[i], b[i]])
rgb_post_ccm = np.dot(ccm, RGB) # This is RGB values after the color correction matrix has been applied
realrgb.append(colors.RGB_to_LAB(rgb_post_ccm))
# now compare that with m_lab and return numeric result, averaged for each patch
return (sumde(realrgb, m_lab) / 24) # returns an average result of delta E
def sumde(listA, listB):
global typenum, test_patches
sumde = 0
maxde = 0
patchde = []
for i in range(len(listA)):
if maxde < (deltae(listA[i], listB[i])):
maxde = deltae(listA[i], listB[i])
patchde.append(deltae(listA[i], listB[i]))
sumde += deltae(listA[i], listB[i])
'''
The different options specified at the start allow for
the maximum to be returned, average or specific patches
'''
if typenum == 0:
return sumde
if typenum == 1:
return maxde
if typenum == 2:
output = 0
for y in range(len(test_patches)):
output += patchde[test_patches[y]] # grabs the specific patches (no need for averaging here)
return output
"""
calculates the ccm for an individual image.
ccms are calculate in rgb space, and are fit by hand. Although it is a 3x3
ccms are calculated in rgb space, and are fit by hand. Although it is a 3x3
matrix, each row must add up to 1 in order to conserve greyness, simplifying
calculation.
Should you want to fit them in another space (e.g. LAB) we wish you the best of
luck and send us the code when you are done! :-)
The initial CCM is calculated in RGB, and then optimised in LAB color space
This simplifies the initial calculation but then gets us the accuracy of
using LAB color space.
"""
def do_ccm(r, g, b, m_srgb):
rb = r-b
gb = g-b
@ -222,3 +405,9 @@ def do_ccm(r, g, b, m_srgb):
ccm = [r_a, r_b, r_c, g_a, g_b, g_c, b_a, b_b, b_c]
return ccm
def deltae(colorA, colorB):
return ((colorA[0] - colorB[0]) ** 2 + (colorA[1] - colorB[1]) ** 2 + (colorA[2] - colorB[2]) ** 2) ** 0.5
# return ((colorA[1]-colorB[1]) * * 2 + (colorA[2]-colorB[2]) * * 2) * * 0.5
# UNCOMMENT IF YOU WANT TO NEGLECT LUMINANCE FROM CALCULATION OF DELTA E

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utils/raspberrypi/ctt/ctt_visualise.py Normal file
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"""
Some code that will save virtual macbeth charts that show the difference between optimised matrices and non optimised matrices
The function creates an image that is 1550 by 1050 pixels wide, and fills it with patches which are 200x200 pixels in size
Each patch contains the ideal color, the color from the original matrix, and the color from the final matrix
_________________
| |
| Ideal Color |
|_______________|
| Old | new |
| Color | Color |
|_______|_______|
Nice way of showing how the optimisation helps change the colors and the color matricies
"""
import numpy as np
from PIL import Image
def visualise_macbeth_chart(macbeth_rgb, original_rgb, new_rgb, output_filename):
image = np.zeros((1050, 1550, 3), dtype=np.uint8)
colorindex = -1
for y in range(6):
for x in range(4): # Creates 6 x 4 grid of macbeth chart
colorindex += 1
xlocation = 50 + 250 * x # Means there is 50px of black gap between each square, more like the real macbeth chart.
ylocation = 50 + 250 * y
for g in range(200):
for i in range(100):
image[xlocation + i, ylocation + g] = macbeth_rgb[colorindex]
xlocation = 150 + 250 * x
ylocation = 50 + 250 * y
for i in range(100):
for g in range(100):
image[xlocation + i, ylocation + g] = original_rgb[colorindex] # Smaller squares below to compare the old colors with the new ones
xlocation = 150 + 250 * x
ylocation = 150 + 250 * y
for i in range(100):
for g in range(100):
image[xlocation + i, ylocation + g] = new_rgb[colorindex]
img = Image.fromarray(image, 'RGB')
img.save(str(output_filename) + 'Generated Macbeth Chart.png')