gamma校正

gamma校正可使得图像看起来更符合人眼的特性。gamma校正公式常写为Out= In^gamma或者Out= In^1/gamma形式，式中，In表示Input image, Out 表示Output image。本文采用第一种形式。gamma校正前后图像的亮度对比如下图所示。本文分别用opencv-python和MATLAB实现了gamma校正。

1. opencv-python实现gamma校正

import cv2
import numpy as np
import matplotlib.pyplot as plt

gamma1 = 0.4
gamma2 = 2.5

imgIn = cv2.imread('messi.jpg', 0)
imgIn = imgIn.astype(float) / 255

out1 = imgIn ** gamma1
out2 = imgIn ** gamma2

out1 *= 255
out1[out1 < 0] = 0
out1[out1 > 255] = 255
out1 = out1.astype(np.uint8)

out2 *= 255
out2[out2 < 0] = 0
out2[out2 > 255] = 255
out2 = out2.astype(np.uint8)

# show images
plt.subplot(131)
plt.title('gamma=0.4')
plt.xticks([])  # 去除刻度
plt.yticks([])
plt.imshow(out1, cmap='gray')

plt.subplot(132)
plt.title('original image')
plt.xticks([])
plt.yticks([])
plt.imshow(imgIn, cmap='gray')

plt.subplot(133)
plt.title('gamma=2.5')
plt.xticks([])
plt.yticks([])
plt.imshow(out2, cmap='gray')
plt.show()

效果如下：

 2. MATLAB实现gamma校正

clear;
img_ori = imread('Fig0308(a)(fractured_spine).tif');

img_mat = mat2gray(img_ori, [0 255]);

c = 1;
gamma03 = 0.3;
gamma06 = 0.6;
gamma25 = 2.5;

img_gam03 = c*(img_mat.^gamma03);
img_gam06 = c*(img_mat.^gamma06);
img_gam25 = c*(img_mat.^gamma25);

% show images
figure;
subplot(1,4,1);
imshow(img_mat, [0, 1]);
title('original image');

subplot(1,4,2);
imshow(img_gam03, [0, 1]);
title('gamma=0.3');

subplot(1,4,3);
imshow(img_gam06, [0, 1]);
title('gamma=0.6');

subplot(1,4,4);
imshow(img_gam25, [0, 1]);
title('gamma=2.5');

效果如下：