PCA Color Augmentation

pca_aug.py

import numpy as np

# original image is 224x224x3 of dtype uint8 


renorm_image = np.reshape(original_image, (original_image.shape[0]*original_image.shape[1],3))

renorm_image = renorm_image.astype('float32')
renorm_image -= np.mean(renorm_image, axis=0)
renorm_image /= np.std(renorm_image, axis=0)

cov = np.cov(renorm_image, rowvar=False)

lambdas, p = np.linalg.eig(cov)
alphas = np.random.normal(0, 0.1, 3)

#delta = p[:,0]*alphas[0]*lambdas[0] + p[:,1]*alphas[1]*lambdas[1] + p[:,2]*alphas[2]*lambdas[2]
delta = np.dot(p, alphas*lambdas)

delta = (delta*255.).astype('int8')

pca_color_image = np.maximum(np.minimum(original_image + delta, 255), 0).astype('uint8')