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import cv2
import math
import numpy as np
import os
from scipy.ndimage import convolve
from scipy.special import gamma
from basicsr.metrics.metric_util import reorder_image, to_y_channel
from basicsr.utils.matlab_functions import imresize
from basicsr.utils.registry import METRIC_REGISTRY
def estimate_aggd_param(block):
"""Estimate AGGD (Asymmetric Generalized Gaussian Distribution) parameters.
Args:
block (ndarray): 2D Image block.
Returns:
tuple: alpha (float), beta_l (float) and beta_r (float) for the AGGD
distribution (Estimating the parames in Equation 7 in the paper).
"""
block = block.flatten()
gam = np.arange(0.2, 10.001, 0.001) # len = 9801
gam_reciprocal = np.reciprocal(gam)
r_gam = np.square(gamma(gam_reciprocal * 2)) / (gamma(gam_reciprocal) * gamma(gam_reciprocal * 3))
left_std = np.sqrt(np.mean(block[block < 0]**2))
right_std = np.sqrt(np.mean(block[block > 0]**2))
gammahat = left_std / right_std
rhat = (np.mean(np.abs(block)))**2 / np.mean(block**2)
rhatnorm = (rhat * (gammahat**3 + 1) * (gammahat + 1)) / ((gammahat**2 + 1)**2)
array_position = np.argmin((r_gam - rhatnorm)**2)
alpha = gam[array_position]
beta_l = left_std * np.sqrt(gamma(1 / alpha) / gamma(3 / alpha))
beta_r = right_std * np.sqrt(gamma(1 / alpha) / gamma(3 / alpha))
return (alpha, beta_l, beta_r)
def compute_feature(block):
"""Compute features.
Args:
block (ndarray): 2D Image block.
Returns:
list: Features with length of 18.
"""
feat = []
alpha, beta_l, beta_r = estimate_aggd_param(block)
feat.extend([alpha, (beta_l + beta_r) / 2])
# distortions disturb the fairly regular structure of natural images.
# This deviation can be captured by analyzing the sample distribution of
# the products of pairs of adjacent coefficients computed along
# horizontal, vertical and diagonal orientations.
shifts = [[0, 1], [1, 0], [1, 1], [1, -1]]
for i in range(len(shifts)):
shifted_block = np.roll(block, shifts[i], axis=(0, 1))
alpha, beta_l, beta_r = estimate_aggd_param(block * shifted_block)
# Eq. 8
mean = (beta_r - beta_l) * (gamma(2 / alpha) / gamma(1 / alpha))
feat.extend([alpha, mean, beta_l, beta_r])
return feat
def niqe(img, mu_pris_param, cov_pris_param, gaussian_window, block_size_h=96, block_size_w=96):
"""Calculate NIQE (Natural Image Quality Evaluator) metric.
``Paper: Making a "Completely Blind" Image Quality Analyzer``
This implementation could produce almost the same results as the official
MATLAB codes: http://live.ece.utexas.edu/research/quality/niqe_release.zip
Note that we do not include block overlap height and width, since they are
always 0 in the official implementation.
For good performance, it is advisable by the official implementation to
divide the distorted image in to the same size patched as used for the
construction of multivariate Gaussian model.
Args:
img (ndarray): Input image whose quality needs to be computed. The
image must be a gray or Y (of YCbCr) image with shape (h, w).
Range [0, 255] with float type.
mu_pris_param (ndarray): Mean of a pre-defined multivariate Gaussian
model calculated on the pristine dataset.
cov_pris_param (ndarray): Covariance of a pre-defined multivariate
Gaussian model calculated on the pristine dataset.
gaussian_window (ndarray): A 7x7 Gaussian window used for smoothing the
image.
block_size_h (int): Height of the blocks in to which image is divided.
Default: 96 (the official recommended value).
block_size_w (int): Width of the blocks in to which image is divided.
Default: 96 (the official recommended value).
"""
assert img.ndim == 2, ('Input image must be a gray or Y (of YCbCr) image with shape (h, w).')
# crop image
h, w = img.shape
num_block_h = math.floor(h / block_size_h)
num_block_w = math.floor(w / block_size_w)
img = img[0:num_block_h * block_size_h, 0:num_block_w * block_size_w]
distparam = [] # dist param is actually the multiscale features
for scale in (1, 2): # perform on two scales (1, 2)
mu = convolve(img, gaussian_window, mode='nearest')
sigma = np.sqrt(np.abs(convolve(np.square(img), gaussian_window, mode='nearest') - np.square(mu)))
# normalize, as in Eq. 1 in the paper
img_nomalized = (img - mu) / (sigma + 1)
feat = []
for idx_w in range(num_block_w):
for idx_h in range(num_block_h):
# process ecah block
block = img_nomalized[idx_h * block_size_h // scale:(idx_h + 1) * block_size_h // scale,
idx_w * block_size_w // scale:(idx_w + 1) * block_size_w // scale]
feat.append(compute_feature(block))
distparam.append(np.array(feat))
if scale == 1:
img = imresize(img / 255., scale=0.5, antialiasing=True)
img = img * 255.
distparam = np.concatenate(distparam, axis=1)
# fit a MVG (multivariate Gaussian) model to distorted patch features
mu_distparam = np.nanmean(distparam, axis=0)
# use nancov. ref: https://ww2.mathworks.cn/help/stats/nancov.html
distparam_no_nan = distparam[~np.isnan(distparam).any(axis=1)]
cov_distparam = np.cov(distparam_no_nan, rowvar=False)
# compute niqe quality, Eq. 10 in the paper
invcov_param = np.linalg.pinv((cov_pris_param + cov_distparam) / 2)
quality = np.matmul(
np.matmul((mu_pris_param - mu_distparam), invcov_param), np.transpose((mu_pris_param - mu_distparam)))
quality = np.sqrt(quality)
quality = float(np.squeeze(quality))
return quality
@METRIC_REGISTRY.register()
def calculate_niqe(img, crop_border, input_order='HWC', convert_to='y', **kwargs):
"""Calculate NIQE (Natural Image Quality Evaluator) metric.
``Paper: Making a "Completely Blind" Image Quality Analyzer``
This implementation could produce almost the same results as the official
MATLAB codes: http://live.ece.utexas.edu/research/quality/niqe_release.zip
> MATLAB R2021a result for tests/data/baboon.png: 5.72957338 (5.7296)
> Our re-implementation result for tests/data/baboon.png: 5.7295763 (5.7296)
We use the official params estimated from the pristine dataset.
We use the recommended block size (96, 96) without overlaps.
Args:
img (ndarray): Input image whose quality needs to be computed.
The input image must be in range [0, 255] with float/int type.
The input_order of image can be 'HW' or 'HWC' or 'CHW'. (BGR order)
If the input order is 'HWC' or 'CHW', it will be converted to gray
or Y (of YCbCr) image according to the ``convert_to`` argument.
crop_border (int): Cropped pixels in each edge of an image. These
pixels are not involved in the metric calculation.
input_order (str): Whether the input order is 'HW', 'HWC' or 'CHW'.
Default: 'HWC'.
convert_to (str): Whether converted to 'y' (of MATLAB YCbCr) or 'gray'.
Default: 'y'.
Returns:
float: NIQE result.
"""
ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
# we use the official params estimated from the pristine dataset.
niqe_pris_params = np.load(os.path.join(ROOT_DIR, 'niqe_pris_params.npz'))
mu_pris_param = niqe_pris_params['mu_pris_param']
cov_pris_param = niqe_pris_params['cov_pris_param']
gaussian_window = niqe_pris_params['gaussian_window']
img = img.astype(np.float32)
if input_order != 'HW':
img = reorder_image(img, input_order=input_order)
if convert_to == 'y':
img = to_y_channel(img)
elif convert_to == 'gray':
img = cv2.cvtColor(img / 255., cv2.COLOR_BGR2GRAY) * 255.
img = np.squeeze(img)
if crop_border != 0:
img = img[crop_border:-crop_border, crop_border:-crop_border]
# round is necessary for being consistent with MATLAB's result
img = img.round()
niqe_result = niqe(img, mu_pris_param, cov_pris_param, gaussian_window)
return niqe_result
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