Video quality assessment -- Step by step

VQA(Video quality assesment) is generated from image quality assessment.

Terminology

MSE

Mean Square Error

$$ MSE = \frac{1}{NM} \sum_{i=1}^N \sum_{j=1}^M (f(i,j) - f’(i,j))^2 $$

PSNR

Peak Signal to Noise Ratio

$$ PSNR = 10 \log \frac{MAX_I^2}{MSE} [dB] $$
where $MAX_I$ is the maximum pixel of the image.

SSIM

Structural Similarity Index Measure

$$ SSIM(x,y) = [l(x,y)]^\alpha \cdot [c(x,y)]^\beta \cdot [s(x,y)]^\gamma $$

$$ l(x,y) = \frac{2\mu_x\mu_y + C_1}{\mu_x^2 + \mu_y^2 + C_1’} $$

$$ c(x,y) = \frac{2\sigma_x\sigma_y + C_2}{\sigma_x^2 + \sigma_y^2 + C_2’} $$

$$ s(x,y) = \frac{\sigma_{xy} + C_3}{\sigma_x \sigma_y + C_3’} $$

VSSIM

Video Structure Similarity

$$ Q_i = \frac{\sum_{j=1}^{R_s} w_{ij} SSIM_{ij}}{\sum_{j=1}^{R_s} w_{ij}} $$

where i th frame, j th sampling window, w is the weight value. $R_s$ is quantity of sampling windows per video frame. And VSSIM for the entire video of length N is:

$$ VSSIM = \frac{\sum_{i=1}^N W_i Q_i}{\sum_{i=1}^N W_i} $$

PVQM

perceptual Video Quality Metric

Conducted using software in this article.

LCC & SROCC

These are two correlation factors(LCC is Pearson linear correlation coefficient and SROCC is spearman rank-order correlation coefficient) for evaluation of the similarity.

The very simple transfer is use the model and results from IQA. Just modify the input to a set of frames.

Ground truth

In machine learning, the term “ground truth” refers to the accuracy of the training set’s classification for supervised learning techniques. In another word, ground truth is a reference that we assume it totally right from empirical evidence.

SGD

It is an optimization function(regressor) based on the concepts of directional derivative of a multivariable differential function.

Full reference and no reference

The full reference method compares the raw image and the so-called distorted image. However, what if the reference image is not good enough? For no reference, it seems like it has no reference, but it has its standard in the heart.