Image quality assessment: Difference between revisions
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* WS-PSNR is a standard PSNR calculation where the mean squared error is weighted by the size of each pixel. | * WS-PSNR is a standard PSNR calculation where the mean squared error is weighted by the size of each pixel. | ||
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\begin{align} | \begin{align} | ||
WMSE &= \frac{1}{\sum_{i,j}w(i,j)} \sum_{i,j} (I_1(i,j)-I_2(i,j))^2 * w(i,j)\\ | WMSE &= \frac{1}{\sum_{i,j}w(i,j)} \sum_{i,j} (I_1(i,j)-I_2(i,j))^2 * w(i,j)\\ | ||
Revision as of 15:23, 27 August 2020
Methods for Image quality assessment
The standard metrics are mean-squared error, peak signal to noise ratio (psnr), and structural similarity (ssim).
Standard Images and Video
\(\DeclareMathOperator{\mean}{mean}\)
- MSE
- \[MSE = \mean((I_1 - I_2)^2)\]
- PSNR
- \[PSNR=10\log_{10}(\frac{R^2}{MSE})\]
- where R^2 is the maximum fluctuation (e.g. 1.0 for [0-1] float images, 255 for uint8).
- SSIM
Foveated Quality Assessment
- Lee et al.[1] propose Foveated signal to noise ratio (FSNR) which measures the signal to noise ratio in a curvilinear space. However they do not provide the exact equations to compute the curvilienar space.
Spherical Quality Assessment
- WS-PSNR is a standard PSNR calculation where the mean squared error is weighted by the size of each pixel.
- \(\displaystyle \begin{align} WMSE &= \frac{1}{\sum_{i,j}w(i,j)} \sum_{i,j} (I_1(i,j)-I_2(i,j))^2 * w(i,j)\\ WS\_PSNR &= 10\log_{10}(\frac{R^2}{WMSE})\\ \end{align} \)
- The weights are \(w(i,j) = \sin(\frac{j+0.5}{N}\pi) = \cos(\frac{j+0.5-N/2}{N}\pi)\).
- Yu et al.[2] propose Spherical PSNR (S-PSNR). In S-PSNR, points are randomly sampled on a sphere and back projected to the reference and reconstructed images. In practice, these randomly sampled points need to be saved for reproducibility. They use 655262 points which are available on their repo.
Samsung has a 360tools program which can compute WS-PSNR, S_PSNR,
Resources
References
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