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POimnoise('gaussian') underlying equations clarification
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  1. POimnoise('gaussian') underlying equations clarification
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    copied!<p>In MATLAB’s <code>imnoise()</code> function, when the type of noise is 'speckle', the documentation clearly states that it is multiplicative noise and states the underlying equation. </p> <blockquote> <p>J = imnoise(I,'speckle',v) adds multiplicative noise to the image I, using the equation <strong>J = I+n*I</strong>, where n is uniformly distributed random noise with mean 0 and variance v. The default for v is 0.04.</p> </blockquote> <p>However, no such equation is provided for the gaussian option. And there is a separate type called 'localvar'. So the equation when using <code>imnoise(I, gaussian, mean_noise, variance_noise)</code> should be </p> <blockquote> <p>J(x,y) = I(x,y) + g(mean_noise, sqrt((variance_noise)) </p> </blockquote> <p>Further, my assumptions:</p> <ol> <li>This noise <code>g</code> is not correlated to the spatial coordinates of the image </li> <li>This noise <code>g</code> is not correlated to the intensities at those spatial coordinates </li> <li><code>g</code> is a gaussian random number generated from a gaussian distribution of mean <code>mean_noise</code> and standard deviation <code>sigma = sqrt(variance_noise)</code></li> </ol> <p>Am I right? </p> <p><em>MAJOR UPDATE</em><br> I am unaccepting the previous answer to clear some confusion.So i checked the code for 'imnoise' in matlab and what it does is: </p> <blockquote> <p>b = a + sqrt(p4)*randn(sizeA) + p3; where<br> b - image with noise added<br> a - original image<br> p4 - variance<br> p3 - mean </p> </blockquote> <p>What is the range of randn()? I checked randomly and this produces values higher than 1 like 1.85. And the documentation for randn() fails to mention anything about the range. This is quite strange.</p>
 

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