Path: news.mathworks.com!newsfeed-00.mathworks.com!newsfeed2.dallas1.level3.net!news.level3.com!postnews.google.com!v8g2000yqe.googlegroups.com!not-for-mail From: ImageAnalyst <imageanalyst@mailinator.com> Newsgroups: comp.soft-sys.matlab Subject: Re: Generate noise model[Please help] Date: Sat, 21 Aug 2010 14:38:55 -0700 (PDT) Organization: http://groups.google.com Lines: 29 Message-ID: <3d735524-57af-4868-b7d3-640a51651380@v8g2000yqe.googlegroups.com> References: <2039352140.31930.1282248289923.JavaMail.root@gallium.mathforum.org> <839084457.41217.1282394676124.JavaMail.root@gallium.mathforum.org> NNTP-Posting-Host: 184.57.134.178 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1282426735 31105 127.0.0.1 (21 Aug 2010 21:38:55 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Sat, 21 Aug 2010 21:38:55 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: v8g2000yqe.googlegroups.com; posting-host=184.57.134.178; posting-account=0rLUzAkAAABojYSRC64DkTbtiSCX77HH User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8,gzip(gfe) Xref: news.mathworks.com comp.soft-sys.matlab:663995 On Aug 21, 8:44 am, Daniel <rome...@hotmail.com> wrote: > I am sorry I think you get me wrong.The problem is about image processing not mathematic.I need to read in an image and generate the Rayleigh noise model from the image given that the noise is model by the pdf as written in the link belowhttp://www.bioen.utah.edu/wiki/index.php?title=Noise_modeling_and_Pro......pls help..thx ---------------------------------------------------------- Daniel: I don't think I got you wrong. I gave you the general method for getting random numbers taken from whatever distribution you want. Basically you integrate the pdf to get the cdf, invert it, and plug in a uniform distribution. And I gave code to do that. That's the basic recipe that will work for any pdf. Of course it's easier if you know the analytical form for the noise, like we do for the Rayleigh (I took it from the website Walter mentioned.) But you could do it numerically if you had only an empirical pdf function. What you have not given is how that noise relates to the pixel value. Is it additive noise, where all the Rayleigh noise comes from the same distribution with some mean that is independent of the pixel value? Or is it value-dependent noise, for example the mean of the Rayleigh distribution should be the pixel value, and so you need to adjust your noise-generating function for a new mean each time you encounter a new pixel value? Can you answer that? Because there is no "right" answer that I know of. I suspect it may be the latter but you could define it to work however you want - not that that necessarily corresponds with reality, but you could do it. ImageAnalyst