Obviously there is no answer for this "Given this standard deviation how many filter samples are needed?" for all images. For example given a SD of 15, you'll never achieve that in a uniform image no matter how many samples you take. Even for images WITH an SD of 15 you'll never achieve that. So you're going to have to restate your question.

0 |

5/13/2010 10:25:54 AM

On May 13, 12:25=A0pm, ImageAnalyst <imageanal...@mailinator.com> wrote: > Obviously there is no answer for this "Given this standard deviation > how many filter samples are needed?" for all images. =A0For example > given a SD of 15, you'll never achieve that in a uniform image no > matter how many samples you take. =A0Even for images WITH an SD of 15 > you'll never achieve that. =A0So you're going to have to restate your > question. Thanks for the quick reply. I don't exactly follow. To make it clearer for me could you please explain what a filter sample is and how it relates to standard deviation? The image is the standard "cameraman" image (512x512 grayscale), which I am smoothing using a Gaussian filter with SDx=3D3,SDy=3D3. I don't know if this changes the question.

0 |

5/13/2010 10:47:49 AM

> > Secondly, what is the relationship between standard deviation and > filter samples? The question I need to answer is as follows: "Given > this standard deviation how many filter samples are needed?" If > someone could point me in the right direction, that would be great. I like to select the window size that is about 3*sigma in each side: n = ceil(6*sigma+1) And to enforce minimum of 3, n = max(ceil(6*sigma+1), 3) Bruno

0 |

5/13/2010 11:14:07 AM

On May 13, 6:47=A0am, J B <trifinit...@googlemail.com> wrote: > On May 13, 12:25=A0pm, ImageAnalyst <imageanal...@mailinator.com> wrote: > > > Obviously there is no answer for this "Given this standard deviation > > how many filter samples are needed?" for all images. =A0For example > > given a SD of 15, you'll never achieve that in a uniform image no > > matter how many samples you take. =A0Even for images WITH an SD of 15 > > you'll never achieve that. =A0So you're going to have to restate your > > question. > > Thanks for the quick reply. > > I don't exactly follow. To make it clearer for me could you please > explain what a filter sample is and how it relates to standard > deviation? > > The image is the standard "cameraman" image (512x512 grayscale), which > I am smoothing using a Gaussian filter with SDx=3D3,SDy=3D3. I don't know > if this changes the question. ---------------------------------------------------------------------------= --------------------------- Never mind - I got the standard deviations confused. I thought you were trying to get a certain specified SD in the image after you filtered it, but you were actually talking about the width of the Gaussian kernel. Did you see the additional option in the help for fspecial?? "h =3D fspecial('gaussian', hsize, sigma) returns a rotationally symmetric Gaussian lowpass filter of size hsize with standard deviation sigma (positive). hsize can be a vector specifying the number of rows and columns in h, or it can be a scalar, in which case h is a square matrix. The default value for hsize is [3 3]; the default value for sigma is 0.5." hsize is basically the window width of the kernel you're going to scan with, for example 21 pixels by 21 pixels, or 100 by 100. sigma is the width of the Gaussian shape that falls inside that window, for example 3 pixels. Understand now? Obviously you don't need the window width to be much wider than about 6 or 7 sigmas because the Guassian will flatten out by the time it gets to the edge.

0 |

5/13/2010 2:47:44 PM

Hi all, This is a continuum of the question I post one moment ago. I've obtained a 11x11 impulse response for that 2D low pass Butterworth filter of 7th order and 0.2 cutoff frequency(normalized frequency range [-0.5, 0.5])... My friend claimed that the following 11x11 h impulse response have negative values in it so it is no good for image filtering... (btw, why are there negative values? ) He suggests that I forget these fancy filters and use a plain Gaussian filter for low pass filtering... however I looked into the "fspecial" command in Matlab image toolbox... and I ...

Dear members, I would like to inform you that we have released our last version of the open source library "Filters". We will appreciate your feedback. link : http://filters.sourceforge.net/ Regards In short, no source code = crap. Come back when you've got something real to download, a few demos and some API's don't equate to much these days... edurand wrote: > Dear members, > I would like to inform you that we have released our last version of > the open source library "Filters". We will appreciate your feedback. > link : http://filters.so...

hi to all Im new to image processing and also to matlab. I have a project which needs to extract blood vessels from retinal image by using matched filtering and It looks like I have to desgin one but I have no idea what is a matched filter. Can some please explain me image processing with matched filtering thank you ANIL Why do you need to use a matched filter? Why not use any method that you can think of that will work? If it's your homework problem, then review your notes from the class lectures or ask your professor. If you have a MATLAB question, such as how to use im...

I want to smooth an image using an isotropic Gaussian filter with standard deviation of =F3x, =F3y =3D 3. To achieve this, can I use the fspecial function to create the smoothing filter as follows: gauss_filter =3D fspecial('gaussian', [x y], 3); With [x y] being the size of the filter to apply to the image. If not, what should I be using instead? Also, what is the relationship between the number of filter samples required and the standard deviation used? Thanks. ...

I must do a Gaussian Filter on image, I have matrix data image in a 100x100 matrix. I generate a 7x7 gaussian matrix for filtering, how do I padding the gaussian matrix for obtain a 100x100 matrix ? with zeros value around gaussian value ? thank you so much. anyone can help me ? ...

Dear members: I am given a continous filter h(x,y) and I should use this filter to filter a discrete image x(m,n) in MATLAB. In my thinking, the first task should be to sample the continous filter. Is it corresponding to the task of choosing the length of the filter? And how can we choose an effective length of the filter? To avoid the aliasing, the filter should be sampled with a sampling frequency equal or greater than two time of the maximum frequency of the image (Nyquist freq). The problem is that how I know the maximum frequency of the image? Should I low pass filter the image first a...

Hi, I am a newbie in matlab and dsp. I have a signal and would like to generate gaussian noise and use a gaussian filter to remove the noise. From what i have gathered from matlab, to generate gaussian noise i would use randn(1,256) to generate gaussian noise and add it to my signal. However, i am not certain on how to remove the gaussian noise i have generated. Any help is greatly appreciated on how to generate the filter. My code would be : noise=radn(1,256); signal=orginalsignal.*noise; Thanks. Newbie ...

dear all, I am facing the following problem that I need your help: We have in our experiments some special images need to be processed. My task is to look at these images and see how to improve/enhance them. In fact we/I have no idea on how much enhancement we can get. So what I've done in the past month is to play with different kind of filters to try on the images. We use PSNR as judgement. It turns out I found a Gaussian 3x3 filter has particularly high enhancement to the images, comparing with other filters provided by Matlab, such as "laplacian", "averaging"... ...

Is it possible to use dlmwrite within a loop ? my code is bit long, but i am stuck here .... loop starts { file taken as input some processing done over it results saves in a varaible "d" now i want to save the results of d to new text file display the results on matlab loop goes to next file until last file } for a single file without loop, this works fine dlmwrite('test.txt',d); now what to do within loop to save the results every time with new file name, as every time new file is processing like dlmwrite('file1.txt',d); dlmwri...

Hi, I'm a student.I want to do thesis from the next semester on genetic imaging.So for that I want to learn MATLAB for that and I don't have version 7.0.Can anybody suggest me where to start and how to start. Thanks in advance. pallavi. palllavi mamilla wrote: > > > Hi, > > I'm a student.I want to do thesis from the next semester on > genetic imaging.So for that I want to learn MATLAB for that and I > don't have version 7.0.Can anybody suggest me where to start and > how > to start. > > Thanks in advance. > > pallavi. I have only ...

Hello, I am using MATLAB to demonstrate how images can be manipulated but I have got a bit stuck. I want to demonstrate everything by using the binary of an image only. The idea is that eventually the program will show the original image, then the program will perform some binary arithmatic before showing the new manipulated image alongside the original. For this, I need a way of taking the first pixel, executing an algorithm, moving to the next pixel, performing maybe a slightly different algorithm, etc... But for this, I want to store the resulting value as the first pixel and second pixel...

I am New to matlab I want to read the video from webcam for that i need the code and my device id appears like this {1x0 cell} how can i specify the device id? If the device ID is empty, then the camera is not detected by MATLAB. Are you able to use it outside of MATLAB? What is your webcam model/name? What version of MATLAB are you using? Beginning R2014a, we added support for USB Webcams through base MATLAB. http://www.mathworks.com/matlabcentral/fileexchange/45182-matlab-support-package-for-usb-webcams Thanks. "yenosh Tummala" <yenoshk4@gmail.com> wrote in m...

i want to specified an elemet of image matrix (when i read the image with imread()and show it with imshow() i want when i click on the image the elemet of image matrix of the point [x,y,z]that i've click on be returned!!!!!). iwant to specify 4 feature point on an image and track them on the next imges!! rima wrote: > > > i want to specified an elemet of image matrix (when i read the > image > with imread()and show it with imshow() i want when i click on the > image the elemet of image matrix of the point [x,y,z]that i've > click > on be returned!!!!!). iwant t...

I don't know matlab and I begin to learn matlab for this project I need to understand every line in this code now I don't understand anything I don't understand the commands in this code and I will glad if anybody can help me to understand what is write in this code or give me a link that explain any commands that appear in this code Maybe this is a pseudo code ?? This code need to recognize fingerprint In the first picture http://img22.imageshack.us/img22/841/matlaba1.jpg I know that the first paragraph load image from memory stockpile The second paragraph does a histogram The...

Resources last updated: 1/24/2016 6:26:01 AM