I have a signal that contains three distinct images, this means that I have three frequencies or peaks, and each one corresponds to a picture.

I have a function that converts a signal into an image. I'm using the low pass, high pass, and band pass filters in Matlab to filter out the frequencies I want. When I use the LP filter, the image I get is clear. But when I use both the HP and BP filter, the images I get are not clear/(contain noise?). I'm using the "butter" and "filter" functions. I'm not really sure how to clear up the images or if I'm doing the wrong steps. What I'm doing is using the filter, then using a tdft function, then I plot that and use the signal-to-image function I have to get the image. I'd appreciate any help.


Signal with all three images: enter image description here

TDFT of image: enter image description here

First image after lowpass: enter image description here

Second image after bandpass: enter image description here

  • $\begingroup$ Your question lacks a lot of context and details. It's entirely unclear how your signal and your pictures are related to start with. $\endgroup$ – Jazzmaniac May 20 '15 at 11:15
  • $\begingroup$ Could you post some examples and explain what is not clear in the images? $\endgroup$ – JRE May 20 '15 at 11:45
  • $\begingroup$ Well, the signal contains the information that is then converted into images. It contains the info for the 3 pictures, meaning I need to isolate each 'peak'. I'm not really sure how to explain that in more detail. As for the code, I'm mostly going with : [b,a] = butter(9,0.3,'low'); Y = filter(b,a,z); Y_t = tdftfast(Y); figure plot(nu,abs(Y_t)) title('LOW') figure present_image(Y) %function I got from my teacher I use this with low,high and band pass. As to what is not clear in the picture, I guess it's that it's got grey lines going across the image. $\endgroup$ – Bassam May 20 '15 at 11:59
  • $\begingroup$ Could you please post the images? If you can't put them directly into the question, then post them somewhere and put links to them in your question and someone here can edit them into your question $\endgroup$ – JRE May 20 '15 at 12:20
  • $\begingroup$ signal with all three images: imgur.com/jhKYMGT , how it looks likes with tdft: imgur.com/tMIMimt , first image with low pass filter: imgur.com/PQ78Yce , second image when using a bandpass filter : imgur.com/vMmOakA . $\endgroup$ – Bassam May 20 '15 at 12:40

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