Steve on Image Processing

Results for: Fourier transforms

Fourier transforms, vertical lines, and horizontal lines 13

Posted by Steve Eddins,

Fourier transforms, vertical lines, and horizontal lines  A reader asked in a blog comment recently why a vertical line (or edge) shows up in the Fourier transform of an image as a horizontal line. I thought I would try to explain this using the simplest example I could think... read more >>

Complex surprises from fft 7

Posted by Steve Eddins,

Complex surprises from fft  One of the discrete-time Fourier transform properties that many people learn is that if a sequence is conjugate symmetric, , then the Fourier transform is real. Therefore it surprises people sometimes when the output of fft... read more >>

Plotting the DTFT using the output of fft 6

Posted by Steve Eddins,

Plotting the DTFT using the output of fft  In my Fourier transform series I've been trying to address some of the common points of confusion surrounding this topic. For today's espisode I want to look at how to use the fft function to produce discrete-time Fourier transform (DTFT) magnitude... read more >>

Negative frequencies 10

Posted by Steve Eddins,

Negative frequencies  I recently asked for your advice about how to continue my Fourier transform series. I appreciate all the enthusiastic and helpful responses. I'd like to continue focusing on some basic points that confuse folks who don't have an extensive signal processing background: ... read more >>

Fourier transforms – where to go from here 26

Posted by Steve Eddins,

Fourier transforms – where to go from here  Last fall I started posting occasionally about Fourier transforms. This topic causes much confusion, which is particularly unfortunate given how many people are interested in it. I speculate that the fundamental source of confusion is that there are really several different (but... read more >>

No units in the DTFT 4

Posted by Steve Eddins,

No units in the DTFT  OysterEngineer (I love that name!) asked some interesting questions in response to my last Fourier transform post, which concerned the relationship between the discrete-time Fourier transform (DTFT) and the discrete Fourier transform (DFT). I'd like to first tackle OE's comments about units.... read more >>

The DFT and the DTFT 8

Posted by Steve Eddins,

The DFT and the DTFT  It's finally time to start looking at the relationship between the discrete Fourier transform (DFT) and the discrete-time Fourier transform (DTFT). Let's look at a simple rectangular pulse, for . The DTFT of is: ... read more >>

Aliasing and a sampled cosine signal 22

Posted by Steve Eddins,

Aliasing and a sampled cosine signal  One challenge of teaching Fourier transform concepts is that each concept can be (and is) interpreted and explained in many different ways. It isn't always obvious how the different explanations for the same concepts are connected. For... read more >>

Aliasing and the discrete-time Fourier transform 10

Posted by Steve Eddins,

Aliasing and the discrete-time Fourier transform  Many of you were onto me immediately last week. I asked you to estimate the frequency of the sampled cosine signal below, and readers quickly chimed in to guess that this question was really a teaser about aliasing. ... read more >>

Sampling a cosine 12

Posted by Steve Eddins,

Sampling a cosine  I know, I know ... I've really fallen behind in my blog posting the last month or so. Shifting responsibilities in my "real job" have left me snowed under for the last few weeks, and I haven't figured out yet how... read more >>

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