# meaning of frequency domain for images and video

Started by August 3, 2005
```hi,
ive seen that transforms takes signals from time domain to frequency
domain. this case is evident in audio and speech coding. but what does
frequency mean in images and video? is there something similar to
oscillations as in audio signals in freq domain.

TIA..

--

```
```jagadeeshbp@gmail.com wrote:
> hi,
>   ive seen that transforms takes signals from time domain to frequency
> domain. this case is evident in audio and speech coding. but what does
> frequency mean in images and video? is there something similar to
> oscillations as in audio signals in freq domain.
>
> TIA..
>
> --

That's an interesting question with an interesting answer. It's easy to
imagine a picture that consists of a series of parallel bars in some
direction. A Ronchi grating is an example with a square intensity
profile, and sinusoidal profiles are possible. Frequency in picture land
is measured not in cycles per second, but in cycles per unit length.

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```Jerry Avins wrote:
> > hi,
> >   ive seen that transforms takes signals from time domain to frequency
> > domain. this case is evident in audio and speech coding. but what does
> > frequency mean in images and video? is there something similar to
> > oscillations as in audio signals in freq domain.
> >
> > TIA..
> >
> > --
>
> That's an interesting question with an interesting answer. It's easy to
> imagine a picture that consists of a series of parallel bars in some
> direction. A Ronchi grating is an example with a square intensity
> profile, and sinusoidal profiles are possible. Frequency in picture land
> is measured not in cycles per second, but in cycles per unit length.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF

Thank you for that reply. Im still a beginner in DSP. I cant get how a
cycle comes into picture. Is it the length over which the a pixel value
goes from black to white and then back or vice versa. Or is it
something else. Again how can I see that Ronchi grating has a square
intensity profile as you had mentioned.

--

```
```jagadeeshbp@gmail.com wrote:

...

>                                                       I can't get how a
> cycle comes into picture. Is it the length over which the a pixel value
> goes from black to white and then back or vice versa. Or is it
> something else. Again how can I see that Ronchi grating has a square
> intensity profile as you had mentioned.

A cycle is exactly what you imagine; the distance from crest to crest or
trough to trough. Unless the grating is parallel to an axis, the
wavelength along an axis is greater than the wavelength measured along a
line normal to the grating lines. One needs to be careful what one calls
THE wavelength (or its reciprocal, spatial frequency.

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```Jag,

find a old video test pattern that has resolution wedges and is