what does phase distortion look like in image processing?

I read the following in Matlab Help Document of Image Processing ToolBoxes,

"FIR filters can be designed to have linear phase, which helps prevent 
distortion. "

I am wondering what does phase distortion look like in image processing?

Also,

"Another class of filter, the infinite impulse response (IIR) filter, is not 
as suitable for image processing applications. It lacks the inherent 
stability and ease of design and implementation of the FIR filter. 
Therefore, this toolbox does not provide IIR filter support..."

I want to ask what kind of inherent stability issue does IIR filter have?

Thanks lot! 

lucy wrote:
> I read the following in Matlab Help Document of Image Processing ToolBoxes,
> 
> "FIR filters can be designed to have linear phase, which helps prevent 
> distortion. "
> 
> I am wondering what does phase distortion look like in image processing?
> 
> Also,
> 
> "Another class of filter, the infinite impulse response (IIR) filter, is not 
> as suitable for image processing applications. It lacks the inherent 
> stability and ease of design and implementation of the FIR filter. 
> Therefore, this toolbox does not provide IIR filter support..."
> 
> I want to ask what kind of inherent stability issue does IIR filter have?
> 
> Thanks lot! 
> 
> 
These questions are probably best answered by running some images 
through the applicable filters and seeing what the results are.  Just 
make yourself an all-pass filter with considerable phase distortion, 
filter your image, and take a look.

Similarly, you can either filter your image with an IIR by hand and see 
what it looks like, or you can whomp up a FIR filter with IIR-like 
characteristics, and see how _that_ looks.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott <tim@wescottnospamdesign.com> writes:

> ...or you can whomp up a FIR filter ...

"whomp up" - similar to "cook up" but usually performed
with more force and intention.
-- 
%  Randy Yates                  % "And all that I can do
%% Fuquay-Varina, NC            %  is say I'm sorry, 
%%% 919-577-9882                %  that's the way it goes..."
%%%% <yates@ieee.org>           % Getting To The Point', *Balance of Power*, ELO
http://home.earthlink.net/~yatescr

You'll get a fuzzier image than you started with, because some
of the frequency components in your image (sine waves) will
have their amplitude peaks at positions on your image that are
physically separated from where they were originally.

(Remember that we're talking about phase as a function of
distance or space, and not as a function of time.)

"lucy" <losemind@yahoo.com> wrote in message
news:cnbp9l$ftf$1@news.Stanford.EDU...
> I am wondering what does phase distortion look like in image processing?

lucy wrote:
> 
> I read the following in Matlab Help Document of Image Processing ToolBoxes,
> 
> "FIR filters can be designed to have linear phase, which helps prevent
> distortion. "
> 
> I am wondering what does phase distortion look like in image processing?

Motion blur (when the object being photographed or the camera moves
while the image is taken) is the most common example of phase
distortion. And of course, to counteract motion blur in an image one
would need to develop a filter with non-linear phase.


> 
> Also,
> 
> "Another class of filter, the infinite impulse response (IIR) filter, is not
> as suitable for image processing applications. It lacks the inherent
> stability and ease of design and implementation of the FIR filter.
> Therefore, this toolbox does not provide IIR filter support..."
> 
> I want to ask what kind of inherent stability issue does IIR filter have?

Well,  IIR's can be unstable, but I wouldn't say this is the main
problem with using them on images. Mostly they have (theoretically)
infinite support  while images are pretty short term with low dynamic
range. Also, IIR's do not have linear phase. Those would be most likely
the main reasons they are avoided.

-jim


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Randy Yates wrote:

> Tim Wescott <tim@wescottnospamdesign.com> writes:
> 
> 
>>...or you can whomp up a FIR filter ...
> 
> 
> "whomp up" - similar to "cook up" but usually performed
> with more force and intention.

I don't know where I picked that phrase up, but it sure fits with 
hacking out some quick little thing to solve a point problem.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"lucy" <losemind@yahoo.com> wrote in message news:<cnbp9l$ftf$1@news.Stanford.EDU>...
> I read the following in Matlab Help Document of Image Processing ToolBoxes,
> 
> "FIR filters can be designed to have linear phase, which helps prevent 
> distortion. "
> 
> I am wondering what does phase distortion look like in image processing?

Maybe something usefil in:

http://www.ysbl.york.ac.uk/~cowtan/fourier/fourier.html

Best regards,

Jon C.

On 2004-11-16 17:14:13 +0100, jg.campbell@ntlworld.com (Jonathan G 
Campbell) said:

> Maybe something usefil in:
> 
> http://www.ysbl.york.ac.uk/~cowtan/fourier/fourier.html
> 
> Best regards,
> 
> Jon C.

Hi Jon,

great link, thanks for posting!
-- 
Stephan M. Bernsee
http://www.dspdimension.com