FFTW, Imlib & OpenCV

>sunderam wrote:
>> The FT of ima for this signal i would calc
>> 1.mean intensity
>> 2.std deviation
>> Sunderam
>> ge would give me a signal.
>
>Neither intensity nor its standard deviation is measured in the
>frequency domain. For that, you want not the FT, but the original
>signal.
>
>What is "ge"?
>
>Jerry
>
>
How do i get the original signal given an image? I though the FT of image
would give me the original signal.

ge was the remaining part of ima which should have been image.

I m just calculating the contrast. This paragraph is taken from a paper
about image quality assesment by using the human visual system.
 
The following paragraph is what i m trying to achive

" Suppose x and y are two non� negative image signals, which have been
aligned with each other (e.g., spatial patches extracted from each image).
If we consider one of the signals to have perfect quality, then 
the similarity measure can serve as a quantitative measure� 
ment of the quality of the second signal. The system separates the task of
similarity measurement into three comparisons: luminance, contrast and
structure. First, the luminance of each signal is compared. Assuming
discrete signals, this is estimated as the mean intensity: 
The luminance comparison function l(x, y) is then a function of � x and �
y 
Second, we remove the mean intensity from the signal. 
In discrete form, the resulting signal x-� x corresponds to 
the projection of vector x onto the hyperplane defined by the formula.
We use the standard deviation (the square root of variance) 
as an estimate of the signal contrast. An unbiased estimate 
in discrete form is given by the formula"


Sunderam

		
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You still have no clue, and you don't bother to take our advice.  Why
should we bother?

Ciao,

Peter K.

Hello Peter,

You had mentioned that contrast could be calculated using I(x,y,p). I
agree to that part.. 
Can you please tell me why does the author say two nonnegatie signals
rather than just talking about I(x,y,p).There must be some premise behind
using the  term signal. I m still trying to understand and comprehend why
use the "signal" if its out of context.

Because i had no clue thats why i posted my query here otherwise would not
have.
Sunderam 

>You still have no clue, and you don't bother to take our advice.  Why
>should we bother?
>
>Ciao,
>
>Peter K.
>
>


		
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sunderam wrote:
> Hello Peter,
>
> You had mentioned that contrast could be calculated using I(x,y,p). I
> agree to that part..
> Can you please tell me why does the author say two nonnegatie signals
> rather than just talking about I(x,y,p).There must be some premise behind
> using the  term signal. I m still trying to understand and comprehend why
> use the "signal" if its out of context.

Negative brightness doesn't exist. Therefore, all legitimate intensity
samples are non-negative. All physical weights are non-negative too.

> Because i had no clue thats why i posted my query here otherwise would not
> have.
> Sunderam
>
> >You still have no clue, and you don't bother to take our advice.  Why
> >should we bother?

Sunderam,

These quoted messages would be easier to read if you put your replies
either after the material you reply to or intersperced within it, as
appropriate.

It's clear that you have no clue. The discouraging part is that you
have a fixed false idea that no advice -- Peter K's term -- can
correct. Here it is again. Read it slowly:

Unless you consider the light focused on a sensor, or a document in a
scanner, you never work with an image. Instead, you work with a signal
that represents it -- encodes it, if you like. A color image is
represented by three intensities at each point. (Various sets of three
are sufficient.)

These intensities suffice to determine contrast, mean intensity and
most other measures of the image that interest you. They are a signal,
not an image. Since the signal represents an image, it is often
erroneously called an image, just as the bits on a CD and the wavy
grooves on a vinyl recording are often called music.

The 2D FT of the intensities show another aspect of the image, a useful
one, but not one that helps with the qualities you want to assess. Get
over it!

Jerry

I get it 
thanks for all the help
sunderam

>
>
>sunderam wrote:
>> Hello Peter,
>>
>> You had mentioned that contrast could be calculated using I(x,y,p). I
>> agree to that part..
>> Can you please tell me why does the author say two nonnegatie signals
>> rather than just talking about I(x,y,p).There must be some premise
behind
>> using the  term signal. I m still trying to understand and comprehend
why
>> use the "signal" if its out of context.
>
>Negative brightness doesn't exist. Therefore, all legitimate intensity
>samples are non-negative. All physical weights are non-negative too.
>
>> Because i had no clue thats why i posted my query here otherwise would
not
>> have.
>> Sunderam
>>
>> >You still have no clue, and you don't bother to take our advice.  Why
>> >should we bother?
>
>Sunderam,
>
>These quoted messages would be easier to read if you put your replies
>either after the material you reply to or intersperced within it, as
>appropriate.
>
>It's clear that you have no clue. The discouraging part is that you
>have a fixed false idea that no advice -- Peter K's term -- can
>correct. Here it is again. Read it slowly:
>
>Unless you consider the light focused on a sensor, or a document in a
>scanner, you never work with an image. Instead, you work with a signal
>that represents it -- encodes it, if you like. A color image is
>represented by three intensities at each point. (Various sets of three
>are sufficient.)
>
>These intensities suffice to determine contrast, mean intensity and
>most other measures of the image that interest you. They are a signal,
>not an image. Since the signal represents an image, it is often
>erroneously called an image, just as the bits on a CD and the wavy
>grooves on a vinyl recording are often called music.
>
>The 2D FT of the intensities show another aspect of the image, a useful
>one, but not one that helps with the qualities you want to assess. Get
>over it!
>
>Jerry
>
>


		
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Can you please give me a pointer where i could find the documentation about
the contrast calculation you mentioned. I can get my facts straight that
way
Sunderam

>] Then my question, is there a method to represent
>] an image in terms of signal in frequency domain.?
>
>Why do you want to?
>
>If you're trying to work out the contrast of an image, and you have the
>image pixel values, then you don't need to do much at all.
>
>If you have an image, then the pixel values are usually represented as:
>
>I(x,y,p) = 0 to 255
>
>where "x" is the x position,
>"y" is the y position, and
>"p" is the plane (e.g. red, green, blue, alpha).
>
>It is this I(x,y,p) that you need to calculate the contrast.
>
>] And how can i find contrast for image of
>] any format, not restricted to jpeg formats only.
>
>Why do you think that a contrast calculation depends on the image
>format?
>
>All image storage formats need, eventually, to reconstitute the signal
>into the I(x,y,p) information.
>
>You appear to be very confused.  Please keep asking questions so we can
>sort out your confusion.
>
>Start with the basics: you don't appear to comprehend image formats
>yet.  Get that right before moving on to anything else more
>complicated... you need to crawl before you can run.
>
>Ciao,
>
>Peter K.
>
>


		
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sunderam wrote:
> Hello Peter,
>
> You had mentioned that contrast could be calculated using I(x,y,p). I
> agree to that part..
> Can you please tell me why does the author say two nonnegatie signals
> rather than just talking about I(x,y,p).There must be some premise behind
> using the  term signal. I m still trying to understand and comprehend why
> use the "signal" if its out of context.

Um, I think you're making a mountain out of a molehill.  I(x,y,p) IS
the "signal" you're looking for.

> Because i had no clue thats why i posted my query here otherwise would not
> have.

Ciao,

Peter K.

Can you please give me a pointer where i could find the documentation
about
the contrast calculation you mentioned. I can get my facts straight that
way
Thanks
Sunderam
>sunderam wrote:
>> Hello Peter,
>>
>> You had mentioned that contrast could be calculated using I(x,y,p). I
>> agree to that part..
>> Can you please tell me why does the author say two nonnegatie signals
>> rather than just talking about I(x,y,p).There must be some premise
behind
>> using the  term signal. I m still trying to understand and comprehend
why
>> use the "signal" if its out of context.
>
>Um, I think you're making a mountain out of a molehill.  I(x,y,p) IS
>the "signal" you're looking for.
>
>> Because i had no clue thats why i posted my query here otherwise would
not
>> have.
>
>Ciao,
>
>Peter K.
>
>


		
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"sunderam" <jpothara@uccs.edu> writes:

>How do i get the original signal given an image? I though the FT of image
>would give me the original signal.

In image processing, the image *is* the signal.  You don't need to (and
in general cannot) get the original light flux in the scene.

>" Suppose x and y are two non&#4294967295; negative image signals, which have been
>aligned with each other (e.g., spatial patches extracted from each image).
>If we consider one of the signals to have perfect quality, then 
>the similarity measure can serve as a quantitative measure&#4294967295; 
>ment of the quality of the second signal.

Just replace "image signals" with "images" and "signal" with "image".
Then it should make sense to you.

	Dave