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CFA demosaicing examples

 
 
eawckyegcy@yahoo.com
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      02-06-2004
Most people probably just look at what comes out of their camera.
(Some even worship it!) But it is instructive nonetheless to examine
different interpolation approaches. I just stumbled onto this:

http://www.dmmd.net/Research/index.htm

Click on "demosaicing" underneath "Image Processing". There are a
small number of simulations of poor to excellent interpolation. (The
"fence" is a whopper; look at how good the interpolator handled that
chirp!) While you can tell the difference between the high-quality
algorithm and the "original", note how carefully you have to inspect
the results. Ask yourself the question: if the "DMMD" version came
out of a camera, would you be able to tell a CFA was in use? Or
suppose someone presented a field of (say) 30 images, a mixture of
"original" and interpolates of undisclosed originals and a limited
examination time; how many do you think you could correctly identify?
(An interesting experiment! Hmmm...)
 
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Bart van der Wolf
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      02-06-2004

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
SNIP
> (An interesting experiment! Hmmm...)


It is. That's why I did an experiment (
http://www.xs4all.nl/~bvdwolf/main/f.../bayer_cfa.htm ) with an alpha
version of their reconstruction implementation on an extremely critical
image. The target used is sharper than one can expect from a camera with a
lens and anti-aliasing filter, so I also simulated that influence.

Bart


 
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Dave Martindale
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      02-08-2004
"Bart van der Wolf" <(E-Mail Removed)> writes:

>It is. That's why I did an experiment (
>http://www.xs4all.nl/~bvdwolf/main/f.../bayer_cfa.htm ) with an alpha
>version of their reconstruction implementation on an extremely critical
>image. The target used is sharper than one can expect from a camera with a
>lens and anti-aliasing filter, so I also simulated that influence.


If you'd like to simulate a real antialiasing filter, instead of using
just Gaussian blur, do this:

Copy the original image and paste the copy on top of the original,
shifted one pixel left or right. Add the two images giving each 50%
weighting. Then take the result and repeat the process again, making
the offset one pixel up or down this time. This accurately simulates at
least one particular type of AA filter. The one-pixel offset guarantees
that the response at 0.5 cycles/pixel is exactly zero.

You may still want to do a small amount of Gaussian blur, to simulate
lens blur, before the AA filter simulation.

Dave
 
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Bart van der Wolf
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      02-08-2004

"Dave Martindale" <(E-Mail Removed)> wrote in message
news:c03vvl$no7$(E-Mail Removed)...
SNIP
> If you'd like to simulate a real antialiasing filter, instead of using
> just Gaussian blur, do this:


Thanks for the suggestion.

Bart


 
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