Re: [APML] High Pass Filter technique (WAS:New TP images)

[Wei-Hao Wang <whwang@gmail.com>]

Hi Alan,

In photoshop, maybe you can try to run a high pass filter over an 
image to see what you get.  

Basically what happens is, photoshop (Gaussian) blurs the image 
and subtract the blurred image from the original.  In other words, the 
high pass filter does exactly the opposite thing as Gaussian blur.
If you duplicate an image into two copies, Gaussian blur one, high 
pass the other one (both using the same radius), and add the blurred
and high passed image together, you will get an image identical to 
the original one.  This tells us that any image can be subdivided into
two components, a high passed component and a blurred component.

The simplest application of a high passed image is adding it back to the
orignal.  This is identical to a 100% strength unsharp mask.  The whole 
idea of unsharp mask is to change the weights of the high passed 
component and the blurred component.  Standard photoshop unsharp
mask increases the weight of the high passed component.  The "true 
unsharp mask" decreases the weight of the blurred component.  Indeed,
there is no difference between these two.

Of course, you can use the high passed images in many different ways,
using the layer function or the apply image function.

Hope this helps.

Cheers,
Wei-Hao

On 5/13/05, Alan Voetsch <alanv12952@yahoo.com> wrote:
> Hey Stuart,
> 
> --- Stuart Heggie <Stuart.J.Heggie@sympatico.ca> wrote:
> > I have been helped a lot by being taught how
> > to use
> > the High Pass Filter technique. I tried it on your jpeg and it made a
> > big improvement ( I think! ).
> 
> Do you have any further advice or suggestions on how to use this tool?
> 
> Thanks,
> Alan
> 


-- 
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Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:                       
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