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Acecliffy 09-15-2006 05:50 PM

Scanned Slides: Filtering non-uniform edge discolorations
 
MY SITUATION: I am scanning color slides that are 20 years old. They
have edge discoloration, meaning that the sides are somewhat darker
(perhaps blueish) than the center of the slide. This is not a problem
with my slide scanner; rather, it is inherent in the slides. I don't
know why they have this problem, since I am doing this job for my major
professor.

So... here is an example of what I am talking aoubt. There is a link
to a sample image here:
http://web.ics.purdue.edu/~racz/images/Image012.jpg

The concrete on the left should have roughly the same color as the
concrete in the center, but it has a blue tint (I believe, maybe it is
a mixture).

MY QUESTION: Is there a filter to adjust/perform color corrections for
non-uniformity such as this, where a hue/saturation/balance is
non-uniform across the image? It may be a linear gradient, or perhaps
even a circular/eliptical gradient?

Thanks in advance.


Rutger 09-15-2006 07:29 PM

Re: Scanned Slides: Filtering non-uniform edge discolorations
 
"Acecliffy" <clifford.racz@gmail.com> schreef in bericht
news:1158342622.248086.204770@i3g2000cwc.googlegro ups.com...
> MY SITUATION: I am scanning color slides that are 20 years old. They
> have edge discoloration, meaning that the sides are somewhat darker
> (perhaps blueish) than the center of the slide. This is not a problem
> with my slide scanner; rather, it is inherent in the slides. I don't
> know why they have this problem, since I am doing this job for my major
> professor.
>
> So... here is an example of what I am talking aoubt. There is a link
> to a sample image here:
> http://web.ics.purdue.edu/~racz/images/Image012.jpg
>
> The concrete on the left should have roughly the same color as the
> concrete in the center, but it has a blue tint (I believe, maybe it is
> a mixture).
>
> MY QUESTION: Is there a filter to adjust/perform color corrections for
> non-uniformity such as this, where a hue/saturation/balance is
> non-uniform across the image? It may be a linear gradient, or perhaps
> even a circular/eliptical gradient?
>
> Thanks in advance.
>


No problem: in PS, make a rectengular selection with a big feather, invert
the selection and correct with curves or any other means you like.

Rutger


--
http://www.flickr.com/photos/zwaarddrager/



stuseven@hotmail.com 09-15-2006 08:39 PM

Re: Scanned Slides: Filtering non-uniform edge discolorations
 
+ remember that you are looking at a slide... a transparency...
color fade in the jpg you posted is almost indiscernible. As
for the color cast, Gimp has numerous plug-ins which will
correct this.


Acecliffy wrote:
> MY SITUATION: I am scanning color slides that are 20 years old. They
> have edge discoloration, meaning that the sides are somewhat darker
> (perhaps blueish) than the center of the slide. This is not a problem
> with my slide scanner; rather, it is inherent in the slides. I don't
> know why they have this problem, since I am doing this job for my major
> professor.
>
> So... here is an example of what I am talking aoubt. There is a link
> to a sample image here:
> http://web.ics.purdue.edu/~racz/images/Image012.jpg
>
> The concrete on the left should have roughly the same color as the
> concrete in the center, but it has a blue tint (I believe, maybe it is
> a mixture).
>
> MY QUESTION: Is there a filter to adjust/perform color corrections for
> non-uniformity such as this, where a hue/saturation/balance is
> non-uniform across the image? It may be a linear gradient, or perhaps
> even a circular/eliptical gradient?
>
> Thanks in advance.



Mike Hyndman 09-16-2006 04:35 PM

Re: Scanned Slides: Filtering non-uniform edge discolorations
 

"Acecliffy" <clifford.racz@gmail.com> wrote in message
news:1158342622.248086.204770@i3g2000cwc.googlegro ups.com...
> MY SITUATION: I am scanning color slides that are 20 years old. They
> have edge discoloration, meaning that the sides are somewhat darker
> (perhaps blueish) than the center of the slide. This is not a problem
> with my slide scanner; rather, it is inherent in the slides. I don't
> know why they have this problem, since I am doing this job for my major
> professor.
>
> So... here is an example of what I am talking aoubt. There is a link
> to a sample image here:
> http://web.ics.purdue.edu/~racz/images/Image012.jpg
>
> The concrete on the left should have roughly the same color as the
> concrete in the center, but it has a blue tint (I believe, maybe it is
> a mixture).
>
> MY QUESTION: Is there a filter to adjust/perform color corrections for
> non-uniformity such as this, where a hue/saturation/balance is
> non-uniform across the image? It may be a linear gradient, or perhaps
> even a circular/eliptical gradient?

Try this
Copy the layer and adjust the saturation of the copied layer to lower the
blue component, then apply a layer mask to this layer and try a radial
gradient fill on the mask to mask out the overcorrected centre of the top
layer.

MH



Joal Heagney 09-17-2006 01:48 AM

Re: Scanned Slides: Filtering non-uniform edge discolorations
 
Acecliffy wrote:
> MY SITUATION: I am scanning color slides that are 20 years old. They
> have edge discoloration, meaning that the sides are somewhat darker
> (perhaps blueish) than the center of the slide. This is not a problem
> with my slide scanner; rather, it is inherent in the slides. I don't
> know why they have this problem, since I am doing this job for my major
> professor.
>
> So... here is an example of what I am talking aoubt. There is a link
> to a sample image here:
> http://web.ics.purdue.edu/~racz/images/Image012.jpg
>
> The concrete on the left should have roughly the same color as the
> concrete in the center, but it has a blue tint (I believe, maybe it is
> a mixture).
>
> MY QUESTION: Is there a filter to adjust/perform color corrections for
> non-uniformity such as this, where a hue/saturation/balance is
> non-uniform across the image? It may be a linear gradient, or perhaps
> even a circular/eliptical gradient?
>
> Thanks in advance.
>


The problem here is that you need to remove the shadow on the edges,
without effecting the rest of the image's structure. We need a layer
that represents the low-frequency hue/saturation/value information of
the image.

Here is my hack.

1. Duplicate the layer.
2. Hit the duplicate layer with a large Gaussian Blur. I chose a radius
of 300, as your image was 600 pixels tall. This will wipe out all higher
frequency structure, leaving a layer that only contains the non-uniform
hue/saturation/balance information.
3. I then set the Mode of the top layer to Grain Extract.

This results in an image of even hue and value. However the image does
seem to have become somewhat desaturated, and increased brightness. This
could be fixed by:
4. Merging the visible layers, and applying Colour/Contrast, Levels or
Hue/Saturation adjustments.
5. Desaturating the top layer before you merge the visible layers,
except that this doesn't get rid of the blueness in the concrete, and
still results in an increase in overall brightness.

A final option would be to decrease the brightness of the image BEFORE
applying steps 1/2/3, or adjust the top layer's brightness/contrast
after step 3 but before step 4.

Hope this helps?

Joal Heagney


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