Display "Saturation" Effect

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Display "Saturation" Effect

David Webster
All,

I am having a funny problem(?) with some 8-bit imagery whereby bright
pixels get rolled over and displayed as near black or dark. This seems to
happen when I add a value to the pixels to shift their dynamic range. For
example, with the TTTREES2.gif image on the website included below, if I
add 100 to each pixel (using Process/Math/Add ...) in an image to bring
the dynamic range from say 0-133 to 100-233, large sections of higher
values show up as dark, not bright. This doesn't seem to happen with other
images. Can someone tell me what's up?

David Webster
http://www.siggraph.org/s95/S95_V1/COMUNITY/OSIRIS/OSIRIS.HTL
You can save this page as html and get the gifs in a folder.
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Re: Display "Saturation" Effect

karo03
gif images are indexed images. The pixel value is translated via a  
lookup table. You should change the image->type to 8-bit or RGB and  
use than Image->Adjust->Brightness/Contrast for changes.
Regards
Karsten

Am 09.10.2009 um 21:06 schrieb David William Webster:

> All,
>
> I am having a funny problem(?) with some 8-bit imagery whereby bright
> pixels get rolled over and displayed as near black or dark. This  
> seems to
> happen when I add a value to the pixels to shift their dynamic  
> range. For
> example, with the TTTREES2.gif image on the website included below,  
> if I
> add 100 to each pixel (using Process/Math/Add ...) in an image to  
> bring
> the dynamic range from say 0-133 to 100-233, large sections of higher
> values show up as dark, not bright. This doesn't seem to happen with  
> other
> images. Can someone tell me what's up?
>
> David Webster
> http://www.siggraph.org/s95/S95_V1/COMUNITY/OSIRIS/OSIRIS.HTL
> You can save this page as html and get the gifs in a folder.

Karsten
[hidden email]
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Re: Display "Saturation" Effect

David Webster
Thanks! That did it. I'm curious though. Are images from 8-bit gif files
stored internall  as something beside ByteProcessor's.

David Webster

On Fri, Oct 9, 2009 at 1:01 PM, Karsten Rodenacker <[hidden email]>wrote:

> gif images are indexed images. The pixel value is translated via a lookup
> table. You should change the image->type to 8-bit or RGB and use than
> Image->Adjust->Brightness/Contrast for changes.
> Regards
> Karsten
>
> Am 09.10.2009 um 21:06 schrieb David William Webster:
>
>
> All,
>>
>> I am having a funny problem(?) with some 8-bit imagery whereby bright
>> pixels get rolled over and displayed as near black or dark. This seems to
>> happen when I add a value to the pixels to shift their dynamic range. For
>> example, with the TTTREES2.gif image on the website included below, if I
>> add 100 to each pixel (using Process/Math/Add ...) in an image to bring
>> the dynamic range from say 0-133 to 100-233, large sections of higher
>> values show up as dark, not bright. This doesn't seem to happen with other
>> images. Can someone tell me what's up?
>>
>> David Webster
>> http://www.siggraph.org/s95/S95_V1/COMUNITY/OSIRIS/OSIRIS.HTL
>> You can save this page as html and get the gifs in a folder.
>>
>
> Karsten
> [hidden email]
>