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"Brian Becker" 03-18-2009 01:43 PM

Changing Color Mappings
 
I have been tasked with finding a way to change the color
mappings on a CentOS 5.2 system.* Basically I want to make an image that is
black and white appear in different shades of gray by adjusting the color
mappings.* I need to know the starting point for the color maps however so I
can make the appropriate adjustments.* I have been told this should be some
kind of look up table array of 256x3 elements.** I have searched through the
frame buffer in the kernel and the driver area for the intel frame buffer but
haven't found anything that looks appropriate.* Does this table exist or is the
problem being tackled completely wrong.


*


Any help, ideas, or pointers would be greatly appreciated.


*


Thanks in advance.


Brian







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Kwan Lowe 03-18-2009 05:14 PM

Changing Color Mappings
 
2009/3/18 Brian Becker <bbecker@jaeb.org>:
> I have been tasked with finding a way to change the color mappings on a
> CentOS 5.2 system.* Basically I want to make an image that is black and
> white appear in different shades of gray by adjusting the color mappings.* I
> need to know the starting point for the color maps however so I can make the
> appropriate adjustments.* I have been told this should be some kind of look
> up table array of 256x3 elements.** I have searched through the frame buffer
> in the kernel and the driver area for the intel frame buffer but haven't
> found anything that looks appropriate.* Does this table exist or is the
> problem being tackled completely wrong.

Sounds like you're approaching it incorrectly. I had to do a similar
thing for a class I took some years ago. The goal was to make a viewer
for a fax TIFF image. The approach I used was to break the b/w image
into 4x4 or 8x8 blocks, then count the number of dark pixels and based
on that, assign that to a grayscale level. It worked, but was quite
slow.

ImageMagick has some utilities that do similar things.
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John R Pierce 03-18-2009 06:39 PM

Changing Color Mappings
 
Brian Becker wrote:
>
> I have been tasked with finding a way to change the color mappings on
> a CentOS 5.2 system. Basically I want to make an image that is black
> and white appear in different shades of gray by adjusting the color
> mappings. I need to know the starting point for the color maps
> however so I can make the appropriate adjustments. I have been told
> this should be some kind of look up table array of 256x3 elements. I
> have searched through the frame buffer in the kernel and the driver
> area for the intel frame buffer but haven't found anything that looks
> appropriate. Does this table exist or is the problem being tackled
> completely wrong.
>

just translate your gray scale image on the way to the frame buffer.
messing with the hardware RAMDAC will be extremely hardware specific,
and will affect the entire display, not just your image. modern
computers can completely redraw the screen dozens of times/second,
plenty fast enough for this.




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