[rbrande]

I have an ATI All-in-Wonder 128 Pro video card (and plan to buy the Radeon 7500).


In the color properties for the card, I can perform color curve adjustments of R,G,B with the mouse. I need more precise control, and wonder if the curve color values are stored in a file that can be edited?

 

[Mark Hunter]

Hi RBrande,


Yes, you have fine programmatic control of each color across the entire scale. See the Win32 API SetGammaRamp for details.


Unfortunately, there is no way that I have been able to find to set the gamma ramp for a DirectX surface of another application (like would be the case with WinDVD, PowerDVD or TheaterTek).


You can calibrate your Windows Desktop so that it's perfect, but you can't get your hands on the stuff that really matters (the video surfaces).


Mark

 

[rbrande]

Hi Mark,


The ATI cards allows setting of the Desktop and DVD video gamma ramp. Unfortunately, it only has three points, with the lowest and highest fixed. The "middle" point can be moved anywhere. I am guessing that these values are stored in the registry? I called ATI, but of course they did not know.


Maybe a better solution is to use PowerStrip; It also allows adjustment of the gamma ramp (works both for the desktop and PowerDVD). In addition, it appears that a custom non-linear ramp may easily be created by creating a custom lookup table in the registry (HKLM\\Software\\EnTech\\LUT). Not sure how to create such a table though? Do you have any idea?


Custom gamma would be great to correct Projectors with color problems.......................

 

[Cliff Watson]

â€The ATI cards allows setting of the Desktop and DVD video gamma ramp. Unfortunately, it only has three points, with the lowest and highest fixed. The "middle" point can be moved anywhere. I am guessing that these values are stored in the registry? I called ATI, but of course they did not know.â€


Don’t know about the desktop gamma (never checked), but the overlay has eight gamma correction curves that are fixed at 0.85, 1.0, 1.1, 1.2, 1.45, 1.7, 2.2, and 2.5.

 

[rbrande]

Cliff,

I am sorry, but I think that I was not clear. I am not looking for different gamma values, but how to create a custom gamma curve.


Let's say that I use a gamma curve with G=2.5. Then, for each IRE there is a corresponding intensity, I, for each color, c, where c= Red, Green or Blue.


Thus, normally (assuming no bias):

I(c, IRE)=B*(IRE)^G


For example, for Green (with B=0.001 & G=2.5):


I(Green, IRE)=0, 0.316, 1.789,....., 100

for IRE=0, 10, 20,....., 100


However, I would like a modified relationship I* (at IRE 0 and 10):


I*(Green, IRE)=0.32, 0.35, 1.789,....., 100

for IRE=0, 10, 20,....., 100


Can this be done with PowerStrip by writing values to the registry (HKLM\\Software\\EnTech\\LUT)?

 

[Cliff Watson]

Guess I was not clear either.


The ATI hardware does not support user programmable CLUT for the overlay and has 8 fixed pre-programmed gamma curves that will meet most user’s needs.


You will need a software approach similar to DScaler that can intercept the video and remap the gamma before sending to the video card.

"Can this be done with PowerStrip by writing values to the registry (HKLM\\Software\\EnTech\\LUT)?"


Don't know, never used PowerStrip for that purpose.

 

[rbrande]

Quote:

Originally posted by Cliff Watson You will need a software approach similar to DScaler that can intercept the video and remap the gamma before sending to the video card.

Know of any such software? I have searched on shareware sites, but not found anything.......

 

[Cliff Watson]

Quote:

Originally posted by rbrande Know of any such software? I have searched on shareware sites, but not found anything.......

The only software I've seen is DScaler.

 

[rbrande]

I just checked Dscaler's help file. It appears that a lookup table can be created so that input luminance is mapped to a new output luminance. Perfect except for one crucial problem.....


I need to do this differently for the different colors. It appears that it does it the same for all colors?


A minor "detail" is also that it will not work when playing DVDs. Dscaler only works with capture cards.......