# Gamma Values for LCD modules

Discussion in 'Electronic Design' started by [email protected], Sep 8, 2006.

1. ### Guest

Hi folks,

How do I calculate the gamma values for LCD module? I am trying to
design a LCD driver board.

Cheers
P

2. ### Guest

What LCD module? A started point is from the LCD spec. Look for
things relate to the LCD illumination charactistic then figure out the
equation... If it's linear then you don't need the gamma correction,
unless your board is designed for optical clinic

cheers,

3. ### Guest

Hi,

I am currently looking at the AUO M190EG01V0. Would this be the
luminance uniformity which is 75 to 80%? The board would also be
designed for smaller modules.

For a FPGA point of view, I guess the functional blocks are as follow;

Analog RGB-> YUV->gamma correction->Hue, saturation, contrast->Digital
RGB (8 bits per color for a 24 bit screen)->LVDS output

For the smaller module would I have to scale it down to 6 bits per
color by rounding the RGB values from 8 bits to 6 bits?? Would tha
affect the gamma correction??

Cheers
P

4. ### Guest

I guess that would affect the gamma calculation as it will be dependent
on the LCD characteristics.

I guess the equation used will be

value_new = pow (value, 1.0 / factor)

where factor will be the gamma value. For the LUT, I will have to
calculate for the 0-255 that is assumming the gamma value is applicable
to red, green and blue instead of separate gamma values for each
colour. The previous design flow would have been wrong as I can't apply
the gamma to the YUV, I would need to convert the YUV to RGB and then
apply the gamma correction using the LUT.

Sorry, I am new to this subject.

A question on the AUO LCD module, from the datasheet I don't seem to be
able to find the gamma value for the monitor. What will be the name
within the datasheet?

The url for the datasheet is
www.bluecubelcd.com/php/content/panels/pdf/19/M190EG01V0.pdf

For the gm2221 chipset, the adaptive color and contrast seem to be

I guess I can always use this chipset instead of the FPGA options but
if I were to scale it down below 18 bit RGB, I will have to round it
down to required RGB and change the bit order for the LVDS
transmission.

Cheers
P

5. ### Guest

Assume your factor > 1 and your value is normalized to range [0, 1],
then I would like to call the above equation "pre-gamma". This
equation is used to compensate the non-linear illumination
characteristic of CRT tubes, it has more the gain in dark area. If
plot the equation, the curve's slope decreasing in x-> direction

If your display device is linear AND the input video has "pre-gamma" in
it then you need an invert function, let call it de-gamma:

value_n =pow(value, factor), where value in range of [0,1]. This plot
has the slope increasing in x-> direction

IMO, if having room in desing then add a LUT for each color, they give
you a whole flexibility.

It doesn't matter when you round from 8 to 6 bit, keep in mind that
the equations apply for normalized signal: value is in range of [0, 1]

cheer,