Cirrus Logic AN269 - Manual (Page 42)

42 AN269REV1
AN269
7. GRAYSCALE LOOK-UP TABLES
Each of the Red, Green, and Blue outputs from either the color look-up table (LUT) or data directly from memory
can be used as indices into the Grayscale LUT. The purpose of the Grayscale LUTs is to provide a means to dither
the output to low-color and monochrome displays based on X- or Y-coordinate (spatial) or frame number (temporal).
In all, 8 shades (2 of which are always full off and full on) are available for each pixel’s Red, Green, and Blue com-
ponents.
Here are some example grayscale LUTs and an example 4-bit-per-pixel color LUT, in reference code form, as well
as a few simple functions and example function calls (in the “C” language) for programming those tables into mem-
ory. These tables support 0%, 25%, 50%, 75%, and 100% output brightness. Note that some entries are repeated,
and could be used for other settings. Since 3 bits of data are taken as input to the grayscale LUTs, up to 8 shades
may be chosen (2 are always used for full on and full off).
7.1 Grayscale Table Example
const unsigned long rgb_gs_lut_r[32] =
{
// ALL 0 , 25% , 25% , 50% , 50% , 75% , 75% , 100%
0x00070000,0x00071842,0x00071842,0x00075c53,0x00075c53,0x0007e7bd,0x0007e7bd,0x0007ffff,
0x00070000,0x00074218,0x00074218,0x0007a3ac,0x0007a3ac,0x0007bde7,0x0007bde7,0x0007ffff,
0x00070000,0x00078124,0x00078124,0x0007c535,0x0007c535,0x00077edb,0x00077edb,0x0007ffff,
0x00070000,0x00072481,0x00072481,0x00073aca,0x00073aca,0x0007db7e,0x0007db7e,0x0007ffff
};
const unsigned long rgb_gs_lut_g[32] =
{
// ALL 0 , 25% , 25% , 50% , 50% , 75% , 75% , 100%
0x00070000,0x00071842,0x00071842,0x00075c53,0x00075c53,0x0007e7bd,0x0007e7bd,0x0007ffff,
0x00070000,0x00074218,0x00074218,0x0007a3ac,0x0007a3ac,0x0007bde7,0x0007bde7,0x0007ffff,
0x00070000,0x00078124,0x00078124,0x0007c535,0x0007c535,0x00077edb,0x00077edb,0x0007ffff,
0x00070000,0x00072481,0x00072481,0x00073aca,0x00073aca,0x0007db7e,0x0007db7e,0x0007ffff
};
const unsigned long rgb_gs_lut_b[32] =
{
// ALL 0 , 25% , 25% , 50% , 50% , 75% , 75% , 100%
0x00070000,0x00071842,0x00071842,0x00075c53,0x00075c53,0x0007e7bd,0x0007e7bd,0x0007ffff,
0x00070000,0x00074218,0x00074218,0x0007a3ac,0x0007a3ac,0x0007bde7,0x0007bde7,0x0007ffff,
0x00070000,0x00078124,0x00078124,0x0007c535,0x0007c535,0x00077edb,0x00077edb,0x0007ffff,
0x00070000,0x00072481,0x00072481,0x00073aca,0x00073aca,0x0007db7e,0x0007db7e,0x0007ffff
};
void RASTER_FillGreyLUT(INT32 data[], int iLUT)
/* Description:
* Fill the Gray scale LUT.
*
*
* Exception Handling (if any):
* none
*
* Garbage Collection (if any):
* none