Gamma Table Calculator adapted from adafruit/RGB-matrix-Panel

gamma.c

// THIS IS NOT ARDUINO CODE -- DON'T INCLUDE IN YOUR SKETCH.  It's a
// command-line tool that outputs a gamma correction table to stdout;
// redirect or copy and paste the results into header file for the
// RGBmatrixPanel library code.
//
// Optional 2 parameters:
// - bit depth (default=4, for 16 output levels).
// - tableSize (default=256 for gamma_table[256])
//
// typical usage:
// gcc -o gamma gamma.c
// ./gamma 4 256

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#define GAMMA 2.5

int planes = 4;
int tableSize = 256;

int main(int argc, char *argv[])
{
	int i, maxval, hexWidth;

	if(argc > 1) planes = atoi(argv[1]);

	if(argc > 2) tableSize = atoi(argv[2]);

	maxval = (1 << planes) - 1;

	int tempVal = maxval;
	hexWidth = 0;
	while(tempVal) {
		hexWidth++;
		tempVal /= 0x10;
	}

	(void)printf(
	  "#ifndef _GAMMA_H_\n"
	  "#define _GAMMA_H_\n\n"
	  "#include <avr/pgmspace.h>\n\n"
	  "static const uint8_t PROGMEM gamma_table[] = {\n  ");

	for(i=0; i<tableSize; i++) {
		(void)printf("0x%0*x",hexWidth,(int)(pow((float)i / (float)tableSize, GAMMA) *
		  (float)maxval + 0.5));
		if(i < tableSize-1) (void)printf(((i & 7) == 7) ? ",\n  " : ",");
	}

	(void)puts(
	  "\n};\n\n"
	  "#endif // _GAMMA_H_");

	return 0;
}

Originally from https://github.com/adafruit/RGB-matrix-Panel/blob/master/extras/gamma.c

Added ability to pass in tableSize parameter, set leading zeros for hex digit based on maxval