basically a wrapper for Get/SetDeviceGammaRamp

lut.c

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

int main(int argc, char **argv)
{
	if (argc < 2 || argv[1][0] == 'h') {
		printf("usage: %s [arguments]\n"
			"arguments:\n"
			"  c [slope]            reset lut to linear function. (default: 256)\n"
			"                       default windows slope is 256. dispwin -c slope is 257.\n"
			"  g r|g|b|a [num]      get lut value for r/g/b/all for input num. default: all\n"
			"  s r|g|b|a num val    set lut value for r/g/b/all for input num to val.\n"
			"                       allowable ranges: 0 <= num <= 255, 0 <= val <= 65535\n"
			"  r file               set lut from a file formatted like output of %s g a\n"
			"example:\n"
			"  %s g a > mylutfile\n"
			"  *modify mylutfile to whatever*\n"
			"  %s r mylutfile\n",
			argv[0], argv[0], argv[0], argv[0]
			);
		return 0;
	}
	
	WORD vals[3][256];
	double slope = 256.0;
	int col, in;
	int val;
	FILE *lut_file;
	
	HDC hdc = GetDC(NULL);
	
	switch (argv[1][0]) {
	case 'c':
		if (argc > 2) slope = atof(argv[2]);
		if (slope < 128.0 || slope > 512.0) {
			printf("slope must be between 128 and 512...\n");
			return 1;
		}

		for (in = 0; in < 256; in++) {
			val = slope * in;
			val = (val > 65535) ? 65535 : val;
			vals[0][in] = val;
			vals[1][in] = val;
			vals[2][in] = val;
		}

		if (SetDeviceGammaRamp(hdc, vals) == 0) {
			printf("set failed. val must roughly be between num * 257 - 33000 and num * 257 + 33000\n");
			return 0;
		}
		break;
		
	case 'r':
		if (argc < 3) {
			printf("needs file name. run with no arguments for help.\n");
			return 0;
		}
		
		lut_file = fopen(argv[2], "r");
		if (lut_file == NULL) {
			printf("couldn't open file %s", argv[2]);
			return 0;
		}
		
		for (in = 0; in < 256; in++)
			if (fscanf(lut_file, "%hu\t%hu\t%hu", &vals[0][in], &vals[1][in], &vals[2][in]) != 3) {
				printf("wrong file format. format it like output of %s g a", argv[0]);
				return 0;
			}
		
		fclose(lut_file);

		if (SetDeviceGammaRamp(hdc, vals) == 0) {
			printf("set failed. val must roughly be between num * 257 - 33000 and num * 257 + 33000\n");
			return 1;
		}

		break;
	case 'g':
		if (argc < 3) {
			printf("needs color arguments. run with no arguments for help.\n");
			return 0;
		}

		col = argv[2][0];
		col = (col == 'r') ? 0 : (col == 'g') ? 1 : (col == 'b') ? 2 : (col == 'a') ? 3 : -1;
		if (col == -1) {
			printf("invalid color argument. run with no arguments for help.\n");
			return 0;
		}

		if (GetDeviceGammaRamp(hdc, vals) == 0) {
			printf("getting lut failed o.O\n");
			return 0;
		}

		if (argc == 3) { //no num, print everything.
			if (col == 3)
				for (in = 0; in < 256; in++)
					printf("%u\t%u\t%u\n", vals[0][in], vals[1][in], vals[2][in]);
			else
				for (in = 0; in < 256; in++)
					printf("%u\n", vals[col][in]);
			break;
		}
		in = atoi(argv[3]);
		in = (in > 255) ? 255 : (in < 0) ? 0 : in;
		
		if (col == 3)
			printf("%u\t%u\t%u\n", vals[0][in], vals[1][in], vals[2][in]);
		else
			printf("%u\n", vals[col][in]);
		break;
		
	case 's':
		if (argc < 5) {
			printf("needs more arguments. run with no arguments for help.\n");
			return 0;
		}
		
		col = argv[2][0];
		col = (col == 'r') ? 0 : (col == 'g') ? 1 : (col == 'b') ? 2 : (col == 'a') ? 3 : -1;
		if (col == -1) {
			printf("invalid color argument. run with no arguments for help.\n");
			return 0;
		}
		
		in = atoi(argv[3]);
		in = (in > 255) ? 255 : (in < 0) ? 0 : in;
		
		val = atoi(argv[4]);
		val = (val > 65535) ? 65535 : (val < 0) ? 0 : val;
		
		if (GetDeviceGammaRamp(hdc, vals) == 0) {
			printf("getting lut failed o.O\n");
			return 1;
		}
		
		if (col == 3) {
			vals[0][in] = val;
			vals[1][in] = val;
			vals[2][in] = val;
		} else
			vals[col][in] = val;
			
		if (SetDeviceGammaRamp(hdc, vals) == 0) {
			printf("set failed. val must roughly be between num * 257 - 33000 and num * 257 + 33000\n");
			return 1;
		}
		break;

	default:
		printf("invalid argument. run with no arguments for help.\n");
		return 0;
	}

	return 0;
}

Makefile

all:
	gcc lut.c -mconsole -mwindows -o lut