BMPファイルから各色を抽出するプログラム

プログラム

bmp_pix_dump.c

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>

int read_start(FILE *fi) {
	int start;

	fseek(fi, 10, SEEK_SET);
	fread(&start, 4, 1, fi);

	return start;
}

int read_width(FILE *fi) {
	int width;

	fseek(fi, 18, SEEK_SET);
	fread(&width, 4, 1, fi);
	
	return width;
}

int read_height(FILE *fi) {
	signed int height;

	fseek(fi, 22, SEEK_SET);
	fread(&height, 4, 1, fi);

	return height;
}

int read_colorbit(FILE *fi) {
	unsigned short bit;

	fseek(fi, 28, SEEK_SET);
	fread(&bit, 2, 1, fi);

	return bit;
}

void read_datablock(FILE *fi, int width, int height, int data_start, int color_bit, int ft) {
	int start, i;
	char pix;
	unsigned char pix_text;

	start = data_start + (color_bit / 8);

	if (ft == 1) {
		printf("P2\n%d %d\n255\n", width, height);
	} else if (ft == 2) {
		printf("P5\n%d %d\n255\n", width, height);
	}

	for (i=0; i<(width*height)*3; i+=3) {
		fseek(fi, i+start, SEEK_SET);
		if (ft == 1) {
			fread(&pix_text, 1, 1, fi);
			printf("%d\n", pix_text);
		} else {
			fread(&pix, 1, 1, fi);
			fwrite(&pix, 1, 1, stdout);
		}
	}
}

int main(int argc, char *argv[]) {
	// ft: bin = 0, text_pgm = 1, bin_pgm = 2
	int i, opt, w, h, data_start, pix_bit, color_bit, ft;
	char *input_file = "", *color = "", *output_file_type = "";
	FILE *fi;

	opterr = 0;

	while ((opt = getopt(argc, argv, "i:c:t:")) != -1) {
		switch (opt) {
			case 'i':
				input_file = optarg;
				break;
			case 'c':
				color = optarg;
				break;
			case 't':
				output_file_type = optarg;
				break;
			default:
				printf("Usage: %s [-i string] [-c {R|G|B}] [-t {bin|text_pgm|bin_pgm}] ...\n", argv[0]);

				return -1;
		}
	}

	fi = fopen(input_file, "r");

	data_start = read_start(fi);

	w = read_width(fi);
	h = abs(read_height(fi));

	pix_bit = read_colorbit(fi);
	if (pix_bit != 24) {
		printf("The input file must be 24-bit color.\n");
		return -1;
	}

	if (strcmp(output_file_type, "bin") == 0) {
		ft = 0;
	} else if (strcmp(output_file_type, "text_pgm") == 0) {
		ft = 1;
	} else if (strcmp(output_file_type, "bin_pgm") == 0) {
		ft = 2;
	} else {
		ft = 0;
	}


	if (strcmp(color, "R") == 0) {
		color_bit = 16;
	} else if (strcmp(color, "G") == 0) {
		color_bit = 8;
	} else if (strcmp(color, "B") == 0) {
		color_bit = 0;
	} else {
		printf("Usage: %s [-i string] [-c {R|G|B}] [-t {bin|text_pgm|bin_pgm}] ...\n", argv[0]);
		return -1;
	}

	read_datablock(fi, w, h, data_start, color_bit, ft);

	return 0;
}

コンパイル

$ cc -o bmp_pix_dump bmp_pix_dump.c

使い方

$ bmp_pix_dump -i image.bmp -c R -t bin_pgm > image.RED.PGM

※ 詳しい使い方はプログラムを読んでください。