the code I use to dump ppm because I always forget those P6, P3 etc :p

dump_ppm.c

	{
		unsigned char pix[160 * 160 * 4];
		FILE *fp;
		int i;

		glBindTexture(GL_TEXTURE_2D, gl_tex);
		glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, pix);

		if ((fp = fopen("/tmp/foo.ppm", "wb"))) {
			//fprintf(fp, "P6\n160 160\n255\n");
			fprintf(fp, "P3\n160 160\n255\n");
			for (i = 0; i < 160 * 160; i++) {
#if 0
				fputc(pix[i * 4], fp);
				fputc(pix[i * 4 + 1], fp);
				fputc(pix[i * 4 + 2], fp);
#endif
				fprintf(fp, "%d %d %d\n", (int)pix[i * 4], (int)pix[i * 4 + 1], (int)pix[i * 4 + 2]);
			}
			fclose(fp);
		}
	}