pgray2bw

Converts gray scale image to black and white image.

Synopsis

pgray2bw [-m mask] [im_in|-] [im_out|-]

Description

pgray2bw is a mean to reduce the gray level range of images down to the 2 colors. It consists of mapping the original grey image into a binary image.

The technique consists in using a grey-level pattern (a dither matrix) image to be compared to the original image. If the pixel is greater than the pixel on the pattern, the output pixel is white (255), otherwise it is black (0).

The 16x16 dither matrix used in this operator is:

{128,	32,	160,	8,	136,	40,	168,	2,	130,	34,	162,	10,	138,	42,	170,	192},
{64,	224,	96,	200,	72,	232,	104,	194,	66,	226,	98,	202,	74,	234,	106,	48},
{176,	16,	144,	56,	184,	24,	152,	50,	178,	18,	146,	58,	186,	26,	154,	240},
{112,	208,	80,	248,	120,	216,	88,	242,	114,	210,	82,	250,	122,	218,	90,	12},
{140,	44,	172,	4,	132,	36,	164,	14,	142,	46,	174,	6,	134,	38,	166,	204},
{76,	236,	108,	196,	68,	228,	100,	206,	78,	238,	110,	198,	70,	230,	102,	60},
{188,	28,	156,	52,	180,	20,	148,	62,	190,	30,	158,	54,	182,	22,	150,	252},
{124,	220,	92,	244,	116,	212,	84,	254,	126,	222,	94,	246,	118,	214,	86,	3},
{131,	35,	163,	11,	139,	43,	171,	1,	129,	33,	161,	9,	137,	41,	169,	195},
{67,	227,	99,	203,	75,	235,	107,	193,	65,	225,	97,	201,	73,	233,	105,	51},
{179,	19,	147,	59,	187,	27,	155,	49,	177,	17,	145,	57,	185,	25,	153,	243},
{115,	211,	83,	251,	123,	219,	91,	241,	113,	209,	81,	249,	121,	217,	89,	15},
{143,	47,	175,	7,	135,	39,	167,	13,	141,	45,	173,	5,	133,	37,	165,	207},
{79,	239,	111,	199,	71,	231,	103,	205,	77,	237,	109,	197,	69,	229,	101,	63},
{191,	31,	159,	55,	183,	23,	151,	61,	189,	29,	157,	53,	181,	21,	149,	254},
{254,	127,	223,	95,	247,	119,	215,	87,	253,	125,	221,	93,	245,	117,	213,	85}};

For each pixel p of the input image:

   if (im_in[p] >= matrix[p.y%16][p.x%16])
      imd[p]=255;
   else
      imd[p]=0;

Inputs

im_in: a 2D image of bytes (Img2duc).

Outputs

im_out: a 2D image of bytes (Img2duc).

Result

Returns SUCCESS or FAILURE.

Examples

Transforms image 'tangram.pan' to black and white image.

   pgray2bw tangram.pan a.pan

C++ prototype

Errc PGray2BW( const Img2duc &im_in, Img2duc &im_out );

Version française

Conversion d'une image de niveaux de gris en une image binaire équivalente.

Author: Régis Clouard