v4l2_libs/libv4lconvert/sn9c2028-decomp.c

/*
 * sn9c2028-decomp.c
 *
 * Decompression function for the Sonix SN9C2028 dual-mode cameras.
 *
 * Code adapted from libgphoto2/camlibs/sonix, original version of which was
 * Copyright (c) 2005 Theodore Kilgore <kilgota@auburn.edu>
 *
 * History:
 *
 * This decoding algorithm originates from the work of Bertrik Sikken for the
 * SN9C102 cameras. This version is an adaptation of work done by Mattias
 * Krauss for the webcam-osx (macam) project. There, it was further adapted
 * for use with the Vivitar Vivicam 3350B (an SN9C2028 camera) by
 * Harald Ruda <hrx@users.sourceforge.net>. Harald brought to my attention the
 * work done in the macam project and suggested that I use it. One improvement
 * of my own was to notice that the even and odd columns of the image have been
 * reversed by the decompression algorithm, and this needs to be corrected
 * during the decompression.
 *
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License, version 2.1, as published by the Free Software Foundation.
 *
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street - Suite 500,
 * Boston, MA 02111-1307, USA.
 */

#include "libv4lconvert-priv.h"

/* Four defines for bitstream operations, used in the decode function */

#define PEEK_BITS(num, to) { \
	if (bitBufCount < num) { \
		do { \
			bitBuf = (bitBuf << 8) | (*(src++)); \
			bitBufCount += 8; \
		} while (bitBufCount < 24); \
	} \
	to = bitBuf >> (bitBufCount - num); \
}

/*
 * PEEK_BITS puts the next <num> bits into the low bits of <to>.
 * when the buffer is empty, it is completely refilled.
 * This strategy tries to reduce memory access. Note that the high bits
 * are NOT set to zero!
 */

#define EAT_BITS(num) { bitBufCount -= num; bits_eaten += num; }

/*
 * EAT_BITS consumes <num> bits (PEEK_BITS does not consume anything,
 * it just peeks)
 */

#define PARSE_PIXEL(val) {\
	PEEK_BITS(10, bits);\
	if ((bits & 0x200) == 0) {\
		EAT_BITS(1);\
	} \
	else if ((bits & 0x380) == 0x280) {\
		EAT_BITS(3);\
		val += 3;\
		if (val > 255)\
			val = 255;\
	} \
	else if ((bits & 0x380) == 0x300) {\
		EAT_BITS(3);\
		val -= 3;\
		if (val < 0)\
			val = 0;\
	} \
	else if ((bits & 0x3c0) == 0x200) {\
		EAT_BITS(4);\
		val += 8;\
		if (val > 255)\
			val = 255;\
	} \
	else if ((bits & 0x3c0) == 0x240) {\
		EAT_BITS(4);\
		val -= 8;\
		if (val < 0)\
			val = 0;\
	} \
	else if ((bits & 0x3c0) == 0x3c0) {\
		EAT_BITS(4);\
		val -= 20;\
		if (val < 0)\
			val = 0;\
	} \
	else if ((bits & 0x3e0) == 0x380) {\
		EAT_BITS(5);\
		val += 20;\
		if (val > 255)\
			val = 255;\
	} \
	else {\
		EAT_BITS(10);\
		val = 8 * (bits & 0x1f);\
	} \
}


#define PUT_PIXEL_PAIR {\
	long pp;\
	pp = (c1val << 8) + c2val;\
	*((unsigned short *)(dst + dst_index)) = pp;\
	dst_index += 2;\
}

/* Now the decode function itself */

void v4lconvert_decode_sn9c2028(const unsigned char *src, unsigned char *dst,
		int width, int height)
{
	long dst_index = 0;
	int starting_row = 0;
	unsigned short bits;
	short c1val, c2val;
	int x, y;
	unsigned long bitBuf = 0;
	unsigned long bitBufCount = 0;
	unsigned long bits_eaten = 0;

	src += 12;    /* Remove the header */

	for (y = starting_row; y < height; y++) {
		PEEK_BITS(8, bits);
		EAT_BITS(8);
		c2val = (bits & 0xff);
		PEEK_BITS(8, bits);
		EAT_BITS(8);
		c1val = (bits & 0xff);

		PUT_PIXEL_PAIR;

		for (x = 2; x < width ; x += 2) {
			/* The compression reversed the even and odd columns.*/
			PARSE_PIXEL(c2val);
			PARSE_PIXEL(c1val);
			PUT_PIXEL_PAIR;
		}
	}
}