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/*
* 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 as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
*
* 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;
}
}
}
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