## NAME

         dpc_compress - compresses an image using differential  pulse
         code modulation

## SYNOPSIS

          #include "CVIPimage.h"
          #include "CVIPcompress.h"
          #include <sys/stat.h>

         int dpc_compress(Image *inputImage,  char  *filename,  float
         ratio,  int   bit_length,  int  clipping, int direction, int
         origin)

          <inputImage> - a pointer to an Image structure
          <filename> - pointer to char string containing filename
          <ratio> - the correlation factor
          <bit_length> - number of bits for compression (1 to 8)
          <clipping> - clip to maximum value (1), otherwise 0
          <direction> - scan image horizontally (0) or vertically (1)
          <origin> - use original (1) or reconstructed (0) values

         Image *dpc_decompress(char *filename)

          <filename> - compressed file

## PATH

         $CVIPHOME/COMPRESSION/dpcm.c

## DESCRIPTION

         DPCM is a compression technique  that  uses  the  predictive
         method of differential pulse code modulation. It is based on
         the observation that adjacent pixels are  highly  correlated
         within  real  images,  and it is wasteful to store repeated,
         large values to represent consecutive pixels.  Rather,  DPCM
         stores  an initial value, followed by the difference between
         the initial value and subsequent pixel values. For  example,
         a  line  of  10  white pixels (value = 255) would usually be
         represented in 80 bits(8 bits/pixel X  10  pixels),  whereas
         with  DPCM, only 17 bits are needed: the first pixel needs 8
         bits, but each of the other  pixels  only  requires  1  bit,
         since  the difference between the initial value and the oth-
         ers is zero (255 - 255 = 0).

## TYPES AND CONSTANTS

         none

## RETURN VALUES

         dpc_compress: 0 on success, -1 on failure

         dpc_decompression: an uncompressed image pointer on success,
         a NULL pointer on failure

## HISTORY

         History information recorded: None

## BUGS

         None at this time

## SEE ALSO

         libcompress

## AUTHOR

         Copyright (C) 1996 SIUE - by Scott Umbaugh.