jpdequan.cpp

超强jpeg解码程序

#include <iostream>
#include "jpdequan.h"
#include "jpegdeco.h"
#include "jpgexcep.h"

using namespace std ;

//
//  Description:
//
//    Class Default Constructor
//
JpegDecoderQuantizationTable::JpegDecoderQuantizationTable ()
{
  table_defined = false ;
  memset (data_values, 0, sizeof (data_values)) ;
  return ;
}

//
//  Description:
//
//    This function reads a quantization table from a JPEG stream.
//
//  Parameters:
//    decoder:  The JPEG decoder that owns the table and the JPEG stream.
//    precision: The quantization table precision
//
void JpegDecoderQuantizationTable::ReadTable (JpegDecoder &decoder,
                                              unsigned int precision)
{
  // B 2.4.1
  // Determine if 16-bit or 8-bit precision is used for the quantization
  // values in the file.
  if (precision == 1)
  {
// Our source code only allows 8-bit data. The standard says
// 16-bit quantization tables are not allowed with 8-bit data.
// The commented code shows how 16-bit tables would be implemented.
//
//    // Read 16-bit values.
//    for (unsigned int ii = 0 ; ii < SampleSize ; ++ ii)
//    {
//      data_values[ii] = decoder.ReadWord () ;
//      if (data_values[ii] == 0)
//        throw EJpegBadData ("Zero value in quantization table") ;
//    }
    throw EJpegBadData ("Only 8-bit Data is Supported") ;
  }
  else if (precision == 0)
  {
    // Read 8-bit values.
    for (unsigned int ii = 0 ; ii < JpegSampleSize ; ++ ii)
    {
      data_values[ii] = decoder.ReadByte () ;
      if (data_values[ii] == 0)
        throw EJpegBadData ("Zero value in quantization table") ;
    }
  }
  else
  {
    throw EJpegBadData ("Invalid Quantization Table Precision") ;
  }

  table_defined = true ;
  return ;
}

//
//  Description:
//
//    This is a debugging function that prints the contents
//    of the quantization table to a stream.
//
//  Parameters:
//
//    strm:  The output stream
//
void JpegDecoderQuantizationTable::Print (std::ostream &strm) const
{
  for (unsigned int ii = 0 ; ii < JpegSampleWidth ; ++ ii)
  {
    strm << endl << "        "  ;
    for (unsigned int jj = 0 ; jj < JpegSampleWidth ; ++ jj)
    {
      strm << dec
           << data_values [ii * JpegSampleWidth + jj]
           << " " ;
    }
  }
  return ;
}