DiscreteCosineTransform Class Reference

Inheritance diagram for DiscreteCosineTransform:

Collaboration diagram for DiscreteCosineTransform:

Public Member Functions
	DiscreteCosineTransform (const boost::filesystem::path &image_path, int persistence)
void	Encode (const boost::filesystem::path &payload_path)
void	Decode ()
Public Member Functions inherited from Steganography
	Steganography (const boost::filesystem::path &image_path)

Private Member Functions
void	EncodeChunk (const int &start, std::vector< unsigned char >::iterator it, std::vector< unsigned char >::iterator en)
void	EncodeChunkLength (const int &start, const unsigned int &chunk_length)
void	DecodeChunk (const int start, std::vector< unsigned char >::iterator it, std::vector< unsigned char >::iterator en)
unsigned int	DecodeChunkLength (const int &start)
void	SwapCoefficients (cv::Mat *block, const int &value)

Private Attributes
std::vector< cv::Mat >	channels
int	persistence
int	image_capacity

Additional Inherited Members
Protected Member Functions inherited from Steganography
std::vector< unsigned char >	ReadPayload (const boost::filesystem::path &payload_path)
void	WritePayload (const boost::filesystem::path &payload_path, const std::vector< unsigned char > &payload)
template<class T >
void	SetBit (T *target, const int &bit, const int &value)
template<class T >
int	GetBit (const T &target, const int &bit)
Protected Attributes inherited from Steganography
boost::filesystem::path	image_path
cv::Mat	image

Constructor & Destructor Documentation

DiscreteCosineTransform()

DiscreteCosineTransform::DiscreteCosineTransform ( const boost::filesystem::path &  image_path, int  persistence  )

inlineexplicit

Default constructor for the DiscreteCosineTransform class which overrides the default constructor from the Steganography class.

Parameters

image_path	The path to the input carrier image.
persistence	The persistence value for this instance.

Member Function Documentation

Decode()

void DiscreteCosineTransform::Decode ( )

virtual

Decode the payload from the steganographic image by comparing DCT coefficients.

Implements Steganography.

DecodeChunk()

void DiscreteCosineTransform::DecodeChunk ( const int  start, std::vector< unsigned char >::iterator  it, std::vector< unsigned char >::iterator  en  )

private

Attempt to decode a chunk of information from the steganographic image.

Parameters

start	The bit index to start decoding at.
it	An iterator to a start position in the payload_bytes vector.
en	An iterator to an end position in the payload_bytes vector.

Exceptions

DecodeException

Thrown when decoding fails.

DecodeChunkLength()

unsigned int DiscreteCosineTransform::DecodeChunkLength ( const int &  start )

private

Attempt to decode the 32bit integer stating the length of the following chunk.

Parameters

start

The bit index to start decoding at.

Returns

The length of the following chunk.

Exceptions

DecodeException

Thrown when decoding fails.

Encode()

void DiscreteCosineTransform::Encode ( const boost::filesystem::path &  payload_path )

virtual

Encode the payload file into the carrier image by swapping DCT coefficients.

Parameters

payload_path

Path to the file we are encoding.

Exceptions

EncodeException

Thrown when encoding fails.

Implements Steganography.

EncodeChunk()

void DiscreteCosineTransform::EncodeChunk ( const int &  start, std::vector< unsigned char >::iterator  it, std::vector< unsigned char >::iterator  en  )

private

Encode a chunk of information into the carrier image.

Before encoding a chunk of information you "should" first encode its length using the EncodeChunkLength function.

Parameters

start	The bit index to start encoding at.
it	The position in the chunk of information to start encoding.
en	The position in the chunk of information to stop encoding.

EncodeChunkLength()

void DiscreteCosineTransform::EncodeChunkLength ( const int &  start, const unsigned int &  chunk_length  )

private

Encode a 32bit integer stating the length of the following chunk into the carrier image.

Parameters

start	The bit index to start encoding at.
chunk_length	The length of the next chunk in bytes.

SwapCoefficients()

void DiscreteCosineTransform::SwapCoefficients ( cv::Mat *  block, const int &  value  )

private

Swap two DCT coefficients.

Swap two DCT coefficients and apply a persistence value to ensure that the data survives the compression process.

Parameters

block	A pointer to the block which is currently be operated on.
value	The value which is being stored, will be 0 or 1.

Member Data Documentation

persistence

DiscreteCosineTransform::persistence

private

Value which will be applied during the DCT coefficient swapping. Higher values ensure that the data persists, however, cause more visual degradation.

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The documentation for this class was generated from the following files:

• include/discrete_cosine_transform.hpp
• src/discrete_cosine_transform.cpp