Image

Description

The Image data type stores information about dimensions, pixel format and raw pixel values. The list of possible formats is similar to the one from the OpenCV library – there can be from 1 to 4 channels and 6 possible primitive types:

  • sint8 - integer number from -128 to 127
  • uint8 - integer number from 0 to 255
  • sint16 - integer number from -32768 to 32767
  • uint16 - integer number from 0 to 65535
  • sint32 - integer number from -2147483648 to 2147483647
  • real - real (floating point) number

For maximum flexibility handling of specific color spaces is left to appropriate filters.

A single-channel image.

A 3-channel RGB image.

A 3-channel HSV image displayed as RGB.

Geometrical Coordinates

If w and h are the image dimensions, then all real-valued coordinates within the image are included in the ranges from 0.0 to w and from 0.0 to h (right-open). The top left pixel of the image covers the square area with the top-left corner at (0.0, 0.0) and the bottom-right corner at (w, h). The X axis is directed to the right, the Y axis downwards.

Angles are in degrees – from 0 to 360. For directions, the angle 0 denotes the direction of the X axis, i.e. the direction from left to right. The angles increase in the clock-wise manner.

Memory Representation

When writing user filters you need to know the memory representation of images. The pixel data of an image is stored in a continuous memory buffer of the following structure:

  • First in the buffer comes the upper-left pixel.
  • Then follow the remaining pixels of the first row.
  • Channels are interleaved, i.e. all components of a single pixel are located at neighboring memory addresses.
  • There might be a memory padding at the end of each row (including the last one) to improve memory alignment.
  • The offset of the beginning of the k'th row is equal to 'k * pitch', where 'pitch' is the byte-distance between consecutive rows. Due to row padding this might be different than 'pixel_size * width'.

Remarks

  • A region of interest, if required, is supposed to be provided as a separate object.
  • Maximum image dimensions are 65535 x 65535.

Library Definition

class Image
{
protected:
	int                width;           // number of pixel columns            
	int                height;          // number of pixel rows
	int                pitch;           // byte-distance between consecutive rows
	PlainType::Type    type;            // type of channels
	int                depth;           // number of channels
	atl::Blob          blob;            // the pixel data
	int                pixelSize;       // byte-size of a pixel (computed from 'type' and 'depth')

public:
	/// Constructor used for images, which will be created later, e.g. by 'LoadFromBmp' function
	Image();
	
	/// Constructor used for creating new images
	Image( int width, int height, PlainType::Type type, int depth, atl::Optional< const Region&amp;&> inRoi );
	
	/// Constructor used for creating wrappers on existing data
	Image( int width, int height, int pitch, PlainType::Type type, int depth, void* data );
	
	/// Copying constructor. Performs deep data copy
	Image( const Image& rhs );

	~Image();

	/// Deep data copy
	Image& operator = ( const Image& rhs );

	void                  Reset();

	/// Iff the format is different then recreates the image (pixel data will be own).
	/// Typically used for (re-)creating output images in image processing functions.
	void                  Reset( int width, int height, PlainType::Type type, int depth,
								 atl::Optional< const Region&amp;&> inRoi );
	void                  Reset( const Image& rhs, atl::Optional< const Region&amp;&> inRoi );

	/// Turns the image into a wrapper of external data (pixel data will be NOT own)
	void                  Reset( int width, int height, int pitch, PlainType::Type type, int depth,
								 void* data );

	inline int            Width () const;
	inline int            Height() const;
	inline int            Pitch () const;
	inline int            Area  () const;
	inline Box            Frame() const;

	/// Number of channels (standard RGB images have 3)
	inline int            Depth() const;

	/// Type of channels (standard RGB images have UINT8)
	inline PlainType::Type Type()  const;

	inline PixelFormat    Format() const;

	/// Size of pixels in bytes
	inline int            PixelSize() const;

	/// Direct access to pixel data
	void*                 Data();
	const void*           Data() const;

	/// Returns pointer to pixels memory which since that point will
	/// be owned externally (this image will not delete it in the destructor).
	void*                 Release();

	/// Helper method for range checking
	bool                  HasLocation( int x, int y ) const;
	bool                  HasLocation( Location p ) const;
	bool                  HasPoint( float x, float y ) const;

	int                   PtrToX( const void* ptr ) const;
	int                   PtrToY( const void* ptr ) const;

	/// Direct access to pixel data
	template < typename P&> P*          RowBegin( int i );
	template < typename P&> const P*    RowBegin( int i ) const;
	template < typename P&> P*          RowEnd  ( int i );
	template < typename P&> const P*    RowEnd  ( int i ) const;

	template < typename P&> P*          Ptr( int x, int y );
	template < typename P&> const P*    Ptr( int x, int y ) const;
	template < typename P&> P*          Ptr( const Location& p );
	template < typename P&> const P*    Ptr( const Location& p ) const;

	template < typename P&> P&          Value( int x, int y );
	template < typename P&> const P&    Value( int x, int y ) const;
	template < typename P&> P&          Value( const Location& p );
	template < typename P&> const P&    Value( const Location& p ) const;
}

Methods:

  • int Width() - returns number of pixel columns
  • int Height() - returns number of pixel rows
  • int Pitch() - returns byte-distance between consecutive rows
  • PlainType Type() - returns type of pixel components
  • int Depth() - returns number of channels
  • void* Data() - returns pointer to image data buffer
  • T* RowBegin<T>( int i ) - returns pointer to first element in image row
  • T* RowEnd<T>( int i ) - returns pointer to first after last element in image row
  • T* Ptr<T>( int x, int y ) - returns pointer to element at specified coordinates
  • T& Value<T>( int i ) - allows to access pixel value at specified coordinates

See Also