Use JWCompress to create .jpg files using RGB or YUV image data. More...

#include <JWCompress.hpp>

Inheritance diagram for JWCompress:

Collaboration diagram for JWCompress:

Public Member Functions
	JWCompress (void)
	Constructor. More...

virtual	~JWCompress (void)
	Destructor. More...

virtual JWCompress &	compress (void)
	Compress the given data. More...

virtual JWCompress &	compress_yuv422 (const uint8_t *const data, const size_t bytes_per_row)
	Create a JPEG from 16-bit YUYV data (aka YUY2, or YUV 4:2:2 format). More...

virtual JWCompress &	set_size (const size_t width, const size_t height)
	Set the size of the image. More...

virtual JWCompress &	set_colour (const int components=3, const J_COLOR_SPACE colour_space=JCS_RGB)
	Set the number of colour components and the colour space. More...

virtual JWCompress &	set_default_parameters (const J_COLOR_SPACE colour_space=JCS_RGB)
	Set usable default values for most of the optional parameters. More...

virtual JWCompress &	set_quality (const int quality=75, const bool force_baseline=true)
	Constructs JPEG quantization tables appropriate for the indicated quality setting. More...

virtual JWCompress &	optimized_huffman_tables (void)
	Causes the compressor to compute optimal Huffman coding tables for the image. More...

virtual JWCompress &	set_smoothing (const int smoothing=0)
	Determine if smoothing is accessed. Zero turns it off, 100 sets the maximum amount of smoothing. More...

virtual std::string	get_filename (void) const
	The filename used for input (decompress) or output (compress) if set via set_file(). More...


virtual JWCompress &	set_output_file (const std::string &filename)
	Set the output file into which the compressed JPEG image will be stored. More...

virtual JWCompress &	set_output_file (FILE *f)
	Set the output file into which the compressed JPEG image will be stored. More...


virtual JWCompress &	use_arithmetic_coding (void)
	Arithmetic coding will usually result in marginally smaller files, but require more CPU than Huffman coding. More...

virtual JWCompress &	use_huffman_coding (void)
	Arithmetic coding will usually result in marginally smaller files, but require more CPU than Huffman coding. More...


virtual JWCompress &	use_integer_slow_dct (void)
	The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior. More...

virtual JWCompress &	use_integer_fast_dct (void)
	The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior. More...

virtual JWCompress &	use_float_dct (void)
	The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior. More...

Public Attributes
jpeg_compress_struct	cinfo
	IJG's compression structure. More...


jpeg_error_mgr	jerr
	IJG's structures and pointers to those structures used by derived classes. More...

jpeg_error_mgr *	jerr_ptr
	IJG's structures and pointers to those structures used by derived classes. More...

jpeg_compress_struct *	cinfo_ptr
	IJG's structures and pointers to those structures used by derived classes. More...

jpeg_decompress_struct *	dinfo_ptr
	IJG's structures and pointers to those structures used by derived classes. More...

Protected Member Functions

virtual JW &	set_file (const std::string &filename)
	Protected method to set the input or output file. More...

virtual JW &	set_file (FILE *f)

Protected Attributes
std::string	fname
	The filename used for input (decompress) or output (compress) if set via set_file(). More...

FILE *	file
	Input/output file. Used for output when compressing, and input when decompressing. More...

Detailed Description

Use JWCompress to create .jpg files using RGB or YUV image data.

Constructor & Destructor Documentation

◆ JWCompress()

JWCompress::JWCompress ( void )

Constructor.

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◆ ~JWCompress()

JWCompress::~JWCompress ( void )

virtual

Destructor.

Member Function Documentation

◆ compress()

JWCompress & JWCompress::compress ( void )

virtual

Compress the given data.

◆ compress_yuv422()

JWCompress & JWCompress::compress_yuv422	(	const uint8_t *const	data,
		const size_t	bytes_per_row
	)

virtual

Create a JPEG from 16-bit YUYV data (aka YUY2, or YUV 4:2:2 format).

This format is popular with web cams. The output file is closed in this method once the image has been written.

See also: https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/pixfmt-yuyv.html; https://www.fourcc.org/pixel-format/yuv-yuy2/

Exceptions

std::logic_error	if the output file has not been set
std::logic_error	if the image width or height is invalid or has not been set
std::invalid_argument	if the image data pointer is null
std::invalid_argument	if the bytes per row is invalid

Note: JCS_YCbCr in libjpeg needs 24-bit values. This means 8 bits each for Y, Cb, and Cr. This method automatically takes 16-bit YUV 422 values and converts them to full 24-bit values prior to calling libjpeg to do the actual encoding.

Warning: This method automatically calls set_colour() to set the number of components to 3 and the colour space to JCS_YCbCr.

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◆ get_filename()

virtual std::string JW::get_filename ( void ) const

inlinevirtualinherited

The filename used for input (decompress) or output (compress) if set via set_file().

The only way to set the input or output file is to call JWCompress::set_output_file() or JWDecompress::set_input_file().

◆ optimized_huffman_tables()

virtual JWCompress& JWCompress::optimized_huffman_tables ( void )

inlinevirtual

Causes the compressor to compute optimal Huffman coding tables for the image.

This requires an extra pass over the data and therefore costs a good deal of space and time. The default is FALSE, which tells the compressor to use the supplied or default Huffman tables. In most cases optimal tables save only a few percent of file size compared to the default tables.

See also: use_huffman_coding()

◆ set_colour()

JWCompress & JWCompress::set_colour	(	const int	components = `3`,
		const J_COLOR_SPACE	colour_space = `JCS_RGB`
	)

virtual

Set the number of colour components and the colour space.

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◆ set_default_parameters()

JWCompress & JWCompress::set_default_parameters ( const J_COLOR_SPACE colour_space = JCS_RGB )

virtual

Set usable default values for most of the optional parameters.

This sets all JPEG parameters to reasonable defaults, using only the input image's color space. Many applications will only need to use this routine and perhaps set_quality().

Note: This is automatically called by JWCompress::JWCompress().

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◆ set_file() [1/2]

JW & JW::set_file ( const std::string & filename )

protectedvirtualinherited

Protected method to set the input or output file.

Use the equivalent functions in the derived classes instead.

See also: JWCompress::set_output_file(); JWDecompress::set_input_file()

Exceptions

std::runtime_error if the named file cannot be opened

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◆ set_file() [2/2]

JW & JW::set_file ( FILE * f )

protectedvirtualinherited

Exceptions

std::runtime_error if the file pointer is null

◆ set_output_file() [1/2]

virtual JWCompress& JWCompress::set_output_file ( const std::string & filename )

inlinevirtual

Set the output file into which the compressed JPEG image will be stored.

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◆ set_output_file() [2/2]

virtual JWCompress& JWCompress::set_output_file ( FILE * f )

inlinevirtual

Set the output file into which the compressed JPEG image will be stored.

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◆ set_quality()

JWCompress & JWCompress::set_quality	(	const int	quality = `75`,
		const bool	force_baseline = `true`
	)

virtual

Constructs JPEG quantization tables appropriate for the indicated quality setting.

The quality value is expressed on the 0..100 scale recommended by IJG. The exact mapping from quality values to tables may change in future IJG releases as more is learned about DCT quantization. If the force_baseline parameter is TRUE, then the quantization table entries are constrained to the range 1..255 for full JPEG baseline compatibility. In the current implementation, this only makes a difference for quality settings below 25, and it effectively prevents very small/low quality files from being generated. The IJG decoder is capable of reading the non-baseline files generated at low quality settings when force_baseline is FALSE, but other decoders may not be.

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◆ set_size()

JWCompress & JWCompress::set_size	(	const size_t	width,
		const size_t	height
	)

virtual

Set the size of the image.

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◆ set_smoothing()

virtual JWCompress& JWCompress::set_smoothing ( const int smoothing = 0 )

inlinevirtual

Determine if smoothing is accessed. Zero turns it off, 100 sets the maximum amount of smoothing.

◆ use_arithmetic_coding()

virtual JWCompress& JWCompress::use_arithmetic_coding ( void )

inlinevirtual

Arithmetic coding will usually result in marginally smaller files, but require more CPU than Huffman coding.

◆ use_float_dct()

virtual JWCompress& JWCompress::use_float_dct ( void )

inlinevirtual

The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior.

The integer methods should give the same results on all machines. On machines with sufficiently fast FP hardware, the floating-point method may also be the fastest. The IFAST method is considerably less accurate than the other two; its use is not recommended if high quality is a concern.

◆ use_huffman_coding()

virtual JWCompress& JWCompress::use_huffman_coding ( void )

inlinevirtual

Arithmetic coding will usually result in marginally smaller files, but require more CPU than Huffman coding.

◆ use_integer_fast_dct()

virtual JWCompress& JWCompress::use_integer_fast_dct ( void )

inlinevirtual

The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior.

The integer methods should give the same results on all machines. On machines with sufficiently fast FP hardware, the floating-point method may also be the fastest. The IFAST method is considerably less accurate than the other two; its use is not recommended if high quality is a concern.

◆ use_integer_slow_dct()

virtual JWCompress& JWCompress::use_integer_slow_dct ( void )

inlinevirtual

The FLOAT method is very slightly more accurate than the ISLOW method, but may give different results on different machines due to varying roundoff behavior.

The integer methods should give the same results on all machines. On machines with sufficiently fast FP hardware, the floating-point method may also be the fastest. The IFAST method is considerably less accurate than the other two; its use is not recommended if high quality is a concern.

Member Data Documentation

◆ cinfo

jpeg_compress_struct JWCompress::cinfo

IJG's compression structure.

See also: jpeglib.h

◆ cinfo_ptr

jpeg_compress_struct* JW::cinfo_ptr

inherited

IJG's structures and pointers to those structures used by derived classes.

◆ dinfo_ptr

jpeg_decompress_struct* JW::dinfo_ptr

inherited

IJG's structures and pointers to those structures used by derived classes.

◆ file

FILE* JW::file

protectedinherited

Input/output file. Used for output when compressing, and input when decompressing.

◆ fname

std::string JW::fname

protectedinherited

The filename used for input (decompress) or output (compress) if set via set_file().

See also: get_filename()

◆ jerr

jpeg_error_mgr JW::jerr

inherited

IJG's structures and pointers to those structures used by derived classes.

◆ jerr_ptr

jpeg_error_mgr* JW::jerr_ptr

inherited

IJG's structures and pointers to those structures used by derived classes.

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

src/JWCompress.hpp
src/JWCompress.cpp

Public Member Functions

Public Attributes

Protected Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

◆ JWCompress()

◆ ~JWCompress()

Member Function Documentation

◆ compress()

◆ compress_yuv422()

◆ get_filename()

◆ optimized_huffman_tables()

◆ set_colour()

◆ set_default_parameters()

◆ set_file() [1/2]

◆ set_file() [2/2]

◆ set_output_file() [1/2]

◆ set_output_file() [2/2]

◆ set_quality()

◆ set_size()

◆ set_smoothing()

◆ use_arithmetic_coding()

◆ use_float_dct()

◆ use_huffman_coding()

◆ use_integer_fast_dct()

◆ use_integer_slow_dct()

Member Data Documentation

◆ cinfo

◆ cinfo_ptr

◆ dinfo_ptr

◆ file

◆ fname

◆ jerr

◆ jerr_ptr