pngpack.c File Reference

Function to pack data with PNG compression. More...

#include <stdlib.h>
#include <math.h>
#include "grib2_int.h"

Go to the source code of this file.

Functions
void	pngpack (float *fld, g2int width, g2int height, g2int *idrstmpl, unsigned char *cpack, g2int *lcpack)
	This subroutine packs up a float data field into PNG image format. More...
static void	pngpack_int (void *fld, int fld_is_double, g2int width, g2int height, g2int *idrstmpl, unsigned char *cpack, g2int *lcpack)
	This internal function packs up float or double data into PNG image format. More...
void	pngpackd (double *fld, g2int width, g2int height, g2int *idrstmpl, unsigned char *cpack, g2int *lcpack)
	This subroutine packs up a double data field into PNG image format. More...

Detailed Description

Function to pack data with PNG compression.

Author

Stephen Gilbert

Date

2003-08-27

Definition in file pngpack.c.

Function Documentation

pngpack()

void pngpack	(	float *	fld,
		g2int	width,
		g2int	height,
		g2int *	idrstmpl,
		unsigned char *	cpack,
		g2int *	lcpack
	)

This subroutine packs up a float data field into PNG image format.

After the data field is scaled, and the reference value is subtracted out, it is treated as a grayscale image and passed to a PNG encoder. It also fills in GRIB2 Data Representation Template 5.41 or 5.40010 with the appropriate values.

Parameters

fld	Pointer to array of float that contains the data values to pack.
width	Number of points in the x direction.
height	Number of points in the y direction.
idrstmpl	Contains the array of values for Data Representation Template 5.41 or 5.40010. 0 Reference value - ignored on input, set by pngpack routine. 1 Binary Scale Factor - used on input. 2 Decimal Scale Factor - used on input. 3 number of bits for each grayscale pixel value - ignored on input. 4 Original field type - currently ignored on input, set = 0 on output. Data values assumed to be reals.
cpack	The packed data field.
lcpack	length of packed field cpack.

Author

Stephen Gilbert

Date

2003-08-27

Author

Ed Hartnett

Definition at line 224 of file pngpack.c.

References pngpack_int().

Referenced by g2_addfield().

pngpack_int()

static void pngpack_int ( void *  fld, int  fld_is_double, g2int  width, g2int  height, g2int *  idrstmpl, unsigned char *  cpack, g2int *  lcpack  )

static

This internal function packs up float or double data into PNG image format.

This is called by pngpack() and pngpackd().

After the data field is scaled, and the reference value is subtracted out, it is treated as a grayscale image and passed to a PNG encoder. It also fills in GRIB2 Data Representation Template 5.41 or 5.40010 with the appropriate values.

Parameters

fld	Pointer to array of float or double that contains the data values to pack.
fld_is_double	If non-zero, then fld is double, otherwise float.
width	Number of points in the x direction.
height	Number of points in the y direction.
idrstmpl	Contains the array of values for Data Representation Template 5.41 or 5.40010. 0 Reference value - ignored on input, set by pngpack routine. 1 Binary Scale Factor - used on input. 2 Decimal Scale Factor - used on input. 3 number of bits for each grayscale pixel value - ignored on input. 4 Original field type - currently ignored on input, set = 0 on output. Data values assumed to be reals.
cpack	The packed data field.
lcpack	length of packed field cpack.

Returns

void

Author

Ed Hartnett

Date

Aug 8, 2022

Definition at line 41 of file pngpack.c.

References ALOG2, enc_png(), int_power(), LOG, mkieee(), and sbits().

Referenced by pngpack(), and pngpackd().

pngpackd()

void pngpackd	(	double *	fld,
		g2int	width,
		g2int	height,
		g2int *	idrstmpl,
		unsigned char *	cpack,
		g2int *	lcpack
	)

This subroutine packs up a double data field into PNG image format.

After the data field is scaled, and the reference value is subtracted out, it is treated as a grayscale image and passed to a PNG encoder. It also fills in GRIB2 Data Representation Template 5.41 or 5.40010 with the appropriate values.

Parameters

fld	Pointer to array of double that contains the data values to pack.
width	Number of points in the x direction.
height	Number of points in the y direction.
idrstmpl	Contains the array of values for Data Representation Template 5.41 or 5.40010. 0 Reference value - ignored on input, set by pngpack routine. 1 Binary Scale Factor - used on input. 2 Decimal Scale Factor - used on input. 3 number of bits for each grayscale pixel value - ignored on input. 4 Original field type - currently ignored on input, set = 0 on output. Data values assumed to be reals.
cpack	The packed data field.
lcpack	length of packed field cpack.

Author

Ed Hartnett

Date

Aug 8, 2022

Definition at line 259 of file pngpack.c.

References pngpack_int().