mio::Gradient Class Reference

Detailed Description

This converts numeric values into rgb values. The object is initialized with the range that the gradient should cover and the gradient type. Then each numeric value that is given will be converted into rgb values from the selected gradient. Data out of range are converted to either the minimum or the maximum of the gradient. Special pixels should return a=true to indicate transparency (however, pure white is the transparency color, so do not use it in your gradients!).

Some special pixels are recognized:

• IOUtils::nodata returns a transparent pixel
• legend::bg_color returns an almost white pixel
• legend::text_color returns a black pixel

The autoscale is handled both by the object and its caller: if "autoscale==true", the gradient might adjust its control points, for example removing sea and snow lines in the terrain gradient. The min and max values are used to scale the gradient: all values less than min will receive the start color while all values greater than max will receive the end color. Therefore true autoscale is acheived by:

• setting min/max to the data min/max
• passing i_autoscale=true so the gradient might receive some specific adjustments

On the other hand, fixed scale is acheived by:

• setting min/max to fixed values (so the gradient will be rescaled between these fixed boundaries)
• passing i_autoscale=false so the gradient might be able to set so fix points (like sea and snow line)

For some interesting discussion on how to define color gradients, see Bernice E. Rogowitz, Lloyd A. Treinish "Why Should Engineers and Scientists Be Worried About Color?" http://www.research.ibm.com/people/l/lloydt/color/color.HTM

Author

Mathias Bavay

Date

2012-01-06

#include <Graphics.h>

Public Types
enum	Type {   none , terrain , slope , azi ,   heat , freeze , blue_pink , pastel ,   bg_isomorphic , bluewhitered , whitetoblk , blktowhite ,   blue }
	This enum provides names for possible color gradients. More...

Public Member Functions
	Gradient ()
	Default Constructor. This should be followed by a call to set() before calling getColor. More...
	Gradient (const Type &i_type, const double &min_val, const double &max_val, const bool &i_autoscale)
	Constructor. The object will associate to each numeric value RGB values. See class description for more... More...
	Gradient (const Gradient &c)
	~Gradient ()
void	set (const Type &i_type, const double &min_val, const double &max_val, const bool &i_autoscale)
	Setter See class description for more... More...
void	setNrOfLevels (const unsigned char &i_nr_unique_levels)
	Set a reduced number of levels for the gradient The given argument is an upper bound for the number of unique levels in the generated gradient (leading to a reduced number of colors). This is a specially easy and useful way of reducing a file size with no run time overhead (and even a small benefit) and little visible impact if the number of levels/colors remains large enough (say, at least 20-30). This is only applicable to indexed images, that is when getPalette is called an pixels are set using getColor(const double& val, unsigned char& index). More...
void	getColor (const double &val, unsigned char &r, unsigned char &g, unsigned char &b, bool &a) const
	Get RGB values for a given numeric value See class description for more explanations on the implementation/behavior. More...
void	getColor (const double &val, unsigned char &index) const
	Get palette index values for a given numeric value See class description for more explanations on the implementation/behavior. More...
void	getPalette (std::vector< unsigned char > &palette, size_t &nr_colors) const
	Get palette colors for the selected gradient When building an indexed image, one needs to first retrieve the palette using this method. Afterwards, getColor(val, index) will be called for each pixel in order to retrieve its palette index. The returned colors are interlaced (rgb). More...
Gradient &	operator= (const Gradient &source)

Static Public Attributes
static const unsigned char	channel_max_color = 255
	nr of colors per channel of the generated gradients More...

Member Enumeration Documentation

Type

enum mio::Gradient::Type

This enum provides names for possible color gradients.

Enumerator
none	no type selected
terrain	suitable for DEM. if autoscale, then sea and snow line are turned off
slope	suitable to represent slope
azi	suitable to represent slope azimuth. In autoscale, it becomes a two color gradient
heat	the traditional heat gradient (with all its associated shortcomings)
freeze	two, two-color gradients with a sharp transition at 0
blue_pink	blue to pink gradient, isomorphic gradient
pastel	same color scale as "slope" but linear
bg_isomorphic	drak-blue to light-green isomorphic gradient
bluewhitered	blue to white, then white to red
whitetoblk	white to black gradient
blktowhite	black to white gradient
blue	white to slightly violet gradient. This is similar to the one used for the SLF avalanche bulletin

Constructor & Destructor Documentation

Gradient() [1/3]

mio::Gradient::Gradient ( )

inline

Default Constructor. This should be followed by a call to set() before calling getColor.

Gradient() [2/3]

mio::Gradient::Gradient	(	const Type &	i_type,
		const double &	min_val,
		const double &	max_val,
		const bool &	i_autoscale
	)

Constructor. The object will associate to each numeric value RGB values. See class description for more...

Parameters

i_type	set the color gradient to use, from the enum Gradient::Type
min_val	start value of the gradient
max_val	end value of the gradient
i_autoscale	do autoscale for setting the colors?

Gradient() [3/3]

mio::Gradient::Gradient

(

const Gradient &

c

)

~Gradient()

mio::Gradient::~Gradient ( )

inline

Member Function Documentation

getColor() [1/2]

void mio::Gradient::getColor	(	const double &	val,
		unsigned char &	index
	)		const

Get palette index values for a given numeric value See class description for more explanations on the implementation/behavior.

Parameters

val	numerical value to convert
index	palette index for the given value

getColor() [2/2]

void mio::Gradient::getColor	(	const double &	val,
		unsigned char &	r,
		unsigned char &	g,
		unsigned char &	b,
		bool &	a
	)		const

Get RGB values for a given numeric value See class description for more explanations on the implementation/behavior.

Parameters

val	numerical value to convert
r	red (between 0 and 255)
g	green (between 0 and 255)
b	blue (between 0 and 255)
a	transparent pixel?

getPalette()

void mio::Gradient::getPalette	(	std::vector< unsigned char > &	palette,
		size_t &	nr_colors
	)		const

Get palette colors for the selected gradient When building an indexed image, one needs to first retrieve the palette using this method. Afterwards, getColor(val, index) will be called for each pixel in order to retrieve its palette index. The returned colors are interlaced (rgb).

Parameters

palette	interlaced colors
nr_colors	number of colors in the palette

operator=()

Gradient & mio::Gradient::operator=

(

const Gradient &

source

)

set()

void mio::Gradient::set	(	const Type &	i_type,
		const double &	min_val,
		const double &	max_val,
		const bool &	i_autoscale
	)

Setter See class description for more...

Parameters

i_type	set the color gradient to use, from the enum Gradient::Type
min_val	start value of the gradient
max_val	end value of the gradient
i_autoscale	do autoscale for setting the colors?

setNrOfLevels()

void mio::Gradient::setNrOfLevels

(

const unsigned char &

i_nr_unique_levels

)

Set a reduced number of levels for the gradient The given argument is an upper bound for the number of unique levels in the generated gradient (leading to a reduced number of colors). This is a specially easy and useful way of reducing a file size with no run time overhead (and even a small benefit) and little visible impact if the number of levels/colors remains large enough (say, at least 20-30). This is only applicable to indexed images, that is when getPalette is called an pixels are set using getColor(const double& val, unsigned char& index).

Parameters

i_nr_unique_levels

maximum number of unique levels

Member Data Documentation

channel_max_color

const unsigned char mio::Gradient::channel_max_color = 255

static

nr of colors per channel of the generated gradients

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

• Graphics.h
• Graphics.cc