IODCIELabUtil Class Reference

Class supporting color space conversions from and to CIELab. More...

Static Public Member Functions
static void	dicomLab2RGB (double &R, double &G, double &B, double LDicom, double aDicom, double bDicom)
	Convert CIELab color representation as found in DICOM to sRGB value representation.
static void	dicomLab2RGB (Uint8 &R, Uint8 &G, Uint8 &B, Uint16 LDicom, Uint16 aDicom, Uint16 bDicom)
	Convert CIELab color representation as found in DICOM to 8 bit sRGB value representation.
static void	rgb2DicomLab (double &LDicom, double &aDicom, double &bDicom, double R, double G, double B)
	Convert sRGB color representation to CIELab color representation as found in DICOM.
static void	rgb2DicomLab (Uint16 &LDicom, Uint16 &aDicom, Uint16 &bDicom, Uint8 R, Uint8 G, Uint8 B)
	Convert 8 bit sRGB color representation to CIELab color representation as found in DICOM.
static void	dicomlab2Lab (double &L, double &a, double &b, double LDicom, double aDicom, double bDicom)
	Convert CIELab color representation as found in DICOM to CIELab representation.
static void	lab2DicomLab (double &LDicom, double &aDicom, double &bDicom, double L, double a, double b)
	Convert CIELab color representation to CIELab color representation found in DICOM.
static void	rgb2Lab (double &L, double &a, double &b, double R, double G, double B)
	Convert sRGB color representation to CIELab representation (relative to the D50 white point, i.e.
static void	rgb2Xyz (double &X, double &Y, double &Z, double R, double G, double B)
	Convert sRGB color representation to CIE XYZ representation relative to the D50 white point (ICC PCS XYZ), i.e.
static void	xyz2Lab (double &L, double &a, double &b, double X, double Y, double Z)
	Convert CIE XYZ color representation (relative to D50) to CIELab representation (relative to D50).
static void	lab2Rgb (double &R, double &G, double &B, double L, double a, double b)
	Convert CIELab color representation (relative to D50) to sRGB representation.
static void	lab2Xyz (double &X, double &Y, double &Z, double L, double a, double b)
	Convert CIELab color representation (relative to D50) to CIE XYZ representation (relative to D50).
static void	xyz2Rgb (double &R, double &G, double &B, double X, double Y, double Z)
	Convert CIE XYZ color representation (relative to D50, ICC PCS XYZ) to sRGB representation, i.e.

Static Public Attributes
static const double	D50_WHITEPOINT_X
	D50 white point X component (ICC PCS illuminant, CIELab reference white).
static const double	D50_WHITEPOINT_Y
	D50 white point Y component (ICC PCS illuminant, CIELab reference white).
static const double	D50_WHITEPOINT_Z
	D50 white point Z component (ICC PCS illuminant, CIELab reference white).
static const double	D65_WHITEPOINT_X
	D65 white point X component (native white point of sRGB).
static const double	D65_WHITEPOINT_Y
	D65 white point Y component (native white point of sRGB).
static const double	D65_WHITEPOINT_Z
	D65 white point Z component (native white point of sRGB).

Static Protected Member Functions
static double	gammaCorrection (double n)
	Perform sRGB gamma encoding, transforms linear R to R'.
static double	invGammaCorrection (double n)
	Perform inverse sRGB gamma encoding, transforms R' to linear R.
static double	labf (double n)
	CIE L*a*b* f function (used to convert XYZ to L*a*b*).
static double	labfInv (double n)
	CIE L*a*b* inverse f function.
static double	clamp01 (double n)
	Clamp a value to the range 0 <= value <= 1.
static double	roundClamp (double n, double max)
	Round a value to the nearest integer and clamp it to the range 0 <= value <= max.

Detailed Description

Class supporting color space conversions from and to CIELab.

In some IODs DICOM stores CIELab color values (e.g. Recommended Display CIELab Value) which must often be converted to RGB for display or other purposes. This is supported by the functions dicomLab2RGB() and rgb2DicomLab(). The CIELab value range in DICOM is [0,65535] for all three values. The RGB value range in this class is [0,1] (or [0,255] for the 8 bit integer variants). Further functions are available in order to convert between RGB, "normal" CIELab value range as well as CIEXYZ. The class uses double floating point precision for calculations.

DICOM (part 3, C.10.7.1.1) encodes CIELab values in the same way as the ICC Profile Connection Space (PCS), i.e. the CIELab values are relative to the D50 illuminant. The RGB values handled by this class are sRGB values, whose native white point is D65. This class therefore converts sRGB to linear RGB, to CIEXYZ (D65), chromatically adapts the CIEXYZ values to D50 using the linear Bradford transform, and finally computes CIELab relative to the D50 white point (and vice versa). All CIEXYZ values exposed by this class are D50 (PCS) values. The matrices and constants used are those of the CSS Color Module Level 4 sample code (https://www.w3.org/TR/css-color-4/#color-conversion-code), so that results are consistent with other DICOM implementations following the same approach.

Note that up to and including DCMTK 3.7.0 the CIELab values computed by this class were relative to D65, i.e. no chromatic adaptation to the PCS illuminant took place. For neutral (gray) colors the results are the same, for chromatic colors the a* and b* values differ slightly.

Member Function Documentation

clamp01()

double IODCIELabUtil::clamp01 ( double n )

staticprotected

Clamp a value to the range 0 <= value <= 1.

Parameters

n	The value to clamp

Returns

The clamped value

dicomlab2Lab()

void IODCIELabUtil::dicomlab2Lab ( double & L, double & a, double & b, double LDicom, double aDicom, double bDicom )

static

Convert CIELab color representation as found in DICOM to CIELab representation.

See DICOM part 3 for details.

Parameters

L	Output CIELab luminance component with 0 <= L <= 100
a	Output CIELab "a" component (red<->green) with -128 <= a <= 127
b	Output CIELab "b" component (blue<->yellow) with -128 <= b <= 127
LDicom	Input CIELab luminance component with 0 <= L <= 65535 as found in DICOM
aDicom	Input CIELab "a" component (red<->green) with 0 <= a <= 65535 as found in DICOM
bDicom	Input CIELab "b" component (blue<->yellow) with 0 <= b <= 65535 as found in DICOM

dicomLab2RGB() [1/2]

void IODCIELabUtil::dicomLab2RGB ( double & R, double & G, double & B, double LDicom, double aDicom, double bDicom )

static

Convert CIELab color representation as found in DICOM to sRGB value representation.

See DICOM part 3 for details. Colors outside the sRGB gamut are clipped, i.e. the resulting R, G and B values are always within the range 0 <= value <= 1.

Parameters

R	Output sRGB "R" component (red) with 0 <= R <= 1
G	Output sRGB "G" component (green) with 0 <= G <= 1
B	Output sRGB "B" component (blue) with 0 <= B <= 1
LDicom	Input DICOM CIELab luminance component with 0 <= L <= 65535
aDicom	Input DICOM CIELab "a" component (red<->green) with 0 <= a <= 65535
bDicom	Input DICOM CIELab "b" component (blue<->yellow) with 0 <= b <= 65535

dicomLab2RGB() [2/2]

void IODCIELabUtil::dicomLab2RGB ( Uint8 & R, Uint8 & G, Uint8 & B, Uint16 LDicom, Uint16 aDicom, Uint16 bDicom )

static

Convert CIELab color representation as found in DICOM to 8 bit sRGB value representation.

This is a convenience variant of dicomLab2RGB(double&, double&, double&, double, double, double) that rounds the result to the nearest integer and clamps it to the range 0 <= value <= 255.

Parameters

R	Output sRGB "R" component (red) with 0 <= R <= 255
G	Output sRGB "G" component (green) with 0 <= G <= 255
B	Output sRGB "B" component (blue) with 0 <= B <= 255
LDicom	Input DICOM CIELab luminance component with 0 <= L <= 65535
aDicom	Input DICOM CIELab "a" component (red<->green) with 0 <= a <= 65535
bDicom	Input DICOM CIELab "b" component (blue<->yellow) with 0 <= b <= 65535

gammaCorrection()

double IODCIELabUtil::gammaCorrection ( double n )

staticprotected

Perform sRGB gamma encoding, transforms linear R to R'.

Parameters

n	The value to encode, 0 <= n <= 1

Returns

The gamma-encoded value

invGammaCorrection()

double IODCIELabUtil::invGammaCorrection ( double n )

staticprotected

Perform inverse sRGB gamma encoding, transforms R' to linear R.

Parameters

n	The value to decode, 0 <= n <= 1

Returns

The linear value

lab2DicomLab()

void IODCIELabUtil::lab2DicomLab ( double & LDicom, double & aDicom, double & bDicom, double L, double a, double b )

static

Convert CIELab color representation to CIELab color representation found in DICOM.

See DICOM part 3 for details.

Parameters

LDicom	Output CIELab luminance component with 0 <= L <= 65535 as found in DICOM
aDicom	Output CIELab "a" component (red<->green) with 0 <= a <= 65535 as found in DICOM
bDicom	Output CIELab "b" component (blue<->yellow) with 0 <= b <= 65535 as found in DICOM
L	Input CIELab luminance component with 0 <= L <= 100
a	Input CIELab "a" component (red<->green) with -128 <= a <= 127
b	Input CIELab "b" component (blue<->yellow) with -128 <= b <= 127

lab2Rgb()

void IODCIELabUtil::lab2Rgb ( double & R, double & G, double & B, double L, double a, double b )

static

Convert CIELab color representation (relative to D50) to sRGB representation.

Colors outside the sRGB gamut are clipped, i.e. the resulting R, G and B values are always within the range 0 <= value <= 1.

Parameters

R	Output sRGB "R" component (red) with 0 <= R <= 1
G	Output sRGB "G" component (green) with 0 <= G <= 1
B	Output sRGB "B" component (blue) with 0 <= B <= 1
L	Input CIELab luminance component with 0 <= L <= 100
a	Input CIELab "a" component (red<->green) with -128 <= a <= 127
b	Input CIELab "b" component (blue<->yellow) with -128 <= b <= 127

lab2Xyz()

void IODCIELabUtil::lab2Xyz ( double & X, double & Y, double & Z, double L, double a, double b )

static

Convert CIELab color representation (relative to D50) to CIE XYZ representation (relative to D50).

Parameters

X	Output CIE XYZ "X" component with 0 <= X <= D50_WHITEPOINT_X
Y	Output CIE XYZ "Y" component with 0 <= Y <= 1
Z	Output CIE XYZ "Z" component with 0 <= Z <= D50_WHITEPOINT_Z
L	Input CIELab luminance component with 0 <= L <= 100
a	Input CIELab "a" component (red<->green) with -128 <= a <= 127
b	Input CIELab "b" component (blue<->yellow) with -128 <= b <= 127

labf()

double IODCIELabUtil::labf ( double n )

staticprotected

CIE L*a*b* f function (used to convert XYZ to L*a*b*).

Parameters

n	value to convert

Returns

The converted value

labfInv()

double IODCIELabUtil::labfInv ( double n )

staticprotected

CIE L*a*b* inverse f function.

Parameters

n	The value to compute the inverse for

Returns

The resulting inverse

rgb2DicomLab() [1/2]

void IODCIELabUtil::rgb2DicomLab ( double & LDicom, double & aDicom, double & bDicom, double R, double G, double B )

static

Convert sRGB color representation to CIELab color representation as found in DICOM.

See DICOM part 3 for details.

Parameters

LDicom	Output CIELab luminance component with 0 <= L <= 65535 as found in DICOM
aDicom	Output CIELab "a" component (red<->green) with 0 <= a <= 65535 as found in DICOM
bDicom	Output CIELab "b" component (blue<->yellow) with 0 <= b <= 65535 as found in DICOM
R	Input sRGB "R" component (red) with 0 <= R <= 1
G	Input sRGB "G" component (green) with 0 <= G <= 1
B	Input sRGB "B" component (blue) with 0 <= B <= 1

rgb2DicomLab() [2/2]

void IODCIELabUtil::rgb2DicomLab ( Uint16 & LDicom, Uint16 & aDicom, Uint16 & bDicom, Uint8 R, Uint8 G, Uint8 B )

static

Convert 8 bit sRGB color representation to CIELab color representation as found in DICOM.

This is a convenience variant of rgb2DicomLab(double&, double&, double&, double, double, double) that rounds the result to the nearest integer and clamps it to the range 0 <= value <= 65535.

Parameters

LDicom	Output CIELab luminance component with 0 <= L <= 65535 as found in DICOM
aDicom	Output CIELab "a" component (red<->green) with 0 <= a <= 65535 as found in DICOM
bDicom	Output CIELab "b" component (blue<->yellow) with 0 <= b <= 65535 as found in DICOM
R	Input sRGB "R" component (red) with 0 <= R <= 255
G	Input sRGB "G" component (green) with 0 <= G <= 255
B	Input sRGB "B" component (blue) with 0 <= B <= 255

rgb2Lab()

void IODCIELabUtil::rgb2Lab ( double & L, double & a, double & b, double R, double G, double B )

static

Convert sRGB color representation to CIELab representation (relative to the D50 white point, i.e.

ICC PCS CIELab)

Parameters

L	Output CIELab luminance component with 0 <= L <= 100
a	Output CIELab "a" component (red<->green) with -128 <= a <= 127
b	Output CIELab "b" component (blue<->yellow) with -128 <= b <= 127
R	Input sRGB "R" component (red) with 0 <= R <= 1
G	Input sRGB "G" component (green) with 0 <= G <= 1
B	Input sRGB "B" component (blue) with 0 <= B <= 1

rgb2Xyz()

void IODCIELabUtil::rgb2Xyz ( double & X, double & Y, double & Z, double R, double G, double B )

static

Convert sRGB color representation to CIE XYZ representation relative to the D50 white point (ICC PCS XYZ), i.e.

the sRGB values are linearized, converted to CIE XYZ (D65) and then chromatically adapted to D50 using the linear Bradford transform.

Parameters

X	Output CIE XYZ "X" component with 0 <= X <= D50_WHITEPOINT_X
Y	Output CIE XYZ "Y" component with 0 <= Y <= 1
Z	Output CIE XYZ "Z" component with 0 <= Z <= D50_WHITEPOINT_Z
R	Input sRGB "R" component (red) with 0 <= R <= 1
G	Input sRGB "G" component (green) with 0 <= G <= 1
B	Input sRGB "B" component (blue) with 0 <= B <= 1

roundClamp()

double IODCIELabUtil::roundClamp ( double n, double max )

staticprotected

Round a value to the nearest integer and clamp it to the range 0 <= value <= max.

Parameters

n	The value to round and clamp
max	The maximum permitted value

Returns

The rounded and clamped value

xyz2Lab()

void IODCIELabUtil::xyz2Lab ( double & L, double & a, double & b, double X, double Y, double Z )

static

Convert CIE XYZ color representation (relative to D50) to CIELab representation (relative to D50).

Parameters

L	Output CIELab luminance component with 0 <= L <= 100
a	Output CIELab "a" component (red<->green) with -128 <= a <= 127
b	Output CIELab "b" component (blue<->yellow) with -128 <= b <= 127
X	Input CIE XYZ "X" component with 0 <= X <= D50_WHITEPOINT_X
Y	Input CIE XYZ "Y" component with 0 <= Y <= 1
Z	Input CIE XYZ "Z" component with 0 <= Z <= D50_WHITEPOINT_Z

xyz2Rgb()

void IODCIELabUtil::xyz2Rgb ( double & R, double & G, double & B, double X, double Y, double Z )

static

Convert CIE XYZ color representation (relative to D50, ICC PCS XYZ) to sRGB representation, i.e.

the XYZ values are chromatically adapted from D50 to D65 using the linear Bradford transform, converted to linear RGB and finally gamma-encoded. Colors outside the sRGB gamut are clipped, i.e. the resulting R, G and B values are always within the range 0 <= value <= 1.

Parameters

R	Output sRGB "R" component (red) with 0 <= R <= 1
G	Output sRGB "G" component (green) with 0 <= G <= 1
B	Output sRGB "B" component (blue) with 0 <= B <= 1
X	Input CIE XYZ "X" component with 0 <= X <= D50_WHITEPOINT_X
Y	Input CIE XYZ "Y" component with 0 <= Y <= 1
Z	Input CIE XYZ "Z" component with 0 <= Z <= D50_WHITEPOINT_Z

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

• dcmiod/include/dcmtk/dcmiod/cielabutil.h