VIPS Reference Manual: colour

colour

colour — colour operators

Stability Level

Stable, unless otherwise indicated

Functions

#define	VIPS_D93_X0
#define	VIPS_D93_Y0
#define	VIPS_D93_Z0
#define	VIPS_D75_X0
#define	VIPS_D75_Y0
#define	VIPS_D75_Z0
#define	VIPS_D65_X0
#define	VIPS_D65_Y0
#define	VIPS_D65_Z0
#define	VIPS_D55_X0
#define	VIPS_D55_Y0
#define	VIPS_D55_Z0
#define	VIPS_D50_X0
#define	VIPS_D50_Y0
#define	VIPS_D50_Z0
#define	VIPS_A_X0
#define	VIPS_A_Y0
#define	VIPS_A_Z0
#define	VIPS_B_X0
#define	VIPS_B_Y0
#define	VIPS_B_Z0
#define	VIPS_C_X0
#define	VIPS_C_Y0
#define	VIPS_C_Z0
#define	VIPS_E_X0
#define	VIPS_E_Y0
#define	VIPS_E_Z0
#define	VIPS_D3250_X0
#define	VIPS_D3250_Y0
#define	VIPS_D3250_Z0
gboolean	vips_colourspace_issupported ()
int	vips_colourspace ()
int	vips_LabQ2sRGB ()
int	vips_rad2float ()
int	vips_float2rad ()
int	vips_LabS2LabQ ()
int	vips_LabQ2LabS ()
int	vips_LabQ2Lab ()
int	vips_Lab2LabQ ()
int	vips_LCh2Lab ()
int	vips_Lab2LCh ()
int	vips_Yxy2Lab ()
int	vips_CMC2XYZ ()
int	vips_Lab2XYZ ()
int	vips_XYZ2Lab ()
int	vips_XYZ2scRGB ()
int	vips_scRGB2sRGB ()
int	vips_sRGB2scRGB ()
int	vips_scRGB2XYZ ()
int	vips_LCh2CMC ()
int	vips_CMC2LCh ()
int	vips_XYZ2Yxy ()
int	vips_Yxy2XYZ ()
int	vips_LabS2Lab ()
int	vips_Lab2LabS ()
int	vips_icc_present ()
int	vips_icc_transform ()
int	vips_icc_import ()
int	vips_icc_export ()
int	vips_icc_ac2rc ()
int	vips_dE76 ()
int	vips_dE00 ()
int	vips_dECMC ()
void	vips_col_Lab2XYZ ()
void	vips_col_XYZ2Lab ()
double	vips_col_ab2h ()
void	vips_col_ab2Ch ()
void	vips_col_Ch2ab ()
float	vips_col_L2Lcmc ()
float	vips_col_C2Ccmc ()
float	vips_col_Ch2hcmc ()
void	vips_col_make_tables_CMC ()
float	vips_col_Lcmc2L ()
float	vips_col_Ccmc2C ()
float	vips_col_Chcmc2h ()
int	vips_col_sRGB2scRGB_8 ()
int	vips_col_sRGB2scRGB_16 ()
int	vips_col_scRGB2XYZ ()
int	vips_col_XYZ2scRGB ()
int	vips_col_scRGB2sRGB_8 ()
int	vips_col_scRGB2sRGB_16 ()
float	vips_pythagoras ()
float	vips_col_dE00 ()

Types and Values

enum	VipsIntent
enum	VipsPCS

Includes

#include <vips/vips.h>

Description

These operators let you transform coordinates and images between colour spaces, calculate colour differences, and move to and from device spaces.

Radiance images have four 8-bits bands and store 8 bits of R, G and B and another 8 bits of exponent, common to all channels. They are widely used in the HDR imaging community.

The colour functions can be divided into three main groups. First, functions to transform images between the different colour spaces supported by VIPS: RGB, sRGB, XYZ, Yxy, Lab, LabQ, LabS, LCh and CMC). Use vips_colourspace() to move an image to a target colourspace using the best sequence of colour transform operations. Secondly, there are a set of operations for calculating colour difference metrics. Finally, VIPS wraps LittleCMS and uses it to provide a set of operations for reading and writing images with ICC profiles.

This figure shows how the VIPS colour spaces interconvert:

The colour spaces supported by VIPS are:

LabQ This is the principal VIPS colorimetric storage format. LabQ images have four 8-bit bands and store 10 bits of L and 11 bits of a and b. You cannot perform calculations on LabQ images (they are tagged with VIPS_CODING_LABQ), though a few operations such as vips_extract_area() will work directly with them.
LabS This format represents coordinates in CIELAB space as a three-band VIPS_FORMAT_SHORT image, scaled to fit the full range of bits. It is the best format for computation, being relatively compact, quick, and accurate. Colour values expressed in this way are hard to visualise.
Lab Lab colourspace represents CIELAB colour values with a three-band VIPS_FORMAT_FLOAT image. This is the simplest format for general work: adding the constant 50 to the L channel, for example, has the expected result. VIPS uses D65 LAB, but you can use other colour temperatures with a little effort, see vips_XYZ2Lab().
XYZ CIE XYZ colour space represented as a three-band VIPS_FORMAT_FLOAT image.
Yxy CIE Yxy colour space represented as a three-band VIPS_FORMAT_FLOAT image.
RGB / sRGB VIPS converts XYZ to and from sRGB using the usual formula: http://en.wikipedia.org/wiki/SRGB You can also use vips_icc_transform() and friends to go to and from device space with a generic profile.
LCh Like Lab, but rectangular ab coordinates are replaced with polar Ch (Chroma and hue) coordinates. Hue angles are expressed in degrees.
CMC A colour space based on the CMC(1:1) colour difference measurement. This is a highly uniform colour space, much better than CIELAB for expressing small differences. The CMC colourspace is described in "Uniform Colour Space Based on the CMC(l:c) Colour-difference Formula", M R Luo and B Rigg, Journal of the Society of Dyers and Colourists, vol 102, 1986. Distances in this colourspace approximate, within 10% or so, differences in the CMC(l:c) colour difference formula. You can calculate metrics like CMC(2:1) by scaling the spaces before finding differences.

Functions

VIPS_D93_X0

#define VIPS_D93_X0 (89.7400)

Areas under curves for D93, 2 degree observer.

VIPS_D93_Y0

#define VIPS_D93_Y0 (100.0)

VIPS_D93_Z0

#define VIPS_D93_Z0 (130.7700)

VIPS_D75_X0

#define VIPS_D75_X0 (94.9682)

Areas under curves for D75, 2 degree observer.

VIPS_D75_Y0

#define VIPS_D75_Y0 (100.0)

VIPS_D75_Z0

#define VIPS_D75_Z0 (122.5710)

VIPS_D65_X0

#define VIPS_D65_X0 (95.0470)

Areas under curves for D65, 2 degree observer.

VIPS_D65_Y0

#define VIPS_D65_Y0 (100.0)

VIPS_D65_Z0

#define VIPS_D65_Z0 (108.8827)

VIPS_D55_X0

#define VIPS_D55_X0 (95.6831)

Areas under curves for D55, 2 degree observer.

VIPS_D55_Y0

#define VIPS_D55_Y0 (100.0)

VIPS_D55_Z0

#define VIPS_D55_Z0 (92.0871)

VIPS_D50_X0

#define VIPS_D50_X0 (96.4250)

Areas under curves for D50, 2 degree observer.

VIPS_D50_Y0

#define VIPS_D50_Y0 (100.0)

VIPS_D50_Z0

#define VIPS_D50_Z0 (82.4680)

VIPS_A_X0

#define VIPS_A_X0 (109.8503)

Areas under curves for illuminant A (2856K), 2 degree observer.

VIPS_A_Y0

#define VIPS_A_Y0 (100.0)

VIPS_A_Z0

#define VIPS_A_Z0 (35.5849)

VIPS_B_X0

#define VIPS_B_X0 (99.0720)

Areas under curves for illuminant B (4874K), 2 degree observer.

VIPS_B_Y0

#define VIPS_B_Y0 (100.0)

VIPS_B_Z0

#define VIPS_B_Z0 (85.2230)

VIPS_C_X0

#define VIPS_C_X0 (98.0700)

Areas under curves for illuminant C (6774K), 2 degree observer.

VIPS_C_Y0

#define VIPS_C_Y0 (100.0)

VIPS_C_Z0

#define VIPS_C_Z0 (118.2300)

VIPS_E_X0

#define VIPS_E_X0 (100.0)

Areas under curves for equal energy illuminant E.

VIPS_E_Y0

#define VIPS_E_Y0 (100.0)

VIPS_E_Z0

#define VIPS_E_Z0 (100.0)

VIPS_D3250_X0

#define VIPS_D3250_X0 (105.6590)

Areas under curves for black body at 3250K, 2 degree observer.

VIPS_D3250_Y0

#define VIPS_D3250_Y0 (100.0)

VIPS_D3250_Z0

#define VIPS_D3250_Z0 (45.8501)

vips_colourspace_issupported ()

gboolean
vips_colourspace_issupported (const VipsImage *image);

Test if image is in a colourspace that vips_colourspace() can process. For example, VIPS_INTERPRETATION_RGB images are not in a well-defined colourspace, but VIPS_INTERPRETATION_sRGB ones are.

Parameters

image

input image

Returns

TRUE if image is in a supported colourspace.

vips_colourspace ()

int
vips_colourspace (VipsImage *in,
                  VipsImage **out,
                  VipsInterpretation space,
                  ...);

Optional arguments:

source_space : input colour space

This operation looks at the interpretation field of in (or uses source_space , if set) and runs a set of colourspace conversion functions to move it to space .

For example, given an image tagged as VIPS_INTERPRETATION_YXY, running vips_colourspace() with space set to VIPS_INTERPRETATION_LAB will convert with vips_Yxy2XYZ() and vips_XYZ2Lab().

Parameters

in	input image
out	output image
space	convert to this colour space
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_LabQ2sRGB ()

int
vips_LabQ2sRGB (VipsImage *in,
                VipsImage **out,
                ...);

Unpack a LabQ (VIPS_CODING_LABQ) image to a three-band short image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_rad2float ()

int
vips_rad2float (VipsImage *in,
                VipsImage **out,
                ...);

Unpack a RAD (VIPS_CODING_RAD) image to a three-band float image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_float2rad ()

int
vips_float2rad (VipsImage *in,
                VipsImage **out,
                ...);

Convert a three-band float image to Radiance 32-bit packed format.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_LabS2LabQ ()

int
vips_LabS2LabQ (VipsImage *in,
                VipsImage **out,
                ...);

Convert a LabS three-band signed short image to LabQ

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_LabQ2LabS ()

int
vips_LabQ2LabS (VipsImage *in,
                VipsImage **out,
                ...);

Unpack a LabQ (VIPS_CODING_LABQ) image to a three-band short image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_LabQ2Lab ()

int
vips_LabQ2Lab (VipsImage *in,
               VipsImage **out,
               ...);

Unpack a LabQ (VIPS_CODING_LABQ) image to a three-band float image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_Lab2LabQ ()

int
vips_Lab2LabQ (VipsImage *in,
               VipsImage **out,
               ...);

Convert a Lab three-band float image to LabQ (VIPS_CODING_LABQ).

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_LCh2Lab ()

int
vips_LCh2Lab (VipsImage *in,
              VipsImage **out,
              ...);

Turn LCh to Lab.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_Lab2LCh ()

int
vips_Lab2LCh (VipsImage *in,
              VipsImage **out,
              ...);

Turn Lab to LCh.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_Yxy2Lab ()

int
vips_Yxy2Lab (VipsImage *in,
              VipsImage **out,
              ...);

vips_CMC2XYZ ()

int
vips_CMC2XYZ (VipsImage *in,
              VipsImage **out,
              ...);

vips_Lab2XYZ ()

int
vips_Lab2XYZ (VipsImage *in,
              VipsImage **out,
              ...);

optional arguments:

temp : colour temperature

Turn Lab to XYZ. The colour temperature defaults to D65, but can be specified with temp .

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_XYZ2Lab ()

int
vips_XYZ2Lab (VipsImage *in,
              VipsImage **out,
              ...);

optional arguments:

temp : colour temperature

Turn XYZ to Lab, optionally specifying the colour temperature. temp defaults to D65.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_XYZ2scRGB ()

int
vips_XYZ2scRGB (VipsImage *in,
                VipsImage **out,
                ...);

Turn XYZ to scRGB.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_scRGB2sRGB ()

int
vips_scRGB2sRGB (VipsImage *in,
                 VipsImage **out,
                 ...);

Optional arguments:

depth : depth of output image in bits

Convert an scRGB image to sRGB. Set depth to 16 to get 16-bit output.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_sRGB2scRGB ()

int
vips_sRGB2scRGB (VipsImage *in,
                 VipsImage **out,
                 ...);

Convert an sRGB image to scRGB.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_scRGB2XYZ ()

int
vips_scRGB2XYZ (VipsImage *in,
                VipsImage **out,
                ...);

Turn XYZ to scRGB.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_LCh2CMC ()

int
vips_LCh2CMC (VipsImage *in,
              VipsImage **out,
              ...);

Turn LCh to CMC.

The CMC colourspace is described in "Uniform Colour Space Based on the CMC(l:c) Colour-difference Formula", M R Luo and B Rigg, Journal of the Society of Dyers and Colourists, vol 102, 1986. Distances in this colourspace approximate, within 10% or so, differences in the CMC(l:c) colour difference formula.

This operation generates CMC(1:1). For CMC(2:1), halve Lucs and double Cucs.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_CMC2LCh ()

int
vips_CMC2LCh (VipsImage *in,
              VipsImage **out,
              ...);

Turn LCh to CMC.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_XYZ2Yxy ()

int
vips_XYZ2Yxy (VipsImage *in,
              VipsImage **out,
              ...);

Turn XYZ to Yxy.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_Yxy2XYZ ()

int
vips_Yxy2XYZ (VipsImage *in,
              VipsImage **out,
              ...);

Turn XYZ to Yxy.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_LabS2Lab ()

int
vips_LabS2Lab (VipsImage *in,
               VipsImage **out,
               ...);

Convert a LabS three-band signed short image to a three-band float image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_Lab2LabS ()

int
vips_Lab2LabS (VipsImage *in,
               VipsImage **out,
               ...);

Turn Lab to LabS, signed 16-bit int fixed point.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_icc_present ()

int
vips_icc_present (void);

VIPS can optionally be built without the ICC library. Use this function to test for its availability.

Returns

non-zero if the ICC library is present.

vips_icc_transform ()

int
vips_icc_transform (VipsImage *in,
                    VipsImage **out,
                    const char *output_profile,
                    ...);

Optional arguments:

input_profile : get the input profile from here intent : transform with this intent depth : depth of output image in bits embedded : use profile embedded in input image

Transform an image with a pair of ICC profiles. The input image is moved to profile-connection space with the input profile and then to the output space with the output profile.

If embedded is set, the input profile is taken from the input image metadata, if present. If there is no embedded profile, input_profile is used as a fall-back.

If embedded is not set, the input profile is taken from input_profile . If input_profile is not supplied, the metadata profile, if any, is used as a fall-back.

Use vips_icc_import() and vips_icc_export() to do either the first or second half of this operation in isolation.

Parameters

in	input image
out	output image
output_profile	get the output profile from here
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_icc_import ()

int
vips_icc_import (VipsImage *in,
                 VipsImage **out,
                 ...);

Optional arguments:

input_profile : get the input profile from here intent : transform with this intent embedded : use profile embedded in input image pcs : use XYZ or LAB PCS

Import an image from device space to D65 LAB with an ICC profile. If pcs is set to VIPS_PCS_XYZ, use CIE XYZ PCS instead.

If embedded is set, the input profile is taken from the input image metadata. If there is no embedded profile, input_profile_filename is used as a fall-back.

If embedded is not set, the input profile is taken from input_profile . If input_profile is not supplied, the metadata profile, if any, is used as a fall-back.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_icc_export ()

int
vips_icc_export (VipsImage *in,
                 VipsImage **out,
                 ...);

Optional arguments:

intent : transform with this intent depth : depth of output image in bits output_profile : get the output profile from here pcs : use XYZ or LAB PCS

Export an image from D65 LAB to device space with an ICC profile. If pcs is set to VIPS_PCS_XYZ, use CIE XYZ PCS instead. If output_profile is not set, use the embedded profile, if any. If output_profile is set, export with that and attach it to the output image.

Parameters

in	input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error.

vips_icc_ac2rc ()

int
vips_icc_ac2rc (VipsImage *in,
                VipsImage **out,
                const char *profile_filename);

Transform an image from absolute to relative colorimetry using the MediaWhitePoint stored in the ICC profile.

Parameters

in	input image
out	output image
profile_filename	use this profile

Returns

0 on success, -1 on error.

vips_dE76 ()

int
vips_dE76 (VipsImage *left,
           VipsImage *right,
           VipsImage **out,
           ...);

Calculate dE 76.

Parameters

left	first input image
right	second input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_dE00 ()

int
vips_dE00 (VipsImage *left,
           VipsImage *right,
           VipsImage **out,
           ...);

Calculate dE 00.

Parameters

left	first input image
right	second input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_dECMC ()

int
vips_dECMC (VipsImage *left,
            VipsImage *right,
            VipsImage **out,
            ...);

Calculate dE CMC. The input images are transformed to CMC colour space and the euclidean distance between corresponding pixels calculated.

To calculate a colour difference with values for (l:c) other than (1:1), transform the two source images to CMC yourself, scale the channels appropriately, and call this function.

Parameters

left	first input image
right	second input image
out	output image
...	`NULL`-terminated list of optional named arguments

Returns

0 on success, -1 on error

vips_col_Lab2XYZ ()

void
vips_col_Lab2XYZ (float L,
                  float a,
                  float b,
                  float *X,
                  float *Y,
                  float *Z);

Calculate XYZ from Lab, D65.

Parameters

L	Input CIE Lab value
a	Input CIE Lab value
b	Input CIE Lab value
X	Return CIE XYZ colour
Y	Return CIE XYZ colour
Z	Return CIE XYZ colour

vips_col_XYZ2Lab ()

void
vips_col_XYZ2Lab (float X,
                  float Y,
                  float Z,
                  float *L,
                  float *a,
                  float *b);

Calculate XYZ from Lab, D65.

Parameters

X	Input CIE XYZ colour
Y	Input CIE XYZ colour
Z	Input CIE XYZ colour
L	Return CIE Lab value
a	Return CIE Lab value
b	Return CIE Lab value

vips_col_ab2h ()

double
vips_col_ab2h (double a,
               double b);

Parameters

a	CIE a
b	CIE b

Returns

Hue (degrees)

vips_col_ab2Ch ()

void
vips_col_ab2Ch (float a,
                float b,
                float *C,
                float *h);

vips_col_Ch2ab ()

void
vips_col_Ch2ab (float C,
                float h,
                float *a,
                float *b);

Calculate ab from Ch, h in degrees.

Parameters

C	Chroma
h	Hue angle (degrees)
a	return CIE a* value
b	return CIE b* value

vips_col_L2Lcmc ()

float
vips_col_L2Lcmc (float L);

Calculate Lcmc from L.

Parameters

CIE L*

Returns

Lcmc

vips_col_C2Ccmc ()

float
vips_col_C2Ccmc (float C);

Calculate Ccmc from C.

Parameters

Chroma

Returns

Ccmc.

vips_col_Ch2hcmc ()

float
vips_col_Ch2hcmc (float C,
                  float h);

Calculate hcmc from C and h.

Parameters

C	Chroma
h	Hue (degrees)

Returns

hcmc.

vips_col_make_tables_CMC ()

void
vips_col_make_tables_CMC (void);

Make the lookup tables for cmc.

vips_col_Lcmc2L ()

float
vips_col_Lcmc2L (float Lcmc);

Calculate L from Lcmc using a table. Call vips_col_make_tables_CMC() at least once before using this function.

Parameters

Lcmc

L cmc

Returns

vips_col_Ccmc2C ()

float
vips_col_Ccmc2C (float Ccmc);

Calculate C from Ccmc using a table. Call vips_col_make_tables_CMC() at least once before using this function.

Parameters

Ccmc

Returns

vips_col_Chcmc2h ()

float
vips_col_Chcmc2h (float C,
                  float hcmc);

Calculate h from C and hcmc, using a table. Call vips_col_make_tables_CMC() at least once before using this function.

Parameters

C	Chroma
hcmc	Hue cmc (degrees)

Returns

vips_col_sRGB2scRGB_8 ()

int
vips_col_sRGB2scRGB_8 (int r,
                       int g,
                       int b,
                       float *R,
                       float *G,
                       float *B);

vips_col_sRGB2scRGB_16 ()

int
vips_col_sRGB2scRGB_16 (int r,
                        int g,
                        int b,
                        float *R,
                        float *G,
                        float *B);

vips_col_scRGB2XYZ ()

int
vips_col_scRGB2XYZ (float R,
                    float G,
                    float B,
                    float *X,
                    float *Y,
                    float *Z);

vips_col_XYZ2scRGB ()

int
vips_col_XYZ2scRGB (float X,
                    float Y,
                    float Z,
                    float *R,
                    float *G,
                    float *B);

vips_col_scRGB2sRGB_8 ()

int
vips_col_scRGB2sRGB_8 (float R,
                       float G,
                       float B,
                       int *r,
                       int *g,
                       int *b,
                       int *or_ret);

vips_col_scRGB2sRGB_16 ()

int
vips_col_scRGB2sRGB_16 (float R,
                        float G,
                        float B,
                        int *r,
                        int *g,
                        int *b,
                        int *or_ret);

vips_pythagoras ()

float
vips_pythagoras (float L1,
                 float a1,
                 float b1,
                 float L2,
                 float a2,
                 float b2);

Pythagorean distance between two points in colour space. Lab/XYZ/CMC etc.

Parameters

L1	Input coordinate 1
a1	Input coordinate 1
b1	Input coordinate 1
L2	Input coordinate 2
a2	Input coordinate 2
b2	Input coordinate 2

vips_col_dE00 ()

float
vips_col_dE00 (float L1,
               float a1,
               float b1,
               float L2,
               float a2,
               float b2);

CIEDE2000, from:

Luo, Cui, Rigg, "The Development of the CIE 2000 Colour-Difference Formula: CIEDE2000", COLOR research and application, pp 340

Parameters

L1	Input coordinate 1
a1	Input coordinate 1
b1	Input coordinate 1
L2	Input coordinate 2
a2	Input coordinate 2
b2	Input coordinate 2

Returns

CIE dE2000 colour difference.

Types and Values

enum VipsIntent

The rendering intent. VIPS_INTENT_ABSOLUTE is best for scientific work, VIPS_INTENT_RELATIVE is usually best for accurate communication with other imaging libraries.

Members

VIPS_INTENT_PERCEPTUAL	perceptual rendering intent
VIPS_INTENT_RELATIVE	relative colorimetric rendering intent
VIPS_INTENT_SATURATION	saturation rendering intent
VIPS_INTENT_ABSOLUTE	absolute colorimetric rendering intent

enum VipsPCS

Pick a Profile Connection Space for vips_icc_import() and vips_icc_export(). LAB is usually best, XYZ can be more convenient in some cases.

Members

VIPS_PCS_LAB	use CIELAB D65 as the Profile Connection Space
VIPS_PCS_XYZ	use XYZ as the Profile Connection Space
VIPS_PCS_LAST