Image Processing Toolbox™

makecform - Create color transformation structure

Syntax

C = makecform(type)
C = makecform(type,'WhitePoint', WP)
C = makecform('icc', src_profile, dest_profile)
C = makecform('icc', src_profile, dest_profile, 'SourceRenderingIntent', src_intent, 'DestRenderingIntent', dest_intent)
C = makecform('clut', profile, LUTtype)
C = makecform('mattrc', MatTrc, 'Direction', direction)
C = makecform('graytrc', profile, 'Direction', direction)
C = makecform('named', profile, space)

Description

C = makecform(type) creates the color transformation structure C that defines the color space conversion specified by type. To perform the transformation, pass the color transformation structure as an argument to the applycform function.

The type argument specifies one of the conversions listed in the following table. makecform supports conversions between members of the family of device-independent color spaces defined by the CIE, Commission Internationale de l'Éclairage (International Commission on Illumination). In addition, makecform also supports conversions to and from the sRGB and CMYK color spaces. For a list of the abbreviations used by the Image Processing Toolbox™ software for each color space, see the Remarks section of this reference page.

C = makecform(type,'WhitePoint', WP) specifies the value of the reference illuminant, known as the white point. type can be either 'xyz2lab' or 'lab2xyz'. WP is a 1-by-3 vector of XYZ values scaled so that Y = 1. The default is the CIE illuminant D50, which is also the default illuminant specified in the International Color Consortium specifications ICC.1:2001-04 and ICC.1:2001-12. Use the whitepoint function to create the WP vector.

C = makecform('icc', src_profile, dest_profile) creates a color transform based on two ICC profiles. src_profile and dest_profile are ICC profile structures returned by iccread.

C = makecform('icc', src_profile, dest_profile, 'SourceRenderingIntent', src_intent, 'DestRenderingIntent', dest_intent) creates a color transform based on two ICC color profiles, src_profile and dest_profile, specifying rendering intent arguments for the source, src_intent, and the destination, dest_intent, profiles.

Rendering intents specify the style of reproduction that should be used when these profiles are combined. For most devices, the range of reproducible colors is much smaller than the range of colors represented by the PCS. Rendering intents define gamut mapping techniques. Possible values for these rendering intents are listed below. Each rendering intent has distinct aesthetic and color-accuracy tradeoffs.

C = makecform('clut', profile, LUTtype) creates the color transformation structure C based on a color lookup table (CLUT) contained in an ICC color profile. profile is an ICC profile structure returned by iccread. LUTtype specifies which clut in the profile structure is to be used. Each LUTtype listed in the table below contains the components of an 8-bit or 16-bit LUTtag that performs a transformation between device colors and PCS colors using a particular rendering. For more information about 'clut' transformations, see Section 6.5.7 of the International Color Consortium specification ICC.1:2001-04 (Version 2) or Section 6.5.9 of ICC.1:2001-12 (Version 4), available at www.color.org.

C = makecform('mattrc', MatTrc, 'Direction', direction) creates the color transformation structure C based on a Matrix/Tone Reproduction Curve (MatTRC) model, contained in an ICC color profile. direction can be either 'forward' or 'inverse' and specifies whether the MatTRC is to be applied in the forward or inverse direction. For more information, see section 6.3.1.2 of the International Color Consortium specification ICC.1:2001-04 or ICC.1:2001-12, available at www.color.org.

C = makecform('graytrc', profile, 'Direction', direction) creates the color transformation structure C that specifies a monochrome transform based on a single-channel Tone Reproduction Curve (GrayTRC) contained in an ICC color profile. direction can be either 'forward' or 'inverse' and specifies whether the grayTRC transform is to be applied in the forward (device to PCS) or inverse (PCS to device) direction.

C = makecform('named', profile, space) creates the color transformation structure C that specifies the transformation from color names to color-space coordinates. profile must be a profile structure for a Named Color profile (with a NamedColor2 field). space is either 'PCS' or 'Device'. The 'PCS' option is always available and will return L*a*b* or XYZ coordinates, depending on the 'ConnectionSpace' field in profile.Header, in 'double' format. The 'Device' option, when active, returns device coordinates, the dimension depending on the 'ColorSpace' field in profile.Header, also in 'double' format.

Remarks

The Image Processing Toolbox software uses the following abbreviations to represent color spaces.

Examples

Convert RGB image to L*a*b*, assuming input image is uint8.

rgb = imread('peppers.png');
cform = makecform('srgb2lab');
lab = applycform(rgb,cform); 

Convert from a non-standard RGB color profile to the device-independent XYZ profile connection space. Note that the ICC input profile must includes a MatTRC value.

InputProfile = iccread('myRGB.icc');
C = makecform('mattrc',InputProfile.MatTRC, ...
              'direction', 'forward');

See Also

applycform, iccread, iccwrite, isicc, lab2double, lab2uint16, lab2uint8, whitepoint, xyz2double, xyz2uint16

For a full list of the toolbox color space conversion functions, see Color Space Conversions.

label2rgb

makeConstrainToRectFcn