plotChromaticity

Plot color reproduction on chromaticity diagram

Syntax

plotChromaticity(colorTable)

plotChromaticity

plotChromaticity(___,Name,Value)

Description

plotChromaticity(colorTable) plots on a chromaticity diagram the measured and reference colors, colorTable, for color patch regions of interest (ROIs) in a test chart.

plotChromaticity plots an empty chromaticity diagram.

plotChromaticity(___,Name,Value) adjusts aspects of the display using name-value arguments.

Examples

Display Chromaticity Diagram from Color Accuracy Measurements

This example shows how to display the chromaticity diagram from measurements of color accuracy on an Imatest® eSFR chart.

Read an image of an eSFR chart into the workspace.

I = imread('eSFRTestImage.jpg');

Create an esfrChart object. Display the chart, highlighting the 16 color patches.

chart = esfrChart(I);
displayChart(chart,'displayEdgeROIs',false, ...
    'displayGrayROIs',false,'displayRegistrationPoints',false)

Measure the color in all color patch ROIs.

colorTable = measureColor(chart);

Plot the measured and reference colors in the CIE 1976 L*a*b* color space on a chromaticity diagram. Red circles indicate the reference color and green circles indicate the measured color of each color patch. The chromaticity diagram does not portray the brightness of color.

figure
plotChromaticity(colorTable)

Display Chromaticity Diagram from ColorChecker Chart

Read an image of an X-Rite® ColorChecker® chart into the workspace.

I = imread('colorCheckerTestImage.jpg');

Create a colorChecker object, then display the chart with ROI annotations.

chart = colorChecker(I);
displayChart(chart)

Measure the color in each color patch ROI.

colorTable = measureColor(chart);

Plot the measured and reference colors on a chromaticity diagram.

figure
plotChromaticity(colorTable)

Plot sRGB Primaries and White Point on Chromaticity Diagram

Convert sRGB primary colors to the XYZ color space.

xyz_primaries = rgb2xyz([1 0 0; 0 1 0; 0 0 1]);

Normalize the x and y values of the primary colors.

xyzMag = sum(xyz_primaries,2);
x_primary = xyz_primaries(:,1)./xyzMag;
y_primary = xyz_primaries(:,2)./xyzMag;

Calculate and normalize the D65 white point.

wp = whitepoint('D65');

Normalize the x and y values of the white point.

wpMag = sum(wp,2);
x_whitepoint = wp(:,1)./wpMag;
y_whitepoint = wp(:,2)./wpMag;

Create an empty 2-D chromaticity diagram.

plotChromaticity

Add the (x,y) coordinates of the primaries and white point to the chromaticity diagram.

hold on
scatter(x_whitepoint,y_whitepoint,36,'black')
scatter(x_primary,y_primary,36,'black')
plot([x_primary; x_primary],[y_primary; y_primary],'k')
hold off

Display 3-D Color Solid in u'v'L Color Space

Display a 3-D color solid of the u'v'L color space on an empty chromaticity diagram. Include all u'v'L colors by specifying the brightness threshold as 0.

plotChromaticity("ColorSpace","uv","View",3,"BrightnessThreshold",0)

Input Arguments

colorTable — Color values

color table

Color values in each color patch, specified as an m-by-8 color table, where m is the number of patches. The eight columns represent these variables:

Variable	Description
ROI	Index of the sampled ROI. The value of ROI is an integer in the range [1, 16]. The indices match the ROI numbers displayed by displayChart.
Measured_R	Mean value of red channel pixels in an ROI. Measured_R is a scalar of the same data type as chart.Image, which can be of type single, double, uint8, or uint16.
Measured_G	Mean value of green channel pixels in an ROI. Measured_G is a scalar of the same data type as chart.Image.
Measured_B	Mean value of blue channel pixels in an ROI. Measured_B is a scalar of the same data type as chart.Image.
Reference_L	Reference L* value corresponding to the ROI. Reference_L is a scalar of type double.
Reference_a	Reference a* value corresponding to the ROI. Reference_a is a scalar of type double.
Reference_b	Reference b* value corresponding to the ROI. Reference_b is a scalar of type double.
Delta_E	Euclidean color distance between the measured and reference color values, as outlined in CIE 1976.

Name-Value Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'displayROIIndex',false turns off the display of the ROI indices on the chromaticity diagram.

BrightnessThreshold — Brightness threshold

0.15 (default) | number in the range [0, 1]

Brightness threshold, specified as the comma-separated pair consisting of 'BrightnessThreshold' and a number in the range [0, 1]. The plotChromaticity function does not display color values with a Y or L value (depending on the color space) less than the brightness threshold.

ColorSpace — Color space

'xy' (default) | 'uv'

Color space, specified as the comma-separated pair consisting of 'ColorSpace' and 'xy' to plot in the xyY color space or 'uv' to plot in the u'v'L color space.

Data Types: char | string

displayROIIndex — Display ROI index labels

true or 1 (default) | false or 0

Display ROI index labels, specified as the comma-separated pair consisting of 'displayROIIndex' and a numeric or logical 1 (true) or 0 (false). When displayROIIndex is true, then the plotChromaticity function overlays color patch ROI index labels on the chromaticity diagram. The indices match the ROI numbers displayed by the displayChart function.

Parent — Parent axes

Axes object

Parent axes of the chromaticity diagram, specified as the comma-separated pair consisting of 'Parent' and an Axes object.

View — Dimensionality of chromaticity diagram

2 (default) | 3

Dimensionality of chromaticity diagram, specified as the comma-separated pair consisting of 'View' and 2 for a 2-D projection or 3 for a 3-D color solid.

Tips

• To obtain a color table of the correct format from an esfrChart or colorChecker object, use the measureColor function. You can also create your own color table containing measured and reference colors for an arbitrary number of color ROIs.

• The reference L*a*b* values of a colorTable measured from a colorChecker object are for the "After November 2014" version of the X-Rite^® ColorChecker^® chart. The white point of the reference values is the CIE standard illuminant D50.