measureTexture

Measure sharpness of texture using Dead Leaves test chart

Since R2024b

Syntax

[sfr,psd,psdRef] = measureTexture(im,roiTexture,roiUniform)

[sfr,psd,psdRef] = measureTexture(im,roiTexture,roiUniform,imRef,roiTextureRef,roiUniformRef)

Description

[sfr,psd,psdRef] = measureTexture(im,roiTexture,roiUniform) calculates the spatial frequency response (SFR) of a Dead Leaves, Spilled Coins, or similar test chart image, im. For these types of test charts, the SFR is a metric for the sharpness of texture. The function also measures the power spectral density (PSD) of the test chart and a simulated reference image, and returns the measurements in psd and psdRef, respectively.

The function simulates a reference image based on regions of interest (ROIs) for texture regions and uniform regions, specified as roiTexture and roiUniform, respectively [1].

[sfr,psd,psdRef] = measureTexture(im,roiTexture,roiUniform,imRef,roiTextureRef,roiUniformRef) calculates the SFR using a real reference image, imRef. The function calculates the PSDs using additional information about ROIs of texture regions and uniform regions within the reference image, specified as roiTextureRef and roiUniformRef, respectively.

Examples

Measure Texture Sharpness of Grayscale Test Chart

Read and display a grayscale test chart image.

im = imread("paintGrayscale.png");
imshow(im)

Select an ROI of the texture region.

roi = drawrectangle(Color="blue");

textureROI = roi.Position;

Select an ROI consisting of uniform background.

roi = drawrectangle(Color="red");

uniformROI = roi.Position;

Measure the sharpness of the texture.

sfr = measureTexture(im,textureROI,uniformROI);

Plot the SFR values as a function of frequency.

plot(sfr,"F","SFR_I")

Input Arguments

im — Test chart image

RGB image | grayscale image

Test chart image, specified as an RGB image or a grayscale image.

roiTexture — Position of texture ROI in test image

1-by-4 numeric vector

Position of a texture ROI in the test image, specified as a 1-by-4 numeric vector. The vector has the form [X Y Width Height], where X and Y are the coordinates of the top-left corner of the ROI. Width and Height are the width and height of the ROI, in pixels.

roiUniform — Position of uniform ROI in test image

1-by-4 numeric vector

Position of a uniform ROI in the test image, specified as a 1-by-4 numeric vector. The vector has the form [X Y Width Height], where X and Y are the coordinates of the top-left corner of the ROI. Width and Height are the width and height of the ROI, in pixels.

imRef — Reference chart image

RGB image | grayscale image

Reference chart image, specified as an RGB image or a grayscale image.

roiTextureRef — Position of texture ROI in reference image

1-by-4 numeric vector

Position of a texture ROI in the reference image, specified as a 1-by-4 numeric vector. The vector has the form [X Y Width Height], where X and Y are the coordinates of the top-left corner of the ROI. Width and Height are the width and height of the ROI, in pixels.

roiUniformRef — Position of uniform ROI in reference image

1-by-4 numeric vector

Position of a uniform ROI in the reference image, specified as a 1-by-4 numeric vector. The vector has the form [X Y Width Height], where X and Y are the coordinates of the top-left corner of the ROI. Width and Height are the width and height of the ROI, in pixels.

Output Arguments

sfr — Spatial frequency response

table

Spatial frequency response of the texture ROI in the test image, returned as a table. The table has f rows, where f is the number of frequency samples.

For color test chart images, the table has five columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
SFR_R	SFR measurement at frequency F of the red channel of the test image, returned as a numeric scalar.
SFR_G	SFR measurement at frequency F of the green channel of the test image, returned as a numeric scalar.
SFR_B	SFR measurement at frequency F of the blue channel of the test image, returned as a numeric scalar.
SFR_Y	SFR measurement at frequency F of the luminance of the test image, returned as a numeric scalar. Luminance (Y) is a linear combination of the red (R), green (G), and blue (B) channels according to: Y = 0.213R + 0.715G + 0.072B

For grayscale test chart images, the table has two columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
SFR_I	SFR measurement at frequency F of the intensity of the test image, returned as a numeric scalar.

psd — PSD of test image

table

PSD of the test image, returned as a table. The table has f rows, where f is the number of frequency samples.

For color test chart images, the table has five columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
PSD_R	PSD measurement at frequency F of the red channel of the test image, returned as a numeric scalar.
PSD_G	PSD measurement at frequency F of the green channel of the test image, returned as a numeric scalar.
PSD_B	PSD measurement at frequency F of the blue channel of the test image, returned as a numeric scalar.
PSD_Y	PSD measurement at frequency F of the luminance of the test image, returned as a numeric scalar. Luminance (Y) is a linear combination of the red (R), green (G), and blue (B) channels according to: Y = 0.213R + 0.715G + 0.072B

For grayscale test chart images, the table has two columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
PSD_I	PSD measurement at frequency F of the intensity of the test image, returned as a numeric scalar.

psdRef — PSD of reference image

table

PSD of the reference image, returned as a table. The table has f rows, where f is the number of frequency samples.

For color test chart images, the table has five columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
PSD_R	PSD measurement at frequency F of the red channel of the reference image, returned as a numeric scalar.
PSD_G	PSD measurement at frequency F of the green channel of the reference image, returned as a numeric scalar.
PSD_B	PSD measurement at frequency F of the blue channel of the reference image, returned as a numeric scalar.
PSD_Y	PSD measurement at frequency F of the luminance of the reference image, returned as a numeric scalar. Luminance (Y) is a linear combination of the red (R), green (G), and blue (B) channels according to: Y = 0.213R + 0.715G + 0.072B

For grayscale test chart images, the table has two columns.

Variable	Description
F	Frequency at which the SFR is sampled, returned as a numeric scalar.
PSD_I	PSD measurement at frequency F of the intensity of the reference image, returned as a numeric scalar.

References

[1] McElvain, Jon, Scott P. Campbell, Jonathan Miller, and Elaine W. Jin. “Texture-Based Measurement of Spatial Frequency Response Using the Dead Leaves Target: Extensions, and Application to Real Camera Systems.” In Digital Photography VI, 7537:115–25. SPIE, 2010. https://doi.org/10.1117/12.838698.

Version History

Introduced in R2024b