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phantom

Create head phantom image

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Syntax

P = phantom(def,n)
P = phantom(E,n)
[P,E] = phantom(___)

Description

P = phantom(def,n) generates an image of a head phantom that can be used to test the numerical accuracy of radon and iradon or other two-dimensional reconstruction algorithms. P is a grayscale image that consists of one large ellipse (representing the brain) containing several smaller ellipses (representing features in the brain). def specifies the type of head phantom to generate, and n specifies the number of rows and columns in the phantom image.

example

P = phantom(E,n) generates a user-defined phantom, where each row of the matrix E specifies an ellipse in the image. E has six columns, with each column containing a different parameter for the ellipses.

[P,E] = phantom(___) returns the matrix E used to generate the phantom.

Examples

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Open Live Script

Create the modified Shepp-Logan head phantom image and display it.

P = phantom('Modified Shepp-Logan',200);
imshow(P)

Figure contains an axes object. The hidden axes object contains an object of type image.

Input Arguments

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Type of head phantom to generate, specified as one of the following.

  • 'Shepp-Logan' — Test image used widely by researchers in tomography

  • 'Modified Shepp-Logan' — Variant of the Shepp-Logan phantom in which the contrast is improved for better visual perception

Data Types: char | string

Number of rows and columns in the phantom image, specified as a positive integer.

Data Types: double

Ellipses that define the phantom, specified as an e-by-6 numeric matrix defining e ellipses. The six columns of E are the ellipse parameters.

Column

Parameter

Meaning

Column 1

A

Additive intensity value of the ellipse

Column 2

a

Length of the horizontal semiaxis of the ellipse

Column 3

b

Length of the vertical semiaxis of the ellipse

Column 4

x0

x-coordinate of the center of the ellipse

Column 5

y0

y-coordinate of the center of the ellipse

Column 6

phi

Angle (in degrees) between the horizontal semiaxis of the ellipse and the x-axis of the image

The domains for the x- and y-axes are [-1,1]. Columns 2 through 5 must be specified in terms of this range.

Data Types: double

Output Arguments

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Phantom image, returned as an n-by-n numeric matrix.

Data Types: double

Tips

For any given pixel in the output image, the pixel's value is equal to the sum of the additive intensity values of all ellipses that the pixel is a part of. If a pixel is not part of any ellipse, its value is 0.

The additive intensity value A for an ellipse can be positive or negative; if it is negative, the ellipse will be darker than the surrounding pixels. Note that, depending on the values of A, some pixels can have values outside the range [0, 1].

References

[1] Jain, Anil K., Fundamentals of Digital Image Processing, Englewood Cliffs, NJ, Prentice Hall, 1989, p. 439.

Version History

Introduced before R2006a

See Also

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