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# phantom() - Image Processing

### Syntax

### Example

### Output / Return Value

### Limitations

### Alternatives / See Also

### Reference

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 intensity image that consists of one large ellipse (representing the brain) containing several smaller ellipses (representing features in the brain).def is a string that specifies the type of head phantom to generate. Valid values are'Shepp-Logan' — Test image used widely by researchers in tomography'Modified Shepp-Logan' (default) — Variant of the Shepp-Logan phantom in which the contrast is improved for better visual perceptionn is a scalar that specifies the number of rows and columns in P. If you omit the argument, n defaults to 256.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. This table describes the columns of the matrix.ColumnParameterMeaning Column 1AAdditive intensity value of the ellipse Column 2aLength of the horizontal semiaxis of the ellipse Column 3bLength of the vertical semiaxis of the ellipse Column 4x0x-coordinate of the center of the ellipse Column 5y0y-coordinate of the center of the ellipse Column 6phiAngle (in degrees) between the horizontal semiaxis of the ellipse and the x-axis of the image For purposes of generating the phantom, the domains for the x- and y-axes span [-1,1]. Columns 2 through 5 must be specified in terms of this range.[P, E] = phantom(...) returns the matrix E used to generate the phantom.

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

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