Create head phantom image
P = phantom(def, n)
P = phantom(E, n)
[P, E] = phantom(...)
P = phantom(def, n) generates
an image of a head phantom that can be used to test the numerical
other two-dimensional reconstruction algorithms.
a grayscale intensity 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. 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 perception
n is a scalar that specifies the number of
rows and columns in
P. If you omit the argument,
P = phantom(E, n) generates
a user-defined phantom, where each row of the matrix
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.
Additive intensity value of the ellipse
Length of the horizontal semiaxis of the ellipse
Length of the vertical semiaxis of the ellipse
x-coordinate of the center of the ellipse
y-coordinate of the center of the ellipse
Angle (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
to generate the phantom.
All inputs and all outputs must be of class
Create the modified Shepp-Logan head phantom image and display it.
P = phantom('Modified Shepp-Logan',200); imshow(P)
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
A, some pixels can have values outside the range
 Jain, Anil K., Fundamentals of Digital Image Processing, Englewood Cliffs, NJ, Prentice Hall, 1989, p. 439.