Image and Video Processing Libraries in Ptolemy II by ... - CiteSeerX

3.5.2 JAIIDFT
1 1 0
1 0 -1
0 -1 -1
0 1 1
-1 0 1
-1 -1 0
Figure 3.13: Diagonal and Backdiagonal Masks
The Inverse Discrete Fourier Transform [5] transforms an image from the frequency
domain to the spatial domain. Generally, images defined in the frequency
domain contain complex data. The default setting is to attempt to transform
this data into a real image. The JAIIDFT actor can also transform the data into
complex data by switching the dataNature parameter to ComplexToComplex.
For a single-banded image, the Inverse Discrete Fourier Transform is defined to
be:
⎧
⎪⎨
x(n1, n2) =
⎪⎩
1
N1−1
N2−1
N1N2
k1=0 k2=0
X(k1, k2)e j(2π/N1)k1n1 e j(2π/N2)k2n2 , for 0 ≤ n1 ≤ N1 − 1,
0 ≤ n2 ≤ N2 − 1
0, otherwise
The JAIIDFT actor uses a 2 dimensional Inverse Fast Fourier Transform
(IFFT). This means that each dimension is padded with zeros up to the next
power of two, if it is not a power of two itself. Note that the JAIImageToken at
the output of the JAIDFT encapsulates a RenderedOp that contains an image
with a data type of double. The JAIIDFT preserves the data type of the input,
therefore, at the end of a DFT-IDFT chain, the JAIImageToken at the output
encapsulates an image with data type double.
Currently, the only two actors to display images are the ImageDisplay and
MonitorImage actors. When asAWTImage() is called on a JAIImageToken, if
the data type of the encapsulated is anything else but byte, the image will not
render properly.
The JAIDataConvert actor can be used to convert the internal data type to
byte.
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