Creating and Enriching Graphical User Interfaces - Beginning Java 7 - page 680

0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f

};
Kernel kernel = new Kernel(3, 3, identityKernel);
This kernel describes a 3-by-3 table of values that's applied to each source pixel
anditseightimmediateneighbors.Toinvolvemoreneighbors,increasethesizeofthe
floating-pointarrayandthenumberofrowsandcolumns.Forexample,youcouldcre-
ate a 5-by-5 kernel that involves the source pixel and its 24 immediate neighbors.

Note Although Kernel doesn'trequireodd-numberedwidthandheightarguments,
you might find kernels with an odd number of columns and an odd number of rows
easier to understand.

Aftercreating akernel,youneedtoconsiderwhathappenswhenthekernelisposi-
tionedoverpixelsattheedgesofanimage.Somekernelelementswillhavenocorres-
pondingimagepixels.Forexample,whena3-by-3kernelispositionedwithitscenter
rowoverthetopimagerow,thekernel'stoprowofneighborvalueshasnocorrespond-
ing row of image pixels.
ConvolveOp addresses this situation by declaring EDGE_ZERO_FILL and
EDGE_NO_OP constants.Specifying EDGE_ZERO_FILL causes ConvolveOp toset
edge destination pixels to zero, which is interpreted as black (RGB) or transparent
(ARGB). EDGE_NO_OP causes ConvolveOp to copy source edge pixels to the des-
tination unchanged.
To perform a convolution using this kernel, first instantiate ConvolveOp , as fol-
lows:
BufferedImageOp identityOp = new ConvolveOp(kernel);
RasterOp identityOp = new ConvolveOp(kernel);
The ConvolveOp(Kernel kernel) constructor sets the edge behavior to
EDGE_ZERO_FILL .

Tip Use the ConvolveOp(Kernel kernel, int edgeCondition,
RenderingHints hints) constructortoselecttheedgebehaviorandtherender-
ing hints for controlling the rasterizer.

Continue by invoking a filter() method, as follows:
BufferedImage biResult = identityOp.filter(bi, null);
WriteableRaster

wrResult = iden-

tityOp.filter(bi.getRaster(), null);