Triton Isis - Manual (Page 196)

June 2004 Isis® Sonar User's Manual, Volume1 182
Filter
(continued) Focus: This is a convolution filter. It uses the kernel of the size that you
specify shown in Table 9-3 and operates on an array of pixels of the
same size in order to determine the value of the center pixel. The dot
product of the two arrays is divided by 8 and subtracted from the
original pixel value. The dot product is the sum of the products of
corresponding elements in the two arrays.
De-speckle (button): Removes “noise” from the image. Noise is defined
as any pixel that exceeds the median kernel value as defined by a
median kernel cell size and a sensitivity value. The median kernel cell
size can have values of 3, 5 or 7. Sensitivity is the number used to
determine how different the center pixel in the image region must be
before the pixel is replaced by the region's median value. During
despeckling, the image is examined in [CellSize] X [CellSize] regions.
The value in the center pixel is compared to the median value for that
region. If the difference between the center value and the median
value exceeds the value specified on the Despeckle bar, the center
pixel is replaced with the median value. Otherwise, the center pixel
keeps its original value. Every pixel in the image is analyzed in this
way.
Enhance Edges Horizontal Top, Vertical Left, Vertical Right, Horizontal Bottom and All
Edges (Sobel) filter. For each of these convolution filters except for the
Sobel filter, the kernels are listed in Table 9-3. (The Sobel filter combines
both horizontal and vertical edge enhancements and therefore does not
appear in Table 9-3.) The dot product of the kernel with the pixel array of
the same size is used for the value of the pixel at the center of the array. If
Show edges only is checked, the pixel at the center of each kernel is
replaced by a zero. This has the effect of reducing the intensity of the
background in the image.
Chapter 9: Using the Tools Menu