dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 422

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

B.1.12
The two-dimensional FIR uses a 3x3 coefficient mask as shown in Figure B-9.
The image is an array of 128 pixels x 128 pixels. To provide boundary conditions for the FIR filtering, the
image is surrounded by a set of zeros such that the image is actually stored as a 130x130 array (see
Figure B-10).
The image (with boundary) is stored in row-major storage. The first element of the array image is
image(1,1) followed by image(1,2). The last element of the first row is image(1,130) followed by the
beginning of the next column image(2,1). These are stored sequentially in the array Image (“im” on
instruction comment) in data memory. For example:
See Table B-2 for the definitions of R0, R2, and R3.
Although many other implementations are possible, this is a realistic type of image environment where the
actual size of the image may not be an exact power of two. Other possibilities include storing a 128x128
image but computing only a 127x127 result, computing a 128x128 result without boundary conditions but
throwing away the pixels on the border, and so on.
B-26
•
•
•
Image(1,1) maps to index 0.
Image(1,130) maps to index 129.
Image(2,1) maps to index 130.
R0
R2
R3
N Point 3x3 2-D FIR Convolution
Variable
image(n,m)
image(n+130,m)
image(n+2*130,m)
output image
FIR coefficients
Figure B-10. Image Stored as 130x130 Array
Figure B-9. 3x3 Coefficient Mask
Table B-2. Variable Descriptions
0
0
0
0
DSP56800 Family Manual
Image
Area
c11
c21
c31
0
0
image(n,m+1)
image(n+130,m+1)
image(n+2*130,m+1)
130
c12
c22
c32
128
Description
c13
c23
c33
0
0
0
0
130
image(n+2*130,m+2)
image(n,m+2)
image(n+130,m+2)
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AA0087
AA0088