RM0020 datasheet(41/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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Arguments:

Description:

Computes the vertical sobel filter on MxN input image. The absolute value of vertical

sobel filter result is range limited to 0..255. The output image is of the same size as

input image and has one pixel border that is not computed. The first and the last row

of output image is not changed, the first column is zeroed and the last column will

contain not meaningful results. The last column can be zeroed when

ZERO_LASTCOL is defined to 1 for the penalty of one more instruction inside inner

loop. The ZERO_LASTCOL is a symbol defined in function source file.

Algorithm:

Compute vertical sobel filter, i.e. compute 2-D convolution with the following kernel:

2. Get absolute value of result

3. Range limit to 0..255

Note: The input/output images must be properly aligned in memory as described in

Table 20.

Performance: See Section 7 and Table 51.

Example 20. sobel3x3_vertical

#include "libdsp2.h"

/* #pragma and ALIGN macros used to align to 4 bytes */

#ifdef __ghs__

#pragma alignvar (4)

#endif

ALIGN_DCC(4)

unsigned char a[16*12];

/* #pragma and ALIGN macros used to align to 4 bytes */

#ifdef __ghs__

#pragma alignvar (4)

#endif

ALIGN_DCC(4)

unsigned char b[16*12] ALIGN_MWERKS(4);

unsigned short M, N, shift;

Table 20.

sobel3x3_vertical arguments

a(1)

a and b must be word aligned.

input image of size MxN

b(1)

out

output image of size MxN

number of rows of a and b, must be >= 3

number of columns of a and b, must be multiple of 4, must be >= 8

– 01

– 02

– 01

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