FPGA二值图像边界提取算法实现

1 背景知识

图1 二值图像边界提取演示

如图1 所示，图1 a为一幅简单的二值图像，经过边界提取后形成如图1 b 所示的图像，显示出了白色区域的轮廓。

2 边界提取算法

使用黑色提取，背景为白色，‘1’表示白色，‘0’表示黑色。

图2 二值图像边界提取演示

我们使用3x3模板进行边界提取，所以当3x3九个点都是‘1’的时候，输出为‘1’，当九个点都是‘0’的时候，输出为‘1’，其他情况输出均为‘0’。

3FPGA二值图像边界提取算法实现

图2 二值图像膨胀FPGA模块架构

图2中我们使用串口传图传入的是二值图像。

FPGA源码：
/*
Module name: boundary_extraction.v
Description: binary image boundary extraction
*/
`timescale 1ns/1ps


module boundary_extraction(
input clk, //pixel clk
inputrst_n,
input hs_in,
input vs_in,
input [15:0] data_in,
input data_in_en,

output hs_out,
output vs_out,
output reg [15:0] data_out,
output data_out_en
);

wire [15:0] line0;
wire [15:0] line1;
wire [15:0] line2;


reg [15:0] line0_data0;
reg [15:0] line0_data1;
reg [15:0] line0_data2;


reg [15:0] line1_data0;
reg [15:0] line1_data1;
reg [15:0] line1_data2;


reg [15:0] line2_data0;
reg [15:0] line2_data1;
reg [15:0] line2_data2;


reg data_out_en0;
reg data_out_en1;
reg data_out_en2;
reg hs_r0;
reg hs_r1;
reg hs_r2;


reg vs_r0;
reg vs_r1;
reg vs_r2;
wire[18:0] result_data;


line3x3 line3x3_inst(
.clken(data_in_en),
.clock(clk),
.shiftin(data_in),
.shiftout(),
.taps0x(line0),
.taps1x(line1),
.taps2x(line2)
);
//------------------------------------------------------------------------------
// Form an image matrix of three multiplied by three
//------------------------------------------------------------------------------
always @(posedge clk or negedge rst_n) begin
if(!rst_n) begin
line0_data0 <= 16'b0;
line0_data1 <= 16'b0;
line0_data2 <= 16'b0;

line1_data0 <= 16'b0;
line1_data1 <= 16'b0;
line1_data2 <= 16'b0;

line2_data0 <= 16'b0;
line2_data1 <= 16'b0;
line2_data2 <= 16'b0;

data_out_en0 <= 1'b0;
data_out_en1 <= 1'b0;
data_out_en2 <= 1'b0;

hs_r0 <= 1'b0;
hs_r1 <= 1'b0;
hs_r2 <= 1'b0;

vs_r0 <= 1'b0;
vs_r1 <= 1'b0;
vs_r2 <= 1'b0;
end
else if(data_in_en) begin
line0_data0 <= line0;
line0_data1 <= line0_data0;
line0_data2 <= line0_data1;

line1_data0 <= line1;
line1_data1 <= line1_data0;
line1_data2 <= line1_data1;

line2_data0 <= line2;
line2_data1 <= line2_data0;
line2_data2 <= line2_data1;


data_out_en0 <= data_in_en;
data_out_en1 <= data_out_en0;
data_out_en2 <= data_out_en1;

hs_r0 <= hs_in;
hs_r1 <= hs_r0;
hs_r2 <= hs_r1;

vs_r0 <= vs_in;
vs_r1 <= vs_r0;
vs_r2 <= vs_r1;
end
end




//-------------------------------------------------------------------
// line0_data0 line0_data1 line0_data2
// line1_data0 line1_data1 line1_data2
// line2_data0 line2_data1 line2_data2
//--------------------------------------------------------------------
always @(posedge clk or negedge rst_n) begin
if(!rst_n)
data_out <= 16'h0000;
else if(data_out_en1)
if((line0_data0 == 16'h0000) && (line0_data1 == 16'h0000) && (line0_data2 == 16'h0000) && (line1_data0 == 16'h0000) && (line1_data1 == 16'h0000) && (line1_data2 == 16'h0000) && (line2_data0 == 16'h0000) && (line2_data1 == 16'h0000) && (line2_data2 == 16'h0000))
data_out <= 16'hffff;
else if((line0_data0 == 16'hffff) && (line0_data1 == 16'hffff) && (line0_data2 == 16'hffff) && (line1_data0 == 16'hffff) && (line1_data1 == 16'hffff) && (line1_data2 == 16'hffff) && (line2_data0 == 16'hffff) && (line2_data1 == 16'hffff) && (line2_data2 == 16'hffff))
data_out <= 16'hffff;
else
data_out <= 16'h0000;
end

endmodule

4实验结果

图5 实验原图1

图6实验原图2

图7 实验结果图1

图8 实验结果图2

结果分析：图5和图7对比，比较粗的线都被查找出了边缘，只有最细的那条没有被提取出来，并且被加粗，原因是最细的线条只有三个像素当查找出边缘后显示为黑色，两边黑色连在一起所以线条就变粗了。图6和图8边缘查找没有问题。