图像翻转是常见的数字图像处理方式，分为水平翻转和垂直翻转。本文主要介绍 FPGA 实现图像翻转的基本思路，以及使用紫光同创 PGL22G 开发板实现数字图像水平翻转、垂直翻转的过程。
目录
1 水平翻转与垂直翻转
2 FPGA 布署与实现
2.1 功能与指标定义
2.2 逻辑设计
2.3 上板调试
1 水平翻转与垂直翻转
在数字图像处理中，图像翻转是指将图像进行水平或者垂直方向的翻转，使其呈现不同的效果，分为水平翻转和垂直翻转。
水平翻转是将图像沿着水平轴线进行翻转，将左半部分和右半部分进行交换。垂直翻转则是将图像沿着垂直轴线进行翻转，将上部分和下部分进行交换。
使用 FPGA 实现水平翻转时，由于每次向 DDR3 写入一行数据，因此可以借助写 DDR3 之前的 Dual-port RAM，将一行数据进行翻转，实现水平翻转的功能。FPGA 逻辑设计的大致思路是：写 Dual-port RAM 时，写地址从 0 增加；读 Dual-port RAM 写 DDR3 时，读地址从最大值逐步减小到 0 结束。
对于垂直翻转功能，则需要借助 DDR3 来实现。像素数据第 1 行写到第 N 行的位置，第 2 行写到第 N-1 行的位置，以此类推。FPGA 逻辑设计的大致思路是：每一行数据写入 DDR3 时，用图像高度减去原来的行地址，作为新的行地址。
2 FPGA 布署与实现
2.1 功能与指标定义
使用紫光同创 FPGA 平台实现图像翻转功能，FPGA 需要实现的功能与指标如下：
（1）与电脑的串口通信，用于接收上位机下发的图像数据，波特率为 256000 Bd/s；
（2）水平翻转与图像翻转：借助 Dual-port RAM 与 DDR3，分别实现水平翻转与垂直翻转功能；
（3）DDR3 读写控制，将处理前后的图像数据分别写入 DDR3 的不同区域，实现图像的拼接；
（4）HDMI 输出，输出一路 HDMI 信号源，用于将拼接后的图像显示在外接显示器上，分辨率为 1024×768。
2.2 逻辑设计
图像翻转工程主要的设计模块层次与功能说明如下：
| 模块名称 | 功能说明 | |
| top_uart | uart_rx_slice | 串口接收驱动模块 |
| uart_rx_parse | 串口数据解析模块，从上位机接收 8bit 原始图像 | |
| top_vidin | vidin_pipeline | pipeline 单元模块，缓存两行图像数据，并将数据提交到 ddr3 数据调度模块 |
| merge_out | dvi_timing_gen | HDMI 视频时序产生模块 |
| dvi_ddr_rd | 根据 HDMI 控制信号，提交读指令到 ddr3 数据调度模块 | |
| dvi_encoder | HDMI 输出编码（8b10b 编码）与输出驱动模块 | |
其中，vidin_pipeline 模块实现图像翻转功能，代码如下：
`timescale 1 ns/ 1 ps`include "../ddr_scheduler/ddr_parameter.vh"module vidin_pipeline (// System levelsys_rst,sys_clk,ddr_init_done,flip_lr,flip_ud,// pipeline input portspipeline_in_info,pipeline_in_data,pipeline_in_wren,pipeline_in_end,// pipeline output portspipeline_out_info,pipeline_out_data,pipeline_out_vld,pipeline_out_end,// User defined ports for ddr_schedulerddr_wr_baseaddr,ddr_wr_addr,ddr_wr_priority,ddr_wr_burstsize,ddr_wr_req,ddr_wr_ack,ddr_wr_end,ddr_wr_rden,ddr_wr_q,ddr_wr_mask
);// IO direction/register definitions
input sys_rst;
input sys_clk;
input ddr_init_done;
input flip_lr;
input flip_ud;input [31:0] pipeline_in_info;
input [31:0] pipeline_in_data;
input pipeline_in_wren;
input pipeline_in_end;output [31:0] pipeline_out_info;
output [31:0] pipeline_out_data;
output pipeline_out_vld;
output pipeline_out_end;input [`DDR_A_W-1:0] ddr_wr_baseaddr;
output [`DDR_A_W-1:0] ddr_wr_addr;
output ddr_wr_priority;
output [`DDR_BURST_W-1:0] ddr_wr_burstsize;
output ddr_wr_req;
input ddr_wr_ack;
input ddr_wr_end;
input ddr_wr_rden;
output [`DDR_D_W-1:0] ddr_wr_q;
output [`DDR_D_W/8-1:0] ddr_wr_mask;reg [31:0] pipeline_out_info;
reg [31:0] pipeline_out_data;
reg pipeline_out_vld;
reg pipeline_out_end;// internal signal declarations
reg [`DDR_CMD_W-1:0] ddr_cmd_data;
reg ddr_cmd_vld;reg [9:0] blk_mem_waddr;
reg [31:0] blk_mem_wdata;
reg blk_mem_wren;
reg [9:0] blk_mem_raddr;
wire [31:0] blk_mem_rdata;
reg blk_mem_rden;
reg blk_mem_rd_busy;
reg blk_mem_rd_end;
reg blk_mem_rd_vld;// line_buffer_inst: Dual-port ram for line pixel data buffer
blk_mem_1024x32b line_buffer_inst (.wr_data (blk_mem_wdata ), // input 32-bit.wr_addr (blk_mem_waddr ), // input 10-bit.wr_en (blk_mem_wren ), // input 1-bit.wr_clk (sys_clk ), // input 1-bit.wr_rst (sys_rst ), // input 1-bit.rd_addr (blk_mem_raddr ), // input 10-bit.rd_data (blk_mem_rdata ), // output 32-bit.rd_clk (sys_clk ), // input 1-bit.rd_rst (sys_rst ) // input 1-bit
);
// End of line_buffer_inst instantiationalways @(posedge sys_rst or posedge sys_clk) beginif (sys_rst) beginblk_mem_waddr <= {10{1'b0}};blk_mem_wdata <= {32{1'b0}};blk_mem_wren <= 1'b0;endelse beginblk_mem_wdata <= pipeline_in_data;blk_mem_wren <= pipeline_in_wren;// Use ping-pong storage hereif (pipeline_in_end) blk_mem_waddr <= {~blk_mem_waddr[9], {9{1'b0}}};else if (pipeline_in_wren) blk_mem_waddr <= {blk_mem_waddr[9], blk_mem_waddr[0+:9]+1'b1};end
endalways @(posedge sys_rst or posedge sys_clk) beginif (sys_rst) beginblk_mem_raddr <= {10{1'b0}};blk_mem_rden <= 1'b0;blk_mem_rd_busy <= 1'b0;blk_mem_rd_end <= 1'b0;blk_mem_rd_vld <= 1'b0;endelse beginif (~blk_mem_rd_busy && pipeline_in_end) beginblk_mem_rd_busy <= 1'b1;if (flip_lr == 1'b0) blk_mem_raddr <= {blk_mem_raddr[9], {9{1'b0}}};elseblk_mem_raddr <= {blk_mem_raddr[9], {9{1'b1}}};endelse if (blk_mem_rd_busy) begin// Use ping-pong storage hereif (flip_lr == 1'b0) beginif (& blk_mem_raddr[0+:9]) blk_mem_raddr <= {~blk_mem_raddr[9], {9{1'b0}}};else blk_mem_raddr <= {blk_mem_raddr[9], blk_mem_raddr[0+:9]+1'b1};endelse beginif (blk_mem_raddr[0+:9] == 0)blk_mem_raddr <= {~blk_mem_raddr[9], {9{1'b1}}};elseblk_mem_raddr <= {blk_mem_raddr[9], blk_mem_raddr[0+:9]-1'b1};end// Pull down read busy flagif (flip_lr == 1'b0) beginif (& blk_mem_raddr[0+:9]) blk_mem_rd_busy <= 1'b0;endelse beginif (blk_mem_raddr[0+:9] == 0)blk_mem_rd_busy <= 1'b0;endendblk_mem_rden <= blk_mem_rd_busy;blk_mem_rd_vld <= blk_mem_rden;if (blk_mem_rd_busy) beginif (flip_lr == 1'b0) beginif (& blk_mem_raddr[0+:9]) blk_mem_rd_end <= 1'b1;else blk_mem_rd_end <= 1'b0;endelse beginif (blk_mem_raddr[0+:9] == 0)blk_mem_rd_end <= 1'b1;else blk_mem_rd_end <= 1'b0;endendelseblk_mem_rd_end <= 1'b0;end
endalways @(posedge sys_rst or posedge sys_clk) beginif (sys_rst) beginpipeline_out_info <= {32{1'b0}};pipeline_out_data <= {32{1'b0}};pipeline_out_vld <= 1'b0;pipeline_out_end <= 1'b0;endelse beginif (pipeline_in_end) pipeline_out_info <= pipeline_in_info;pipeline_out_data <= blk_mem_rdata;pipeline_out_vld <= blk_mem_rd_vld;pipeline_out_end <= blk_mem_rd_end;end
end/
always @(posedge sys_rst or posedge sys_clk) beginif (sys_rst) beginddr_cmd_data <= {`DDR_CMD_W{1'b0}};ddr_cmd_vld <= 1'b0;endelse beginif (pipeline_in_end) beginddr_cmd_data[32+:`DDR_BURST_W] <= 8'h7F; // used fixed size here, 512 /4 -1 = 127if (flip_ud == 1'b0)ddr_cmd_data[0+:28] <= {pipeline_in_info[0+:16], 12'd0};elseddr_cmd_data[0+:28] <= {16'd383-pipeline_in_info[0+:16], 12'd0};endif (blk_mem_rd_end) ddr_cmd_vld <= 1'b1;else ddr_cmd_vld <= 1'b0;end
end// vid_ddr_wr_inst: ddr write control module
vid_ddr_wr vid_ddr_wr_inst (.sys_rst (sys_rst ), // input 1-bit.sys_clk (sys_clk ), // input 1-bit.ddr_init_done (ddr_init_done ), // input 1-bit.vid_cmd_data (ddr_cmd_data ), // input 40-bit.vid_cmd_vld (ddr_cmd_vld ), // input 1-bit.vid_img_data (blk_mem_rdata ), // input 32-bit.vid_img_data_vld (blk_mem_rd_vld ), // input 1-bit.ddr_wr_baseaddr (ddr_wr_baseaddr ), // input 27-bit.ddr_wr_addr (ddr_wr_addr ), // output 27-bit.ddr_wr_priority (ddr_wr_priority ), // output 1-bit.ddr_wr_burstsize (ddr_wr_burstsize ), // output 8-bit.ddr_wr_req (ddr_wr_req ), // output 1-bit.ddr_wr_ack (ddr_wr_ack ), // input 1-bit.ddr_wr_end (ddr_wr_end ), // input 1-bit.ddr_wr_rden (ddr_wr_rden ), // input 1-bit.ddr_wr_q (ddr_wr_q ), // output 128-bit.ddr_wr_mask (ddr_wr_mask ) // output 16-bit
);
// End of vid_ddr_wr_inst instantiationendmodule
2.3 上板调试
使用 PyQt5 和 OpenCV 库编写上位机程序，通过串口发送原始图像数据，以及水平翻转、垂直翻转参数。
# -*- Coding: UTF-8 -*-
import cv2
import sys
import struct
import numpy as np
from PyQt5 import Qt, QtGui, QtCore, QtWidgets, QtSerialPortclass mainWindow(Qt.QWidget):def __init__(self, com_port, parent=None):super(mainWindow, self).__init__(parent)self.setFixedSize(530, 384)self.setWindowTitle("PGL OpenCV Tool")self.flip_horizontal = Falseself.flip_vertical = False# 创建标签与按钮self.img_widget = QtWidgets.QLabel()self.btn1 = QtWidgets.QPushButton("打开")self.btn1.clicked.connect(self.getfile)self.btn2 = QtWidgets.QPushButton("关闭")self.btn2.clicked.connect(self.close)self.btn3 = QtWidgets.QPushButton("水平翻转")self.btn3.clicked.connect(self.flip_lr)self.btn4 = QtWidgets.QPushButton("垂直翻转")self.btn4.clicked.connect(self.flip_ud)# 创建布局centralLayout = QtWidgets.QVBoxLayout()centralLayout.addWidget(self.img_widget)bottomLayout = QtWidgets.QHBoxLayout()bottomLayout.addWidget(self.btn1)bottomLayout.addWidget(self.btn2)bottomLayout.addWidget(self.btn3)bottomLayout.addWidget(self.btn4)centralLayout.addLayout(bottomLayout)self.setLayout(centralLayout)# 串口对象self.COM = QtSerialPort.QSerialPort()self.COM.setPortName(com_port)self.COM.setBaudRate(256000)self.open_status = Falseself.row_cnt = 0self.img = Noneself.timer = QtCore.QTimer()self.timer.timeout.connect(self.sendImage)self.startup()def startup(self):"""Write code here to run once"""for com_port in QtSerialPort.QSerialPortInfo.availablePorts():print(com_port.portName())# Try open serial portif not self.COM.open(QtSerialPort.QSerialPort.ReadWrite):self.open_status = Falseprint("Open Serial Port failed.")else:self.open_status = Truedef flip_lr(self):"""水平翻转回调函数"""if self.flip_horizontal == False:self.flip_horizontal = Trueself.btn3.setStyleSheet("QPushButton{color:rgb(128,128,255)}")else:self.flip_horizontal = Falseself.btn3.setStyleSheet("QPushButton{color:rgb(0,0,0)}")def flip_ud(self):"""垂直翻转回调函数"""if self.flip_vertical == False:self.flip_vertical = Trueself.btn4.setStyleSheet("QPushButton{color:rgb(128,128,255)}")else:self.flip_vertical = Falseself.btn4.setStyleSheet("QPushButton{color:rgb(0,0,0)}")def getfile(self):"""获取图像路径"""fname = QtWidgets.QFileDialog.getOpenFileName(self, 'Open file','C:\\Users\\Administrator\\Pictures', "Image files(*.jpg *.png)")self.clipImage(fname[0])self.updateImage()self.sendImage()def clipImage(self, fname):"""读取并裁剪图片至512x384大小"""if fname:img = cv2.imread(fname, cv2.IMREAD_COLOR)img_roi = img[:384,:512,:]print(img_roi.shape)cv2.imwrite('./img_roi.png', img_roi)def updateImage(self):"""显示裁剪后的图像"""self.img_widget.setPixmap(QtGui.QPixmap('./img_roi.png'))self.img = cv2.imread('./img_roi.png')if self.open_status:self.timer.start(100)def sendImage(self):"""通过串口发送图片"""pattern = ">2BH{:d}B".format(512*3)# 获取图像翻转信息flip_flag = 0x00if self.flip_horizontal:flip_flag = flip_flag + 0x10if self.flip_vertical:flip_flag = flip_flag + 0x01# 发送图像数据if self.open_status:if self.row_cnt == 384+3:self.row_cnt = 0self.timer.stop()else:args1 = [0x55, flip_flag, self.row_cnt]args2 = [rgb for rgb in self.img[(self.row_cnt % 384),:].reshape(-1)]send_data = struct.pack(pattern, *(args1+args2))self.row_cnt += 1self.COM.write(send_data)def closeEvent(self, event):super().closeEvent(event)#self.slider_window.close()# 定时器停止self.timer.stop()if self.open_status:self.COM.close() # 关闭串口def main():app = QtWidgets.QApplication(sys.argv)window = mainWindow('COM21')window.show()#for win in (window, window.slider_window):# win.show()sys.exit(app.exec_())if __name__ == "__main__":main()
连接 HDMI 线和串口线，选择与发送图像，就可以看到 FPGA 的处理效果了。以下是水平翻转效果。
以下是垂直翻转效果。
