Y通道： 表示图像的强度，亮度 Cb通道： 表示图像蓝色 色度 Cr通道： 表示图像红色 色度

然后减少颜色信息减少存储空间 参考资料

用RGB表示图片，其中GRB三个通道分别如下： 用YCbCr图像如下：

1. 计算公式
2. 流水线
3. 行信号打拍

`timescale 1ns / 1ps // // Company:  // Engineer:  //  // Create Date: 2022/04/19 10:02:26 // Design Name:  // Module Name: RGB888_YCbCr444 // Project Name:  // Target Devices:  // Tool Versions:  // Description:  //  // Dependencies:  //  // Revision: // Revision 0.01 - File Created // Additional Comments: //  // module RGB888_YCbCr444 (  //global clock  input     clk,      //cmos video pixel clock  input     rst_n,    //global reset   //Image data prepred to be processd  input     per_frame_vsync, //Prepared Image data vsync valid signal  input     per_frame_href,  //Prepared Image data href vaild signal  input     per_frame_clken, //Prepared Image data output/capture enable clock   input  [7:0]  per_img_red,  //Prepared Image red data to be processed  input  [7:0]  per_img_green,  //Prepared Image green data to be processed  input  [7:0]  per_img_blue,  //Prepared Image blue data to be processed    //Image data has been processd  output    post_frame_vsync, //Processed Image data vsync valid signal  output    post_frame_href, //Processed Image data href vaild signal  output    post_frame_clken, //Processed Image data output/capture enable clock   output  [7:0] post_img_Y,   //Processed Image brightness output  output  [7:0]	post_img_Cb,		//Processed Image blue shading output
	output		[7:0]	post_img_Cr			//Processed Image red shading output
);

	//--------------------------------------------
	/********************************************* //Refer to <OV7725 Camera Module Software Applicaton Note> page 5 Y = (77 *R + 150*G + 29 *B)>>8 Cb = (-43*R - 85 *G + 128*B)>>8 + 128 Cr = (128*R - 107*G - 21 *B)>>8 + 128 Y = (77 *R + 150*G + 29 *B)>>8 Cb = (-43*R - 85 *G + 128*B + 32768)>>8 Cr = (128*R - 107*G - 21 *B + 32768)>>8 **********************************************/
	//Step 1
	reg	[15:0]	img_red_r0,		img_red_r1,		img_red_r2;	
	reg	[15:0]	img_green_r0,	img_green_r1,	img_green_r2; 
	reg	[15:0]	img_blue_r0,	img_blue_r1,	img_blue_r2;

	// 第一级流水线：执行乘法
	always@(posedge clk or negedge rst_n)begin
		if(!rst_n)
			begin
			img_red_r0		<=	0; 	
			img_red_r1		<=	0; 	
			img_red_r2		<=	0; 	
			img_green_r0	<=	0; 	
			img_green_r1	<=	0; 	
			img_green_r2	<=	0; 	
			img_blue_r0		<=	0; 	
			img_blue_r1		<=	0; 	
			img_blue_r2		<=	0; 	
			end
		else
			begin
			img_red_r0		<=	per_img_red 	* 	8'd77; 
			img_red_r1		<=	per_img_red 	* 	8'd43; 
			img_red_r2		<=	per_img_red 	* 	8'd128;
			img_green_r0	<=	per_img_green 	* 	8'd150;
			img_green_r1	<=	per_img_green 	* 	8'd85; 
			img_green_r2	<=	per_img_green 	* 	8'd107;
			img_blue_r0		<=	per_img_blue 	* 	8'd29; 
			img_blue_r1		<=	per_img_blue 	* 	8'd128;
			img_blue_r2		<=	per_img_blue 	* 	8'd21; 
			end
	end

	//--------------------------------------------------
	//Step 2
	reg	[15:0]	img_Y_r0;
	reg	[15:0]	img_Cb_r0; 
	reg	[15:0]	img_Cr_r0; 

	// 第二级流水线：执行加法
	always@(posedge clk or negedge rst_n)begin
		if(!rst_n)
			begin
			img_Y_r0	<=	0; 	
			img_Cb_r0	<=	0; 	
			img_Cr_r0	<=	0; 	
			end
		else
			begin
			img_Y_r0	<=	img_red_r0 	+ 	img_green_r0 	+ 	img_blue_r0; 
			img_Cb_r0	<=	img_blue_r1 - 	img_red_r1 		- 	img_green_r1	+	16'd32768; 
			img_Cr_r0	<=	img_red_r2 	+ 	img_green_r2 	+ 	img_blue_r2		+	16'd32768; 
			end
	end

	//--------------------------------------------------
	//Step 3
	reg	[7:0]	img_Y_r1;
	reg	[7:0]	img_Cb_r1; 
	reg	[7:0]	img_Cr_r1; 

	// 第三级流水线：右移8位=除以256 ？？？？？？
	always@(posedge clk or negedge rst_n)begin
		if(!rst_n)
			begin
			img_Y_r1	<=	0; 	
			img_Cb_r1	<=	0; 	
			img_Cr_r1	<=	0; 	
			end
		else
			begin
			img_Y_r1	<=	img_Y_r0[15:8];
			img_Cb_r1	<=	img_Cb_r0[15:8];
			img_Cr_r1	<=	img_Cr_r0[15:8]; 
			end
	end

	//------------------------------------------
	//lag 3 clocks signal sync 
	// 上面有3级流水线，因此经历了3个时钟，于是需要把输入的行、使能信号等进行3次打拍操作
	// 这里的打拍操作比较厉害，值得学习！！
	//---------------------------------------------
	reg	[2:0]	per_frame_vsync_r;
	reg	[2:0]	per_frame_href_r;	
	reg	[2:0]	per_frame_clken_r;
	
	always@(posedge clk or negedge rst_n)begin
		if(!rst_n)
			begin
			per_frame_vsync_r <= 0;
			per_frame_href_r  <= 0;
			per_frame_clken_r <= 0;
			end
		else
			begin
			per_frame_vsync_r 	<= 	{ 
        per_frame_vsync_r[1:0], 	per_frame_vsync};
			per_frame_href_r	<= 	{ 
        per_frame_href_r [1:0], 	per_frame_href};
			per_frame_clken_r 	<= 	{ 
        per_frame_clken_r[1:0], 	per_frame_clken};
			end
	end
	
	assign	post_frame_vsync 	= 	per_frame_vsync_r[2];
	assign	post_frame_href 	= 	per_frame_href_r [2];
	assign	post_frame_clken 	= 	per_frame_clken_r[2];
	
	// 当有行信号时，就输出
	assign	post_img_Y 	= 	post_frame_href ? img_Y_r1 : 8'd0;
	assign	post_img_Cb =	post_frame_href ? img_Cb_r1: 8'd0;
	assign	post_img_Cr = 	post_frame_href ? img_Cr_r1: 8'd0;
	
endmodule