一、前言
在4M内存的开发板上实现图片文件文字叠加面临严峻挑战，实际可用内存不足1M。常规方案依赖第三方库，但内存无法承受。为此，采用将图片还原为YUV文件，通过计算分量坐标完成文字叠加，并将文字以十六进制数组形式定义在头文件中编译进程序，从而解决内存不足问题。参考了CSDN博客中关于YUV图像叠加文字的实现算法，但该方案仅支持数字及两个符号，扩展性有限。针对生成点阵软件缺失的问题，现有工具仅支持LED屏点阵数组（十六进制或二进制）。为实现扩展，提出两种方案：一是自行编写程序扩展图案数组；二是修改算法以支持二进制点阵。最终选择第二种方式，因其实现更简单且内存占用更小。
二、YUV分量计算头文件
根据个人需求修改后的头文件，digital_led.h
#ifndef _DIGITAL_LED_H__
#define _DIGITAL_LED_H__
#define BACKGROUND_BLACK 0 //白字，黑色背景
#define BACKGROUND_TRANSPARENT 1 //白字，透明背景
#define BACKGROUND_NULL 2 //半透明，无背景
#define COLOR_YUV420p 0
#define COLOR_NV12 1 //420SP,Y平面,UV非平面:YYYYYYYYUVUV --- 没有经过测试，不知道是否存在问题
#define COLOR_YUV422p 2
#define COLOR_YUV444p 3
#define COLOR_Yp 9 //Y平面模型都小于这个值
#define TAB_START_CHAR ' ' //字库起始字符
#define TAB_END_CHAR '~' //字库结束字符
static int digital_width = 16;
static int digital_height = 16;
static int gap_width = 0;
//这里直接设置为黑背景
int overOSD(int colorformat, unsigned char *yuvOut, const unsigned char *osd, int osdW, int osdH, int yuvW, int yuvH , int x, int y);
//白字，透明背景
int overOSD1(int colorformat, unsigned char *yuvOut, const unsigned char *osd, int osdW, int osdH, int yuvW, int yuvH , int x, int y);
//直接将Y分量取反，不改变UV分量，达到字体半透明的效果
int overOSD2(int colorformat, unsigned char *yuvOut, const unsigned char *osd, int osdW, int osdH, int yuvW, int yuvH , int x, int y);
//多字符写入
void overinfo(char*info, int colorformat, int overtype, unsigned char *yuvOut ,int yuvW, int yuvH , int x, int y);
static const unsigned char tilde_sign[32] = {//~
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00111110, 0b00110000,
0b01110111, 0b01110000,
0b01110011, 0b11110000,
0b01110001, 0b11100000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000,
0b00000000, 0b00000000
};
static const unsigned char* DigitalArray[] = {
&space_sign[0], &exclamation_sign[0], &double_quotation[0], £_sign[0], &dollar_sign[0], &percent_sign[0], &ersand_sign[0], &single_quotation[0], &left_bracket[0], &right_bracket[0],
&asterisk_sign[0], &plus_sign[0], &omma_sign[0], &mimus_sign[0], &point_sign[0], &diagnal_bar[0], &digital_0[0], &digital_1[0], &digital_2[0], &digital_3[0],
&digital_4[0], &digital_5[0], &digital_6[0], &digital_7[0], &digital_8[0], &digital_9[0], &colon_sign[0], &semico_sign[0], &less_than[0], &equal_than[0],
&greater_than[0], &question_mark[0], &aite_symbol[0], &caplital_letter_A[0], &caplital_letter_B[0], &caplital_letter_C[0], &caplital_letter_D[0], &caplital_letter_E[0], &caplital_letter_F[0], &caplital_letter_G[0],
&caplital_letter_H[0], &caplital_letter_I[0], &caplital_letter_J[0], &caplital_letter_K[0], &caplital_letter_L[0], &caplital_letter_M[0], &caplital_letter_N[0], &caplital_letter_O[0], &caplital_letter_P[0], &caplital_letter_Q[0],
&caplital_letter_R[0], &caplital_letter_S[0], &caplital_letter_T[0], &caplital_letter_U[0], &caplital_letter_V[0], &caplital_letter_W[0], &caplital_letter_X[0], &caplital_letter_Y[0], &caplital_letter_Z[0], &square_brackets_l[0],
&backslash_sign[0], &square_brackets_r[0], &power_sign[0], &bash_sign[0], &inverted_quotation[0], &small_letter_a[0], &small_letter_b[0], &small_letter_c[0], &small_letter_d[0], &small_letter_e[0],
&small_letter_f[0], &small_letter_g[0], &small_letter_h[0], &small_letter_i[0], &small_letter_j[0], &small_letter_k[0], &small_letter_l[0], &small_letter_m[0], &small_letter_n[0], &small_letter_o[0],
&small_letter_p[0], &small_letter_q[0], &small_letter_r[0], &small_letter_s[0], &small_letter_t[0], &small_letter_u[0], &small_letter_v[0], &small_letter_w[0], &small_letter_x[0], &small_letter_y[0],
&small_letter_z[0], &left_brace[0], &or_sign[0], &right_brace[0], &tilde_sign[0]
};
#endif
三、YUV分量计算的源文件
根据个人需求修改后的源文件，digital_led.c
#include2;i++){
for(j=0;j2) + j+x] = 0x80;
}
}
}else if(colorformat == COLOR_YUV420p){//yuv420p
//y: 这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
int i = 0, j = 0;
for (i = 0; i < osdH * osdW / 8; i++)
{
unsigned char osddata = osd[i];
for (j = 0; j < 8; j++)
{
if(((osddata << j) & 0x80) == 0x80){
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = 0xff;
}else{
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = 0x00;
}
}
}
//u
//这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
//需要保证w和h是偶数
yuvOut+=yuvW*yuvH;
for(i=0;i2;i++){
for(j=0;j2;j++){
yuvOut[yuvW/2 *(i+y/2) + j+x/2] = 0x80;
}
}
//v 这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
yuvOut+=yuvW*yuvH/4;
for(i=0;i2;i++){
for(j=0;j2;j++){
yuvOut[yuvW/2 *(i+y/2) + j+x/2] = 0x80;
}
}
}
return 1;
}
//白字，透明背景
int overOSD1(int colorformat,unsigned char *yuvOut , const unsigned char *osd, int osdW, int osdH, int yuvW, int yuvH , int x, int y)
{
if((x + osdW) > yuvW || (y + osdH) > yuvH){
printf("pram errn");
return 0;
}
if(colorformat == COLOR_NV12){//NV12
//y:
int i=0,j=0;
for (i = 0; i < osdH * osdW / 8; i++)
{
unsigned char osddata = osd[i];
for (j = 0; j < 8; j++)
{
if(((osddata << j) & 0x80) == 0x80){
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = 0xff;
}else{
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = 0x00;
}
}
}
//uv 这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
yuvOut += yuvW * yuvH;
for (i = 0; i < osdH * osdW / 8; i++)//
{
unsigned char osddata = osd[i];
for (j = 0; j < 8; j++)
{
if(((osddata << j) & 0x80) == 0x80){
int index_y = yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x);
yuvOut[(index_y / yuvW) / 2 * (yuvW / 2) * 2 + (index_y % yuvW)] = 0x80;//u
yuvOut[(index_y / yuvW) / 2 * (yuvW / 2) * 2 + (index_y % yuvW) + 1] = 0x80;//v
}
}
}
}else if(colorformat == COLOR_YUV420p){//YUV420p
//y:
int i=0,j=0;
for (i = 0; i < osdH * osdW / 8; i++)
{
unsigned char osddata = osd[i];
for (j = 0; j < 8; j++)
{
if(((osddata << j) & 0x80) == 0x80){
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = 0xff;
}
}
}
//u 这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
yuvOut += yuvW * yuvH;
for (i = 0; i < osdH * osdW / 8; i ++)
{
unsigned char osddata = osd[i];
for (j = 1; j < 8; j ++)
{
if(((osddata << j) & 0x80) == 0x80){
int index_y = yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x);
if((index_y / yuvW) % 2 == 0)
yuvOut[(index_y / yuvW) / 2 * (yuvW / 2) + (index_y % yuvW) / 2] = 0x80;
}
}
}
//v 这里的坐标计算尽量保持原本的意思，看起来比较冗余，可以简化提供效率
yuvOut += yuvW * yuvH / 4;
for (i = 0; i < osdH * osdW / 8; i ++)
{
unsigned char osddata = osd[i];
for (j = 1; j < 8; j ++)
{
if(((osddata << j) & 0x80) == 0x80){
int index_y = yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x);
if((index_y / yuvW) % 2 == 0)
yuvOut[(index_y / yuvW) / 2 * (yuvW / 2) + (index_y % yuvW) / 2] = 0x80;
}
}
}
}
return 1;
}
//直接将Y分量取反，不改变UV分量
int overOSD2(int colorformat, unsigned char *yuvOut, const unsigned char *osd, int osdW, int osdH, int yuvW, int yuvH , int x, int y)
{
if((x + osdW) > yuvW || (y + osdH) > yuvH){
printf("pram errn");
return 0;
}
if(colorformat <= COLOR_Yp){
//y
int i = 0, j = 0;
for (i = 0; i < osdH * osdW / 8; i++)
{
unsigned char osddata = osd[i];
for (j = 0; j < 8; j++)
{
if(((osddata << j) & 0x80) == 0x80){
yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)] = ~yuvOut[yuvW * (i / (osdW / 8) + y) + (j + (i%(osdW/8)) * 8 + x)];
}
}
}
}
return 1;
}
//多字符写入
void overinfo(char*info,int colorformat,int overtype,unsigned char *yuvOut ,int yuvW, int yuvH , int x, int y)
{
int infolen = strlen(info);
printf("infolen = %dn", infolen);
int i = 0;
int postionX = x;
int postionY = y;
for(i = 0; i < infolen; i++){
if(info[i] == 'n'){
postionX = x;
postionY += digital_height;
}else if(TAB_START_CHAR <= info[i] && info[i] <= TAB_END_CHAR){
int ret = 1;
if(overtype == BACKGROUND_BLACK){
ret = overOSD(colorformat, yuvOut, DigitalArray[info[i] - TAB_START_CHAR], digital_width, digital_height, yuvW, yuvH, postionX, postionY);
}else if(overtype == BACKGROUND_TRANSPARENT){
ret = overOSD1(colorformat, yuvOut, DigitalArray[info[i] - TAB_START_CHAR], digital_width, digital_height, yuvW, yuvH, postionX, postionY);
}else if(overtype == BACKGROUND_NULL){
ret = overOSD2(colorformat, yuvOut, DigitalArray[info[i] - TAB_START_CHAR], digital_width, digital_height, yuvW, yuvH, postionX, postionY);
}else{
printf("error: overtype unknown definition %dn", overtype);
return;
}
if(ret == 0){//坐标超过，换行写入
postionX = x;
postionY += digital_height;
i --;
}else if(ret == 1){
postionX += digital_width;
}else{//未知返回
printf("error: unknown return %dn", ret);
}
if((postionY + digital_height) > yuvH){
printf("stop drawing at '%c'! postionY is greter than yuvH!n", info[i]);
return;
}
}else{
printf("an unknown symbol has been skipped: %cn", info[i]);
}
}
}
四、测试说明
代码中多字符写入函数包含判断换行符和溢出逻辑，调用测试如下：
overinfo("1n234567890nabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!@#$^*(){}[] :;%|/><.,`qweroiugsdmnxcvzvjsqodasjdfaoiugfkajhOWEYRAHDFAYEWFAJDSLAKWEORYFASDFJALKSDFWQOURTYASGDF", COLOR_YUV420p, BACKGROUND_NULL, buf, w, h, x + 10, y + (digital_height * 2));
原图片和处理后的图片对比展示如下：
五、字符图案扩展
使用在线软件进行字符图案扩展，地址如下：点阵生成软件|字模提取（支持中文） - LED、OLED、LCD、单片机在线取模、中文点阵取模软件、在线显示屏取模 - Arduino|STM32|STM8 - 文字或图片点阵生成软件 (zhetao.com)
