针对 基于海思开发板的屏幕截图程序(一)作了改进，上篇文章的截图结果不正确的原因是：我公司的开发板上fb0中设置的图片格式为ARGB1555，但是我将它作为RGB565来使用，导致转换出来的图片数据不正确，所以压缩后的图片自然会失真。

关键函数是：ARGB1555_to_RGB24() // 将ARGB1555格式的图像数据转换成RGB24的格式。完整代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include <fcntl.h>
#include <malloc.h>
#include <linux/fb.h>
#include <jpeglib.h>
#include <jerror.h>
#include <errno.h>extern int errno;/*功能：		获取当前系统时间返回值：	指向时间字符串的开始位置
*/
static const char* getCurTime()					// 获取当前系统时间
{static char ret[30] = {0};time_t t;struct tm *tp;t = time(NULL);tp = localtime(&t);memset(ret, 0, sizeof(ret));sprintf(ret, "%02d%02d%02d_%02d%02d%02d", tp->tm_year+1900, tp->tm_mon+1, tp->tm_mday, tp->tm_hour, tp->tm_min, tp->tm_sec);return ret;
}/*功能:		RGB565转RGB24函数rgb565:		指向存放rgb565数据的起始地址rgb24:		指向存放rgb24数据的起始地址width:		屏幕(分辨率)的宽度height:		屏幕(分辨率)的高度
*/ 
int RGB565_to_RGB24(unsigned char *rgb565, unsigned char *rgb24, int width, int height)
{int i;int whole = width * height;				// 屏幕像素点个数unsigned char r, g, b;					// 目标缓冲区是RGB格式, 每个分量占1字节, 所以用ucharunsigned short int *pix565;				// 每像素信息占2字节, 所以用short类型pix565 = (unsigned short int *)rgb565;for(i = 0; i < whole; i++){r = ((*pix565) >> 11) & 0x1f;*rgb24 = (r << 3) | (r >> 2);rgb24++;							// 目标像素点后移g = ((*pix565) >> 5) & 0x3f;*rgb24 = (g << 2) | (g >> 4);rgb24++;b = (*pix565) & 0x1f;*rgb24 = (b << 3) | (b >> 2);rgb24++;pix565++;							// 源像素点后移}return 0;
}/*功能:			将ARGB1555格式的图片数据转换成RGB24的图片数据返回值:			0argb1555:[in]	源缓冲区地址, 指向存放argb1555数据的起始地址rgb24:	[out]	目标缓冲区地址, 指向存放rgb24数据的起始地址xres:			屏幕分辨率的宽度yres:			屏幕分辨率的高度
*/
int ARGB1555_to_RGB24(unsigned char *argb1555, unsigned char *rgb24, int xres, int yres)
{int i;int whole = xres * yres;unsigned char r, g, b;unsigned short int *pix1555;pix1555 = (unsigned short int *)argb1555;for(i = 0; i < whole; i++){//	*pix1555 &= 0x7FFFFF;				// 透明分量置为0r = ((*pix1555) >> 10) & 0x1f;		// 取颜色分量: R*rgb24++ = (r << 3) | (r >> 2);g = ((*pix1555) >> 5) & 0x1f;		// 取分量: G*rgb24++ = (g << 3) | (g >> 2);b = (*pix1555) & 0x1f;				// 取分量: B*rgb24++ = (b << 3) | (b >> 2);pix1555++;if(rgb24[-3] == 0xFF && rgb24[-2] == 0 && rgb24[-1] == 0xFF)	// RGB = 0xFF00FFrgb24[-3] = 0;												// 修改RGB = 0x0000FF(将粉红色替换成蓝色)}return 0;
}/*功能:	jpeg压缩函数返回值:	0: 成功, -1: 失败rgb：	指向存放rgb24数据的起始地址width：	屏幕(分辨率)的宽度height:	屏幕(分辨率)的高度
*/
int jpeg_compress(unsigned char *rgb, int width, int height)
{char outfile[100] = {0};struct jpeg_compress_struct cinfo;struct jpeg_error_mgr jerr;FILE * pf = NULL;JSAMPROW row_pointer[1];int row_stride;sprintf(outfile, "snap_%s.jpg", getCurTime());if ((pf = fopen(outfile, "wb")) == NULL){printf("Can not create output file, please check!\n");return -1;}cinfo.err = jpeg_std_error(&jerr);jpeg_create_compress(&cinfo);jpeg_stdio_dest(&cinfo, pf);cinfo.image_width = width;cinfo.image_height = height;cinfo.input_components = 3;				// 1-灰度图，3-彩色图// 输入数据格式为RGBcinfo.in_color_space = JCS_RGB;			// JCS_GRAYSCALE-灰度图，JCS_RGB-彩色图jpeg_set_defaults(&cinfo);jpeg_set_quality(&cinfo, 80, TRUE);		// 设置压缩质量：80jpeg_start_compress(&cinfo, TRUE);		// 开始压缩过程row_stride = width * 3;					// row_stride: 每一行的字节数while (cinfo.next_scanline < cinfo.image_height){row_pointer[0] = &rgb[cinfo.next_scanline * row_stride];(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);}jpeg_finish_compress(&cinfo);			// 完成压缩过程fclose(pf);jpeg_destroy_compress(&cinfo);			// 释放资源return 0;
}int main()
{int fd;struct fb_var_screeninfo fb_var_info;struct fb_fix_screeninfo fb_fix_info;unsigned char *trgb;unsigned char *rgb;int buffer_size;const char *dev = "/dev/fb0";// 打开framebuffer设备fd = open(dev, O_RDONLY);if(fd < 0){printf("fd=%d, error=[%d: %s]\n", fd, errno, strerror(errno));return -1;}// 获取LCD的可变参数ioctl(fd, FBIOGET_VSCREENINFO, &fb_var_info);// 一个像素多少位printf("bits_per_pixel: %d\n", fb_var_info.bits_per_pixel);printf("分辨率: %d x %d\n", fb_var_info.xres, fb_var_info.yres);printf("颜色分量值: (A, R, G, B) = (%d, %d, %d, %d)bits\n", fb_var_info.transp.length, fb_var_info.red.length, fb_var_info.green.length, fb_var_info.blue.length);printf("颜色分量偏移: (A, R, G, B) = (%d, %d, %d, %d)\n", fb_var_info.transp.offset, fb_var_info.red.offset, fb_var_info.green.offset, fb_var_info.blue.offset);// 获取LCD的固定参数ioctl(fd, FBIOGET_FSCREENINFO, &fb_fix_info);// 一帧大小printf("smem_len: %#X\n", fb_fix_info.smem_len);// 一行大小printf("line_length: %#X\n", fb_fix_info.line_length);// 一帧大小buffer_size = (fb_var_info.xres * fb_var_info.yres * fb_var_info.bits_per_pixel / 8);trgb = (unsigned char *)malloc(buffer_size);if(trgb == NULL)exit(0);rgb = (unsigned char *)malloc(fb_var_info.xres * fb_var_info.yres * 3);if(rgb == NULL)goto here;if(read(fd, trgb, buffer_size) < 0)		// 获取一帧数据{printf("read failed!\n");goto read_fail;}//	RGB565_to_RGB24(trgb, rgb, fb_var_info.xres, fb_var_info.yres);			// 将RGB565转换成RGB24格式ARGB1555_to_RGB24(trgb, rgb, fb_var_info.xres, fb_var_info.yres);		// 将ARGB1555转换成RGB24格式if(jpeg_compress(rgb, fb_var_info.xres, fb_var_info.yres) < 0)			// jpeg压缩失败printf("Jpeg compress failed!\n");read_fail:free(rgb);
here:free(trgb);close(fd);return 0;
}

至此，程序运行后得到的图片效果与开发板上所看到的效果完全一样，至少肉眼是分不出差异！

makefile文件如下：

CC=arm-hismall-linux-gcca: a.c$(CC) -o $@ $^ -I/opt/jpeg/include /opt/jpeg/lib/libjpeg.aclean:rm -f *.o a