From: http://blog.chinaunix.net/uid-24789420-id-3191806.html

一、概述

        最近看到网上有人问怎么用C语言实现屏幕截图，刚好自己也在研究Linux驱动，于是花了半天时间把Linux的FrameBuffer驱动看懂了个七八，接着就动手写了个LCD屏幕截图的应用程序。

     一些说明：

     1. 板子LCD的分辨率为480x272，像素格式为RGB565。

     2. 程序首先获取LCD的一些参数 ，然后将获取到的一帧数据转换为RGB24格式，最后用jpeglib库压缩为jpg格式的图片。

　  3. 在嵌入式Linux的板子上测试通过。

 

二、实现

       程序中有注释，不多说，直接上程序：

#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <malloc.h>
#include <linux/fb.h>
#include <jpeglib.h>
#include <jerror.h>/*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;unsigned char r, g, b;unsigned short int *pix565;pix565 = (unsigned short int *)rgb565;for(i = 0;i < whole;i++){    r = ((*pix565)>>11)&0x1f;*rgb24 = (r<<3) | (r>>2);rgb24++;g = ((*pix565)>>5)&0x3f;*rgb24 = (g<<2) | (g>>4);rgb24++;b = (*pix565)&0x1f;*rgb24 = (b<<3) | (b>>2);rgb24++;pix565++;    }return 1;
}/*jpeg压缩函数*@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)
{struct jpeg_compress_struct cinfo;struct jpeg_error_mgr jerr;FILE * outfile;JSAMPROW row_pointer[1];int row_stride;cinfo.err = jpeg_std_error(&jerr);jpeg_create_compress(&cinfo);// 输出文件名为：out.jpgif ((outfile = fopen("out.jpg", "wb")) == NULL){printf("can not open out.jpg\n");return -1;}jpeg_stdio_dest(&cinfo, outfile);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(outfile);jpeg_destroy_compress(&cinfo);			// 释放资源return 1;
}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;// 打开framebuffer设备fd = open("/dev/fb0", O_RDONLY);if(fd < 0){printf("can not open dev\n");exit(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);// x分辨率printf("xres: %d\n", fb_var_info.xres);// y分辨率printf("yres: %d\n", fb_var_info.yres);// r分量长度(bit)printf("red_length: %d\n", fb_var_info.red.length);// g分量长度(bit)printf("green_length: %d\n", fb_var_info.green.length);// b分量长度(bit)printf("blue_length: %d\n", fb_var_info.blue.length);// t(透明度)分量长度(bit)printf("transp_length: %d\n", fb_var_info.transp.length);// r分量偏移printf("red_offset: %d\n", fb_var_info.red.offset);// g分量偏移printf("green_offset: %d\n", fb_var_info.green.offset);// b分量偏移printf("blue_offset: %d\n", fb_var_info.blue.offset);// t分量偏移printf("transp_offset: %d\n", fb_var_info.transp.offset);// 获取LCD的固定参数ioctl(fd, FBIOGET_FSCREENINFO, &fb_fix_info);// 一帧大小printf("smem_len: %d\n", fb_fix_info.smem_len);// 一行大小printf("line_length: %d\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;}// 格式转换RGB565_to_RGB24(trgb, rgb, fb_var_info.xres, fb_var_info.yres);// jpeg压缩if(jpeg_compress(rgb, fb_var_info.xres, fb_var_info.yres) < 0)printf("compress failed!\n");        read_fail:free(rgb);
here:free(trgb);close(fd);return 0;
}

注意：编译时加上" -ljpeg"