jpeg库下载地址：http://www.ijg.org/交叉编译三部曲：A ./configure --host=arm-linux-gcc --prefix=/home/flying/jpeg-installB  makeC  make install

jpeg库是解压jpeg/jpg图片或将图片压缩为jpeg/jpg格式所用到的库，使用起来比较简单！jpeg/jpg解码过程：1. 创建jpeg对象和错误处理对象struct jpeg_decompress_struct cinfo;struct jpeg_error_mgr         jerr; 2. 将错误处理对象绑定到jpeg对象上EXTERN(struct jpeg_error_mgr *) jpeg_std_errorJPP((struct jpeg_error_mgr * err));3. 初始化jpeg对象#define jpeg_create_compress(cinfo) \jpeg_CreateCompress((cinfo), JPEG_LIB_VERSION, \(size_t) sizeof(struct jpeg_compress_struct))4. 指定解压数据源（有两种方式）a. EXTERN(void) jpeg_mem_src JPP((j_decompress_ptr cinfo, const unsigned char * inbuffer, unsigned long insize));参数一： jpeg对象地址参数二： 储存jpeg数据源缓冲区参数三： 缓冲区数据源大小b. EXTERN(void) jpeg_stdio_src JPP((j_decompress_ptr cinfo, FILE * infile));参数一： jpeg对象地址参数二： 要解压的jpeg图片的文件指针5. 填充cinfo对象的缺省信息，常见的可用信息包括图像的宽：       cinfo.image_width，高：       cinfo.image_height，色彩空间：  cinfo.jpeg_color_space，颜色通道数： cinfo.num_components等。EXTERN(int) jpeg_read_header JPP((j_decompress_ptr cinfo,boolean require_image));6. 为解压设定参数**(依情况而定）**比如解压的图片与原图的缩放比例为1/2，这可以设置参数cinfo.scale_num   = 1cinfo.scale_denom = 27. 开始解压EXTERN(boolean) jpeg_start_decompress JPP((j_decompress_ptr cinfo));在完成解压缩操作后，会将解压后的图像信息填充至cinfo结构中。比如，输出图像宽度cinfo.output_width，输出图像高度cinfo.output_height，每个像素中的颜色通道数cinfo.output_components（比如灰度为1，全彩色为3）等。一般情况下，这些参数是在jpeg_start_decompress后才被填充到cinfo中的，如果希望在调用jpeg_start_decompress之前就获得这些参数，可以通过调用jpeg_calc_output_dimensions()的方法来实现。8. 取数据解压出来的数据是按照行取出的，从左到右，从上到下的顺序，每个像素对应的各颜色或灰度通道数据是依次存储，24位RGB图解压后的颜色通道排序是R，G，B，R，G，B......我们可以使用此函数取出循环取出数据：extern JDIMENSION jpeg_read_scanlines(j_decompress_ptr, JSAMPARRAY,JDIMENSION);参数二： 一般来说就是unsigned char *，表示保存数据的缓冲区参数三： 表示要读取的行数9. 解压完毕释放资源boolean jpeg_finish_decompress(j_decompress_ptr cinfo);后续不需要使用jpeg对象：void jpeg_destroy_decompress(j_decompress_ptr cinfo);如果在后续还需使用jpeg对象，则使用：void jpeg_abort_decompress(j_decompress_ptr cinfo);

实例：
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <linux/fb.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdbool.h>#include "jpeglib.h"
#include "my_err.h"struct image_info
{int width;int height;int pixel_size;
};//将图片显示到LCD屏幕上，最后两个参数指定显示的原点坐标
void write_jpeg_to_lcd(unsigned char *lcdmem, unsigned char *rgb_buffer, struct fb_var_screeninfo *vinfo, struct image_info *image_info, size_t xoffset, size_t yoffset)
{assert(lcdmem);assert(rgb_buffer);assert(vinfo);assert(image_info); int x, y;size_t r_offset = vinfo->red.offset / 8;size_t g_offset = vinfo->green.offset / 8;size_t b_offset = vinfo->blue.offset / 8;for (y = 0; (y < vinfo->yres - yoffset) && (y < image_info->height); ++y) {for (x = 0; (x < vinfo->xres - xoffset) && (x < image_info->width); ++x) {size_t image_offset     =   (x * image_info->pixel_size) + (image_info->width * image_info->pixel_size * y);size_t lcd_offset       =   ((x + xoffset) * vinfo->bits_per_pixel / 8) + ((y + yoffset) * vinfo->xres * vinfo->bits_per_pixel /8);memcpy(lcdmem + lcd_offset + r_offset, rgb_buffer + image_offset, 1);memcpy(lcdmem + lcd_offset + g_offset, rgb_buffer + image_offset + 1, 1);memcpy(lcdmem + lcd_offset + b_offset, rgb_buffer + image_offset + 2, 1);}}
}void read_image_from_file(int fd, unsigned char *jpeg_buffer, size_t image_size)
{assert(jpeg_buffer);int nread = 0;while (image_size > 0) {nread = read(fd, jpeg_buffer, image_size);if (nread < 0) {if (EINTR == errno) {continue;} else {err_sys("read error");}}image_size -= nread;jpeg_buffer += nread;}
}int main(int argc, char **argv)
{if (2 != argc) {err_quit("Usage: %s <*.jpeg/jpg>\n", argv[1]);}int image_fd;if ((image_fd = open(argv[1], O_RDONLY)) < 0) {err_sys("open error");}struct stat sbuf;if (fstat(image_fd, &sbuf) < 0) {err_sys("stat error");}unsigned char *jpeg_buffer = calloc(1, sbuf.st_size);read_image_from_file(image_fd, jpeg_buffer, sbuf.st_size);struct jpeg_decompress_struct   cinfo;struct jpeg_error_mgr           jerr;cinfo.err   =   jpeg_std_error(&jerr);jpeg_create_decompress(&cinfo);jpeg_mem_src(&cinfo, jpeg_buffer, sbuf.st_size);if (JPEG_HEADER_OK != jpeg_read_header(&cinfo, true)) {err_sys("read head error");}jpeg_start_decompress(&cinfo);struct image_info *image_info   =   calloc(1, sizeof(struct image_info));if (image_info == NULL) {err_sys("calloc error for image_info");}image_info->width       =   cinfo.output_width;image_info->height      =   cinfo.output_height;image_info->pixel_size  =   cinfo.output_components;int row_stride  =   image_info->width * image_info->pixel_size;size_t rgb_size =   row_stride * image_info->height;unsigned char *rgb_buffer = calloc(1, rgb_size);if (rgb_buffer == NULL) {err_sys("rgb_buffer error");}//循环读取解压后的数据，cinfo.output_scanline表示当前读取的行数while (cinfo.output_scanline < image_info->height) {unsigned char *buffer_array[1];buffer_array[0] =   rgb_buffer + cinfo.output_scanline * row_stride;jpeg_read_scanlines(&cinfo, buffer_array, 1);}jpeg_finish_decompress(&cinfo);jpeg_destroy_decompress(&cinfo);free(jpeg_buffer);int lcd_fd;if ((lcd_fd = open("/dev/fb0", O_RDWR)) < 0 ) {err_sys("open error");}   struct fb_var_screeninfo vinfo;ioctl(lcd_fd, FBIOGET_VSCREENINFO, &vinfo);size_t mem_size =   vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;unsigned char *lcdmem   =   mmap(0, mem_size, PROT_READ|PROT_WRITE, MAP_SHARED, lcd_fd, 0);if (lcdmem == MAP_FAILED) {err_sys("mmap error");}write_jpeg_to_lcd(lcdmem, rgb_buffer, &vinfo, image_info, 100, 100);free(rgb_buffer);munmap(lcdmem, mem_size);close(lcd_fd);close(image_fd);return EXIT_SUCCESS;
}

参考博客：http://blog.csdn.net/xipiaoyouzi/article/details/53257720