分类: LINUX
2010-08-20 23:10:36
http://wowocpp.blog.163.com/blog/static/124262780200911214567678/
http://blog.chinaunix.net/u2/84904/showart_1913883.html
apt-get install libjpeg62
编译的时候应该加上 -ljpeg
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define FB_DEV "/dev/fb0"
/***************** function declaration ******************/
void usage(char *msg);
unsigned short RGB888toRGB565(unsigned char red,
unsigned char green, unsigned char blue);
int fb_open(char *fb_device);
int fb_close(int fd);
int fb_stat(int fd, int *width, int *height, int *depth);
void *fb_mmap(int fd, unsigned int screensize);
int fb_munmap(void *start, size_t length);
int fb_pixel(void *fbmem, int width, int height,
int x, int y, unsigned short color);
/************ function implementation ********************/
int
main(int argc, char *argv[])
{
/*
* declaration for jpeg decompression
*/
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE *infile;
unsigned char *buffer;
/*
* declaration for framebuffer device
*/
int fbdev;
char *fb_device;
unsigned char *fbmem;
unsigned int screensize;
unsigned int fb_width;
unsigned int fb_height;
unsigned int fb_depth;
unsigned int x;
unsigned int y;
/*
* check auguments
*/
if (argc != 2) {
usage("insuffient auguments");
exit(-1);
}
/*
* open framebuffer device
*/
if ((fb_device = getenv("FRAMEBUFFER")) == NULL)
fb_device = FB_DEV;
fbdev = fb_open(fb_device);
/*
* get status of framebuffer device
*/
fb_stat(fbdev, &fb_width, &fb_height, &fb_depth);
/*
* map framebuffer device to shared memory
*/
screensize = fb_width * fb_height * fb_depth / 8;
fbmem = fb_mmap(fbdev, screensize);
/*
* open input jpeg file
*/
if ((infile = fopen(argv[1], "rb")) == NULL) {
fprintf(stderr, "open %s failed\n", argv[1]);
exit(-1);
}
/*
* init jpeg decompress object error handler
*/
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_decompress(&cinfo);
/*
* bind jpeg decompress object to infile
*/
jpeg_stdio_src(&cinfo, infile);
/*
* read jpeg header
*/
jpeg_read_header(&cinfo, TRUE);
/*
* decompress process.
* note: after jpeg_start_decompress() is called
* the dimension infomation will be known,
* so allocate memory buffer for scanline immediately
*/
jpeg_start_decompress(&cinfo);
if ((cinfo.output_width > fb_width) ||
(cinfo.output_height > fb_height)) {
printf("too large JPEG file,cannot display\n");
return (-1);
}
buffer = (unsigned char *) malloc(cinfo.output_width *
cinfo.output_components);
y = 0;
while (cinfo.output_scanline < cinfo.output_height) {
jpeg_read_scanlines(&cinfo, &buffer, 1);
if (fb_depth == 16) {
unsigned short color;
for (x = 0; x < cinfo.output_width; x++) {
color = RGB888toRGB565(buffer[x * 3],
buffer[x * 3 + 1], buffer[x * 3 + 2]);
fb_pixel(fbmem, fb_width, fb_height, x, y, color);
}
} else if (fb_depth == 24) {
memcpy((unsigned char *) fbmem + y * fb_width * 3,
buffer, cinfo.output_width * cinfo.output_components);
}
y++; // next scanline
}
/*
* finish decompress, destroy decompress object
*/
jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
/*
* release memory buffer
*/
free(buffer);
/*
* close jpeg inputing file
*/
fclose(infile);
/*
* unmap framebuffer's shared memory
*/
fb_munmap(fbmem, screensize);
/*
* close framebuffer device
*/
fb_close(fbdev);
return (0);
}
void
usage(char *msg)
{
fprintf(stderr, "%s\n", msg);
printf("Usage: fv some-jpeg-file.jpg\n");
}
/*
* convert 24bit RGB888 to 16bit RGB565 color format
*/
unsigned short
RGB888toRGB565(unsigned char red, unsigned char green, unsigned char blue)
{
unsigned short B = (blue >> 3) & 0x001F;
unsigned short G = ((green >> 2) << 5) & 0x07E0;
unsigned short R = ((red >> 3) << 11) & 0xF800;
return (unsigned short) (R | G | B);
}
/*
* open framebuffer device.
* return positive file descriptor if success,
* else return -1.
*/
int
fb_open(char *fb_device)
{
int fd;
if ((fd = open(fb_device, O_RDWR)) < 0) {
perror(__func__);
return (-1);
}
return (fd);
}
/*
* get framebuffer's width,height,and depth.
* return 0 if success, else return -1.
*/
int
fb_stat(int fd, int *width, int *height, int *depth)
{
struct fb_fix_screeninfo fb_finfo;
struct fb_var_screeninfo fb_vinfo;
if (ioctl(fd, FBIOGET_FSCREENINFO, &fb_finfo)) {
perror(__func__);
return (-1);
}
if (ioctl(fd, FBIOGET_VSCREENINFO, &fb_vinfo)) {
perror(__func__);
return (-1);
}
*width = fb_vinfo.xres;
*height = fb_vinfo.yres;
*depth = fb_vinfo.bits_per_pixel;
return (0);
}
/*
* map shared memory to framebuffer device.
* return maped memory if success,
* else return -1, as mmap dose.
*/
void *
fb_mmap(int fd, unsigned int screensize)
{
caddr_t fbmem;
if ((fbmem = mmap(0, screensize, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, 0)) == MAP_FAILED) {
perror(__func__);
return (void *) (-1);
}
return (fbmem);
}
/*
* unmap map memory for framebuffer device.
*/
int
fb_munmap(void *start, size_t length)
{
return (munmap(start, length));
}
/*
* close framebuffer device
*/
int
fb_close(int fd)
{
return (close(fd));
}
/*
* display a pixel on the framebuffer device.
* fbmem is the starting memory of framebuffer,
* width and height are dimension of framebuffer,
* x and y are the coordinates to display,
* color is the pixel's color value.
* return 0 if success, otherwise return -1.
*/
int
fb_pixel(void *fbmem, int width, int height,
int x, int y, unsigned short color)
{
if ((x > width) || (y > height))
return (-1);
unsigned short *dst = ((unsigned short *) fbmem + y * width + x);
*dst = color;
return 0;
}
libjpeg介绍:
libjpeg是一个被广泛使用的JPEG压缩/解压缩函数库,它能够读写JFIF格式的 JPEG图像文件,通常这类文件是以.jpg或者.jpeg为后缀名的。通过libjpeg库,应用程序可以每次从JPEG压缩图像中读取一个或多个扫描 线(scanline,所谓扫描线,是指由一行像素点构成的一条图像线条),而诸如颜色空间转换、降采样/增采样、颜色量化之类的工作则都由 libjpeg去完成了。
对于彩色图像,每个像素通常用三个分量表示,即R(Red)、G(Green)、B(Blue)三个分量,每个分量用一个字节表示,因此每个分量的取值范围从0到255;对于灰度图像,每个像素通常用一个分量表示,一个分量同样由一个字节表示,取值范围从0到255。
在libjpeg中,图像数据是以扫描线的形式存放的。每一条扫描线由一行像素点构成,像素点沿着扫描线从左到右依次排列。对于彩色图像,每个分量由三个字节组成,因此这三个字节以R、G、B的顺序构成扫描线上的一个像素点。一个典型的扫描线形式如下:
R,G,B,R,G,B,R,G,B,…
通过libjpeg解压出来的图像数据也是以扫描线的形式存放的。
在本文中,只涉及到JPEG的解压缩,因此只对libjpeg的解压过程进行说明,有关libjpeg的压缩过程和其它高级用法,请参考[3]。一般地,libjpeg的解压过程如下:
1、分配并初始化一个JPEG解压对象(本文中将JPEG解压对象命名为cinfo):
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
...
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_decompress(&cinfo);
2、指定要解压缩的图像文件:
FILE * infile;
...
if ((infile = fopen(filename, "rb")) == NULL) {
fprintf(stderr, "can't open %s\n", filename);
exit(1);
}
jpeg_stdio_src(&cinfo, infile);
3、调用jpeg_read_header()获取图像信息:
jpeg_read_header(&cinfo, TRUE);
4、这是一个可选步骤,用于设置JPEG解压缩对象cinfo的一些参数,本文可忽略;
5、调用jpeg_start_decompress()开始解压过程:
jpeg_start_decompress(&cinfo);
调用jpeg_start_decompress()函数之后,JPEG解压缩对象cinfo中的下面这几个字段将会比较有用:
l output_width 这是图像输出的宽度
l output_height 这是图像输出的高度
l output_components 每个像素的分量数,也即字节数
这是因为在调用jpeg_start_decompress()之后往往需要为解压后的扫描 线上的所有像素点分配存储空间,这个空间的大小可以通过output_width * output_componets确定,而要读取的扫描线的总数为output_height行。
6、读取一行或者多行扫描线数据并处理,通常的代码是这样的:
while (cinfo.output_scanline < cinfo.ouput_height) {
jpeg_read_scanlines();
/* deal with scanlines */
}
对扫描线的读取是按照从上到下的顺序进行的,也就是说图像最上方的扫描线最先被jpeg_read_scanlines()读入存储空间中,紧接着是第二个扫描线,最后是图像底边的扫描线被读入存储空间中。
7、调用jpeg_finish_decompress()完成解压过程:
jpeg_finish_decompress(&cinfo);
8、调用jpeg_destroy_decompress()释放JPEG解压对象cinfo:
jpeg_destroy_decompress(&cinfo);
以上就是通过libjpeg函数解压JPEG压缩图像的基本过程,由于本文不涉及libjpeg的高级特性和用法,因此,上面的介绍对于说明本文中要用到的libjpeg的功能已经足够了。
另外一个需要说明地方是:由于作者所用的Framebuffer设备的颜色深度为16位,颜 色格式为5-6-5格式——即R(红色)在16bit中占据高5位,G(绿色)在16bit中占据中间6位,B(蓝色)在16bit中占据低5位;而 libjpeg解压出来的图像数据为24位RGB格式,因此必须进行转换。对于24位的RGB,每个字节表示一个颜色分量,因此转换的方式为:对于R字 节,右移3位,对于G字节,右移2位,对于B字节,右移3位,然后将右移得到的值拼接起来,就得到了16位的颜色值。在后面的程序中,将把24位的颜色称 为RGB888,而把16位颜色值称为RGB565,这种命名方式可能不太规范,不过无论如何,在本文中就这样称呼了。另外,读者可能会想到,上面这种直 接将颜色分量的低位丢弃的方式不是会导致图像细节的丢失吗?比如,对于24位颜色的R字节,假如原来低3位的值在0~7之间均匀分布,转换之后,所有这低 3位的值全部都变成了0,这就是颜色细节的丢失。为了处理这个问题,可以采用误差扩散算法或者抖动算法来完成颜色转换。上面介绍的是最简单的转换方式—— 而且事实表明,这样做得到的结果并不差。
for(i=0;i<16;i+=2)
{
bits=ch[i/2];
for(j=0;j<16;j+=2,bits<<=1)
if(bits&0x80)
{
location1 = (x+j) * (vinfo.bits_per_pixel / 8) + (y+i) * finfo.line_length;
location2 = (x+j+1) * (vinfo.bits_per_pixel / 8) + (y+i) * finfo.line_length;
location3 = (x+j) * (vinfo.bits_per_pixel / 8) + (y+i+1) * finfo.line_length;
location4 = (x+j+1) * (vinfo.bits_per_pixel / 8) + (y+i+1) * finfo.line_length;
*(unsigned short*)(fbp + location1) =0x00ff; /* 蓝色的色深 */ /*直接赋值来改变屏幕上某点的颜色*/
*(unsigned short*)(fbp + location2) =0x00ff; /* 蓝色的色深 */ /*直接赋值来改变屏幕上某点的颜色*/
*(unsigned short*)(fbp + location3) =0x00ff; /* 蓝色的色深 */ /*直接赋值来改变屏幕上某点的颜色*/
*(unsigned short*)(fbp + location4) =0x00ff; /* 蓝色的色深 */ /*直接赋值来改变屏幕上某点的颜色*/
}
}