JPEG库的移植（arm平台）
目录介绍
图解
头文件及全局变量
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
/*
* Include file for users of JPEG library.
* You will need to have included system headers that define at least
* the typedefs FILE and size_t before you can include jpeglib.h.
* (stdio.h is sufficient on ANSI-conforming systems.)
* You may also wish to include "jerror.h".
*/
#include "jpeglib.h"
#pragma pack(1)
typedef struct tagBmpFileHeader // 文件头
{
unsigned short bfType; // 标识该文件为bmp文件,判断文件是否为bmp文件，即用该值与"0x4d42"比较是否相等即可，0x4d42 = 19778
unsigned long bfSize; // 位图文件大小，包括这14个字节。
unsigned short bfReserved1; // 预保留位，暂不用。
unsigned short bfReserved2; // 预保留位，暂不用。
unsigned long bfOffBits; // 图像数据区的起始位置
} BmpFileHeader; // 14字节:short2个,long4个
typedef struct tagBmpInfoHeader // 信息头
{
unsigned long biSize; // 本结构的长度，为40个字节。
long biWidth; // 宽度
long biHeight; // 高度
unsigned short biPlanes; // 目标设备的级别，必须是1。
unsigned short biBitCount; // 每个像素所占的位数（bit），其值必须为1（黑白图像）、4（16色图）、8（256色）、24（真彩色图），新的BMP格式支持32位色。
unsigned longbiCompression; // 压缩方式，有效的值为BI_RGB（未经压缩）、BI_RLE8、BI_RLE4、BI_BITFILEDS（均为Windows定义常量）。
unsigned longbiSizeImage; // 图像区数据大小，即实际的位图数据占用的字节数
long biXPelsPerMeter; // 水平分辨率，像素每米
long biYPelsPerMeter; // 垂直分辨率，单位是像素/米
unsigned long biClrUsed; // 位图实际用到的颜色数，如果该值为零，则用到的颜色数为2的biBitCount次幂。
unsigned short biClrImportant; // 位图显示过程，重要的颜色数；0--所有都重要
} BmpInfoHeader; // 40字节
#pragma pack()
int *lcd_mp;
1、图片显示
int read_JPEG_file(char *filename,
int start_x,
int start_y)
{
/* This struct contains the JPEG decompression parameters and pointers to
* working space (which is allocated as needed by the JPEG library).
*/
struct jpeg_decompress_struct cinfo;
/* We use our private extension JPEG error handler.
* Note that this struct must live as long as the main JPEG parameter
* struct, to avoid dangling-pointer problems.
*/
struct jpeg_error_mgr jerr;
/* More stuff */
FILE *infile; /* source file */
unsigned char *buffer; /* Output row buffer */
int row_stride; /* physical row width in output buffer */
/* In this example we want to open the input file before doing anything else,
* so that the setjmp() error recovery below can assume the file is open.
* VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
* requires it in order to read binary files.
*/
if ((infile = fopen(filename, "rb")) == NULL)
{
fprintf(stderr, "can't open %s\n", filename);
return 0;
}
/* Step 1: allocate and initialize JPEG decompression object */
/* We set up the normal JPEG error routines, then override error_exit. */
cinfo.err = jpeg_std_error(&jerr);
/* Now we can initialize the JPEG decompression object. */
jpeg_create_decompress(&cinfo);
/* Step 2: specify data source (eg, a file) */
jpeg_stdio_src(&cinfo, infile);
/* Step 3: read file parameters with jpeg_read_header() */
(void)jpeg_read_header(&cinfo, TRUE);
/* We can ignore the return value from jpeg_read_header since
* (a) suspension is not possible with the stdio data source, and
* (b) we passed TRUE to reject a tables-only JPEG file as an error.
* See libjpeg.txt for more info.
*/
/* Step 4: set parameters for decompression */
/* In this example, we don't need to change any of the defaults set by
* jpeg_read_header(), so we do nothing here.
*/
/* Step 5: Start decompressor */
(void)jpeg_start_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
/* We may need to do some setup of our own at this point before reading
* the data. After jpeg_start_decompress() we have the correct scaled
* output image dimensions available, as well as the output colormap
* if we asked for color quantization.
* In this example, we need to make an output work buffer of the right size.
*/
/* JSAMPLEs per row in output buffer */
row_stride = cinfo.output_width * cinfo.output_components; // 计算一行的大小
/* Make a one-row-high sample array that will go away when done with image */
buffer = calloc(1, row_stride);
/* Step 6: while (scan lines remain to be read) */
/* jpeg_read_scanlines(...); */
/* Here we use the library's state variable cinfo.output_scanline as the
* loop counter, so that we don't have to keep track ourselves.
*/
int data = 0;
while (cinfo.output_scanline < cinfo.output_height)
{
/* jpeg_read_scanlines expects an array of pointers to scanlines.
* Here the array is only one element long, but you could ask for
* more than one scanline at a time if that's more convenient.
*/
(void)jpeg_read_scanlines(&cinfo, &buffer, 1); // 从上到下，从左到右 RGB RGB RGB RGB
for (int i = 0; i < cinfo.output_width; ++i) // 012 345
{
data |= buffer[3 * i] << 16; // R
data |= buffer[3 * i + 1] << 8; // G
data |= buffer[3 * i + 2]; // B
// 把像素点写入到LCD的指定位置
lcd_mp[800 * start_y + start_x + 800 * (cinfo.output_scanline - 1) + i] = data;
data = 0;
}
}
/* Step 7: Finish decompression */
(void)jpeg_finish_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
/* Step 8: Release JPEG decompression object */
/* This is an important step since it will release a good deal of memory. */
jpeg_destroy_decompress(&cinfo);
/* After finish_decompress, we can close the input file.
* Here we postpone it until after no more JPEG errors are possible,
* so as to simplify the setjmp error logic above. (Actually, I don't
* think that jpeg_destroy can do an error exit, but why assume anything...)
*/
fclose(infile);
/* At this point you may want to check to see whether any corrupt-data
* warnings occurred (test whether jerr.pub.num_warnings is nonzero).
*/
/* And we're done! */
return 1;
}
2、其他图片压缩到jpg图片
write_JPEG_file(char *filename,
int image_width,
int image_height,
unsigned char *image_buffer)
{
/* This struct contains the JPEG compression parameters and pointers to
* working space (which is allocated as needed by the JPEG library).
* It is possible to have several such structures, representing multiple
* compression/decompression processes, in existence at once. We refer
* to any one struct (and its associated working data) as a "JPEG object".
*/
/* Step 1*/
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
/* More stuff */
FILE *outfile; // 文档指针
unsigned char *row_pointer[1]; // 行指针
int row_stride;
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
/* Step 2: specify data destination (eg, a file) */
if ((outfile = fopen(filename, "wb")) == NULL)
{
fprintf(stderr, "can't open %s\n", filename);
exit(1);
}
jpeg_stdio_dest(&cinfo, outfile);
/* Step 3: set parameters for compression */
// 宽高
cinfo.image_width = image_width; /* image width and height, in pixels */
cinfo.image_height = image_height;
// 色深
cinfo.input_components = 3; /* # of color components per pixel */
// 头文件内东西
cinfo.in_color_space = JCS_RGB; /* colorspace of input image */
jpeg_set_defaults(&cinfo);
/* Step 4: Start compressor */
/* TRUE ensures that we will write a complete interchange-JPEG file.
* Pass TRUE unless you are very sure of what you're doing.
*/
jpeg_start_compress(&cinfo, TRUE);
/* Step 5: while (scan lines remain to be written) */
/* jpeg_write_scanlines(...); */
/* Here we use the library's state variable cinfo.next_scanline as the
* loop counter, so that we don't have to keep track ourselves.
* To keep things simple, we pass one scanline per call; you can pass
* more if you wish, though.
*/
row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */
while (cinfo.next_scanline < cinfo.image_height)
{
/* jpeg_write_scanlines expects an array of pointers to scanlines.
* Here the array is only one element long, but you could pass
* more than one scanline at a time if that's more convenient.
*/
row_pointer[0] = &image_buffer[cinfo.next_scanline * row_stride];
(void)jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
/* Step 6: Finish compression */
jpeg_finish_compress(&cinfo);
/* After finish_compress, we can close the output file. */
fclose(outfile);
/* Step 7: release JPEG compression object */
/* This is an important step since it will release a good deal of memory. */
jpeg_destroy_compress(&cinfo);
/* And we're done! */
}
3、主函数及验证程序
int main(int argc,
char const *argv[])
{
// 1.打开LCD open
int lcd_fd = open("/dev/fb0", O_RDWR);
// 2.对LCD进行内存映射 mmap
lcd_mp = (int *)mmap(NULL,
800 * 480 * 4,
PROT_READ | PROT_WRITE, MAP_SHARED,
lcd_fd, 0);
// 1.打开待显示的BMP图像 fopen
FILE *bmp_fp1 = fopen("jojo.bmp", "rb");
BmpFileHeader headfile1;
BmpInfoHeader headerinfo1;
fseek(bmp_fp1, 0, SEEK_SET);
fread(&headfile1, 1, 14, bmp_fp1); // 读取14字节
fread(&headerinfo1, 1, 40, bmp_fp1); // 读取40字节
int H1 = headerinfo1.biHeight *
headerinfo1.biWidth *
headerinfo1.biBitCount / 8;
// 3.读取BMP图*片的颜色分量 800*480*3
char bmp_buf1[800 * 480 * 3];
fread(bmp_buf1, 1, 800 * 480 * 3, bmp_fp1);
write_JPEG_file("1.jpg",
800,
480,
bmp_buf1);
// 3.显示一张jpg
read_JPEG_file("1.jpg", 0, 0);
return 0;
}
输出结果
原图
输出图
