JPEG庫的移植（arm平臺）

• JPEG庫的移植（arm平臺）
  • 介紹
  • 頭文件及全局變數
  • 1、圖片顯示
  • 2、其他圖片壓縮到jpg圖片
  • 3、主函數及驗證程式
    • 輸出結果

介紹

圖解

頭文件及全局變數

#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 // 文件頭
{
  unsigned short bfType;      // 標識該文件為bmp文件,判斷文件是否為bmp文件，即用該值與"0x4d42"比較是否相等即可，0x4d42 = 19778
  unsigned long bfSize;       // 點陣圖文件大小，包括這14個位元組。
  unsigned short bfReserved1; // 預保留位，暫不用。
  unsigned short bfReserved2; // 預保留位，暫不用。
  unsigned long bfOffBits;    // 圖像數據區的起始位置
} BmpFileHeader;              // 14位元組:short2個,long4個

typedef struct tagBmpInfoHeader // 信息頭
{
  unsigned long biSize;          // 本結構的長度，為40個位元組。
  long biWidth;                  // 寬度
  long biHeight;                 // 高度
  unsigned short biPlanes;       // 目標設備的級別，必須是1。
  unsigned short biBitCount;     // 每個像素所占的位數（bit），其值必須為1（黑白圖像）、4（16色圖）、8（256色）、24（真彩色圖），新的BMP格式支持32位色。
  unsigned longbiCompression;    // 壓縮方式，有效的值為BI_RGB（未經壓縮）、BI_RLE8、BI_RLE4、BI_BITFILEDS（均為Windows定義常量）。
  unsigned longbiSizeImage;      // 圖像區數據大小，即實際的點陣圖數據占用的位元組數
  long biXPelsPerMeter;          // 水平解析度，像素每米
  long biYPelsPerMeter;          // 垂直解析度，單位是像素/米
  unsigned long biClrUsed;       // 點陣圖實際用到的顏色數，如果該值為零，則用到的顏色數為2的biBitCount次冪。
  unsigned short biClrImportant; // 點陣圖顯示過程，重要的顏色數；0--所有都重要
} BmpInfoHeader;                 // 40位元組
#pragma pack()

int *lcd_mp;

1、圖片顯示

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; // 計算一行的大小

  /* 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); // 從上到下，從左到右  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

      // 把像素點寫入到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、其他圖片壓縮到jpg圖片

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;                 // 文檔指針
  unsigned char *row_pointer[1]; // 行指針
  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 */

  // 寬高
  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 */
  // 頭文件內東西
  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、主函數及驗證程式

int main(int argc,
         char const *argv[])
{
  // 1.打開LCD   open
  int lcd_fd = open("/dev/fb0", O_RDWR);

  // 2.對LCD進行記憶體映射  mmap
  lcd_mp = (int *)mmap(NULL,
                       800 * 480 * 4,
                       PROT_READ | PROT_WRITE, MAP_SHARED,
                       lcd_fd, 0);

  // 1.打開待顯示的BMP圖像  fopen
  FILE *bmp_fp1 = fopen("jojo.bmp", "rb");
  BmpFileHeader headfile1;
  BmpInfoHeader headerinfo1;
  fseek(bmp_fp1, 0, SEEK_SET);
  fread(&headfile1, 1, 14, bmp_fp1);   // 讀取14位元組
  fread(&headerinfo1, 1, 40, bmp_fp1); // 讀取40位元組

  int H1 = headerinfo1.biHeight *
           headerinfo1.biWidth *
           headerinfo1.biBitCount / 8;
  // 3.讀取BMP圖*片的顏色分量  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.顯示一張jpg
  read_JPEG_file("1.jpg", 0, 0);

  return 0;
}

輸出結果

原圖

輸出圖