準備工作同上篇一緻。JPEG壓縮
基于libjpeg中的example.c進行擴充編寫
解碼原理及實作後續會進行介紹
代碼部分：
#include <afxwin.h>
#include <setjmp.h>
extern "C" {
#include "jpeglib.h"
#include "jmorecfg.h"
#include "jconfig.h"
}
struct my_error_mgr {
struct jpeg_error_mgr pub; /* "public" fields */
jmp_buf setjmp_buffer; /* for return to caller */
};
typedef struct /**** BMP file header structure ****/
{
unsigned int bfSize; /* Size of file */
unsigned short bfReserved1; /* Reserved */
unsigned short bfReserved2; /* ... */
unsigned int bfOffBits; /* Offset to bitmap data */
} BITMAPFILEHEADER1;
typedef struct /**** BMP file info structure ****/
{
unsigned int biSize; /* Size of info header */
int biWidth; /* Width of image */
int biHeight; /* Height of image */
unsigned short biPlanes; /* Number of color planes */
unsigned short biBitCount; /* Number of bits per pixel */
unsigned int biCompression; /* Type of compression to use */
unsigned int biSizeImage; /* Size of image data */
int biXPelsPerMeter; /* X pixels per meter */
int biYPelsPerMeter; /* Y pixels per meter */
unsigned int biClrUsed; /* Number of colors used */
unsigned int biClrImportant; /* Number of important colors */
} BITMAPINFOHEADER1;
typedef struct tagRGBQUAD1{
BYTE rgbBlue;//藍色的亮度（值範圍為0-255)
BYTE rgbGreen;//綠色的亮度（值範圍為0-255)
BYTE rgbRed;//紅色的亮度（值範圍為0-255)
BYTE rgbReserved;//保留，必須為0
}RGBQUAD1;
typedef struct my_error_mgr * my_error_ptr;
METHODDEF(void)
my_error_exit(j_common_ptr cinfo)
{
/* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
my_error_ptr myerr = (my_error_ptr)cinfo->err;
/* Always display the message. */
/* We could postpone this until after returning, if we chose. */
(*cinfo->err->output_message) (cinfo);
/* Return control to the setjmp point */
longjmp(myerr->setjmp_buffer, 1);
}
static void _RGB2BGR(unsigned char *picInfo, int width, int height, int depth)
{
unsigned char* pRGBData = picInfo;
unsigned bufferLen = width*height*depth;
unsigned char tmpData;
while (bufferLen)
{
memcpy(&tmpData, pRGBData, 1);
memcpy(pRGBData, pRGBData + 2, 1);
memcpy(pRGBData + 2, &tmpData, 1);
pRGBData += 3;
bufferLen -= 3;
}
return;
}
void MySaveBmp(const char *filename, unsigned char *rgbbuf, int width, int height, unsigned int bit, unsigned int a, unsigned int bit_comp)
{
BITMAPFILEHEADER1 bfh;
BITMAPINFOHEADER1 bih;
/* Magic number for file. It does not fit in the header structure due to alignment requirements, so put it outside */
unsigned short bfType = 0x4d42;
//bfh.bfType = 0x4d42;
bfh.bfReserved1 = 0;
bfh.bfReserved2 = 0;
bfh.bfSize = 2 + sizeof(BITMAPFILEHEADER1) + sizeof(BITMAPINFOHEADER1) + width*height * bit;
bfh.bfOffBits = 0x36;
bih.biSize = sizeof(BITMAPINFOHEADER1);
bih.biWidth = width;
bih.biHeight = -height;
bih.biPlanes = 1;
bih.biBitCount = bit * 8;//
bih.biCompression = bit_comp;//說明圖像資料壓縮類型
bih.biSizeImage = 0;
bih.biXPelsPerMeter = 5000;
bih.biYPelsPerMeter = 5000;
bih.biClrUsed = 0;
bih.biClrImportant = 0;
DWORD nRGBMask[3];
nRGBMask[0] = 0xf800;
nRGBMask[1] = 0x07e0;
nRGBMask[2] = 0x001f;
FILE *file = fopen(filename, "wb");
if (!file)
{
printf("Could not write file\n");
return;
}
/*Write headers*/
fwrite(&bfType, sizeof(bfType), 1, file);
fwrite(&bfh, sizeof(bfh), 1, file);
fwrite(&bih, sizeof(bih), 1, file);
if (a == 1)
fwrite(nRGBMask, sizeof(nRGBMask), 1, file);
fwrite(rgbbuf, width*height * bit, 1, file);
fclose(file);
}
int read_JPEG_file(char * filename)
{
/* 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 my_error_mgr jerr;
/* More stuff */
FILE * infile; /* source file */
JSAMPARRAY 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.pub);
jerr.pub.error_exit = my_error_exit;
/* Establish the setjmp return context for my_error_exit to use. */
if (setjmp(jerr.setjmp_buffer)) {
/* If we get here, the JPEG code has signaled an error.
* We need to clean up the JPEG object, close the input file, and return.
*/
jpeg_destroy_decompress(&cinfo);
fclose(infile);
return 0;
}
/* 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;
/* Make a one-row-high sample array that will go away when done with image */
buffer = (*cinfo.mem->alloc_sarray)
((j_common_ptr)&cinfo, JPOOL_IMAGE, row_stride, 1);
/* 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.
*/
unsigned long width = cinfo.output_width;//圖像寬度
unsigned long height = cinfo.output_height;//圖像高度
unsigned short depth = cinfo.output_components;//圖像深度
unsigned char *src_buff;//用于存取解碼之後的位圖資料(RGB格式)
src_buff = (unsigned char *)malloc(width * height * depth);//配置設定位圖資料空間
memset(src_buff, 0, sizeof(unsigned char) * width * height * depth);//清0
unsigned char *point = src_buff;
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);
/* Assume put_scanline_someplace wants a pointer and sample count. */
//put_scanline_someplace(buffer[0], row_stride);
memcpy(point, *buffer, width*depth); //将buffer中的資料逐行給src_buff
point += width * depth; //指針偏移一行
}
_RGB2BGR(src_buff, width, height, depth);
MySaveBmp("test.bmp", src_buff, width, height, 3, 0, 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;
}
int main(int argc, char* argv[])
{
read_JPEG_file("3.jpg");
getchar();
return 0;
}
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