libjpeg用法linux压缩,libjpeg学习1：简单使用示例

最新推荐文章于 2024-04-08 08:07:48 发布

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最新推荐文章于 2024-04-08 08:07:48 发布

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文章标签： libjpeg用法linux压缩

本文提供了一套完整的JPEG图片处理方法，包括读取并解压JPEG格式的图片到内存中，以及从内存中写入JPEG格式的图片。文中详细展示了如何使用libjpeg库进行JPEG图片的解码和编码。

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#include

// jpeg库头文件必须放到stdio.h后面

#include "libjpeg/include/jpeglib.h"

#include "libjpeg/include/jerror.h"

typedef struct my_error_mgr * my_error_ptr;

void my_error_exit (j_common_ptr cinfo)

{

my_error_ptr myerr = (my_error_ptr) cinfo->err;

(*cinfo->err->output_message) (cinfo);

longjmp(myerr->setjmp_buffer, 1);

}

// 读取JPG图片数据，并解压到内存中，*rgb_buffer需要自行释放

int read_jpeg_file(const char* jpeg_file, unsigned char** rgb_buffer, int* size, int* width, int* height)

{

struct jpeg_decompress_struct cinfo;

struct my_error_mgr jerr;

FILE* fp;

JSAMPARRAY buffer;

int row_stride = 0;

unsigned char* tmp_buffer = NULL;

int rgb_size;

fp = fopen(jpeg_file, "rb");

if (fp == NULL)

{

printf("open file %s failed.\n", jpeg_file);

return -1;

}

cinfo.err = jpeg_std_error(&jerr.pub);

jerr.pub.error_exit = my_error_exit;

if (setjmp(jerr.setjmp_buffer))

{

jpeg_destroy_decompress(&cinfo);

fclose(fp);

return -1;

}

jpeg_create_decompress(&cinfo);

jpeg_stdio_src(&cinfo, fp);

jpeg_read_header(&cinfo, TRUE);

//cinfo.out_color_space = JCS_RGB; //JCS_YCbCr; // 设置输出格式

jpeg_start_decompress(&cinfo);

row_stride = cinfo.output_width * cinfo.output_components;

*width = cinfo.output_width;

*height = cinfo.output_height;

rgb_size = row_stride * cinfo.output_height; // 总大小

*size = rgb_size;

buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

*rgb_buffer = (unsigned char *)malloc(sizeof(char) * rgb_size); // 分配总内存

printf("debug--:\nrgb_size: %d, size: %d w: %d h: %d row_stride: %d \n", rgb_size,

cinfo.image_width*cinfo.image_height*3,

cinfo.image_width,

cinfo.image_height,

row_stride);

tmp_buffer = *rgb_buffer;

while (cinfo.output_scanline < cinfo.output_height) // 解压每一行

{

jpeg_read_scanlines(&cinfo, buffer, 1);

// 复制到内存

memcpy(tmp_buffer, buffer[0], row_stride);

tmp_buffer += row_stride;

}

jpeg_finish_decompress(&cinfo);

jpeg_destroy_decompress(&cinfo);

fclose(fp);

return 0;

}

int write_jpeg_file(const char* jpeg_file, unsigned char* rgb_buffer, int width, int height, int quality)

{

struct jpeg_compress_struct cinfo;

struct jpeg_error_mgr jerr;

int row_stride = 0;

FILE* fp = NULL;

JSAMPROW row_pointer[1];

cinfo.err = jpeg_std_error(&jerr);

jpeg_create_compress(&cinfo);

fp = fopen(jpeg_file, "wb");

if (fp == NULL)

{

printf("open file %s failed.\n", jpeg_file);

return -1;

}

jpeg_stdio_dest(&cinfo, fp);

cinfo.image_width = width;

cinfo.image_height = height;

cinfo.input_components = 3;

cinfo.in_color_space = JCS_RGB;

jpeg_set_defaults(&cinfo);

jpeg_set_quality(&cinfo, quality, 1); // todo 1 == true

jpeg_start_compress(&cinfo, TRUE);

row_stride = width * cinfo.input_components;

while (cinfo.next_scanline < cinfo.image_height)

{

row_pointer[0] = &rgb_buffer[cinfo.next_scanline * row_stride];

jpeg_write_scanlines(&cinfo, row_pointer, 1);

}

jpeg_finish_compress(&cinfo);

jpeg_destroy_compress(&cinfo);

fclose(fp);

return 0;

}