怎么封装libjpeg格式转换的方法
时间: 2024-05-09 16:21:11 浏览: 13
假设你要封装一个将BMP格式转换为JPEG格式的方法,具体步骤如下:
1. 安装libjpeg库并包含相关头文件
```c
#include <stdio.h>
#include <jpeglib.h>
```
2. 定义一个函数,接收BMP图像数据和图像属性参数,返回JPEG图像数据和大小
```c
unsigned char* BMPtoJPEG(unsigned char* bmp_data, int width, int height, int channels, int* jpeg_size);
```
3. 在函数中定义libjpeg所需的结构体和变量
```c
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
JSAMPROW row_pointer[1];
unsigned char* jpeg_data = NULL;
unsigned long jpeg_size = 0;
```
4. 初始化libjpeg结构体和错误处理器
```c
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
```
5. 设置输出JPEG文件的属性,如图像宽度、高度、颜色分量等
```c
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = channels;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults(&cinfo);
```
6. 计算输出JPEG文件的大小并分配内存
```c
jpeg_data = (unsigned char*)malloc(width * height * channels * sizeof(unsigned char));
jpeg_mem_dest(&cinfo, &jpeg_data, &jpeg_size);
```
7. 开始压缩图像数据并写入输出JPEG文件
```c
jpeg_start_compress(&cinfo, TRUE);
while (cinfo.next_scanline < cinfo.image_height) {
row_pointer[0] = &bmp_data[cinfo.next_scanline * width * channels];
jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_finish_compress(&cinfo);
```
8. 释放资源并返回输出JPEG文件数据和大小
```c
jpeg_destroy_compress(&cinfo);
*jpeg_size = (int)jpeg_size;
return jpeg_data;
```
完整代码示例:
```c
#include <stdio.h>
#include <jpeglib.h>
unsigned char* BMPtoJPEG(unsigned char* bmp_data, int width, int height, int channels, int* jpeg_size)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
JSAMPROW row_pointer[1];
unsigned char* jpeg_data = NULL;
unsigned long jpeg_size = 0;
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = channels;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_data = (unsigned char*)malloc(width * height * channels * sizeof(unsigned char));
jpeg_mem_dest(&cinfo, &jpeg_data, &jpeg_size);
jpeg_start_compress(&cinfo, TRUE);
while (cinfo.next_scanline < cinfo.image_height) {
row_pointer[0] = &bmp_data[cinfo.next_scanline * width * channels];
jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_finish_compress(&cinfo);
jpeg_destroy_compress(&cinfo);
*jpeg_size = (int)jpeg_size;
return jpeg_data;
}
```
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