将 BGR 图像转换为 jpeg 格式的 base64 字符串

Question

我有以OpenCV约定表示的彩色图像，其中每个像素都以BGR顺序一行又一行地表示为unsigned char：

const int BGR = 3;
const int rows= 256;
const int cols = 512;
unsigned char rawIm[BGR * rows *cols] = {'g', 't', 'y', // lots of chars.....}

我想将此流转换为表示相应 jpeg 图像的 base64 字符串，而无需实际将图像写入磁盘，只是"纯"字节转换。 如何在C++中做到这一点？

Answer 1

对于图像到jpeg部分，您可以使用toojpeg，它比libjpeg更容易使用。 https://create.stephan-brumme.com/toojpeg/

但是您必须先将 BGR 反转为 RGB，因为 toojpeg 还不支持 BGR。

下面是一个示例：

#include <vector>
#include <string>
#include <iostream>
#include "toojpeg.h"
std::vector<unsigned char> jpeg_data;
void myOutput(unsigned char byte) {
jpeg_data.push_back(byte);
}
int main() {
const auto width = 800;
const auto height = 600;
const auto bytesPerPixel = 3;
unsigned char bgr_data[width * height * bytesPerPixel];
// put some sample data in bgr_data, just for the example
for (unsigned i = 0; i < sizeof(bgr_data); i += 3) {
bgr_data[i]     = i / width;
bgr_data[i + 1] = i / width * 2;
bgr_data[i + 2] = i / width * 3;
}
// convert BGR to RGB
unsigned char rgb_data[sizeof(bgr_data)];
for (unsigned i = 0; i < sizeof(bgr_data); i += 3) {
rgb_data[i]     = bgr_data[i + 2];
rgb_data[i + 1] = bgr_data[i + 1];
rgb_data[i + 2] = bgr_data[i];
}
// convert the RGB data to jpeg
bool isRGB = true;
const auto quality = 90;
const bool downsample = false;
const char* comment = "example image";
bool result_ok = TooJpeg::writeJpeg(myOutput, rgb_data, width, height, isRGB, quality, downsample, comment);
if (result_ok) {
// jpeg_data now contains jpeg-encoded image, which can be encoded as base 64
}
return 0;
}