使用Boost.GIL将图像转换为“原始”字节

问题描述

我试图转向Boost GIL来替换一些类似的功能，我已经实现了它的可维护性生命的结束。

I'm trying to move towards Boost GIL to replace some similar functionality I've implemented that is reaching the end of its maintainable life.

我有现有的代码，使用 uint8_t * 可以使用24 BPP，8位RGB图像。我不能改变它，因为相同的接口用于暴露不同地方的图​​像（例如OpenGL缓冲区），并且已经有很多代码。

I have existing code that works with 24 BPP, 8bit RGB images using uint8_t*. I can't change that as the same interface is used to expose images from different places (e.g. OpenGL buffers) and there's already quite a lot of code.

尝试以小步骤使用GIL，首先读取一个文件，并将字节逐个字节复制到 std :: vector 中，我可以使用它来管理存储，但仍然通过使用& vector [0] 获得 uint8_t * 。

Therefore I'm trying to use GIL in small steps, starting by reading a file and copying the pixels byte by byte into a std::vector<uint8_t> which I can use to manage the storage, but still get a uint8_t* by using &vector[0].

这可以在现有接口的后面透明地删除，直到重构有意义。

This can be dropped in transparently behind the existing interfaces until it's at a point where refactoring makes sense.

我认为这应该是使用。

I thought this should be a simple case of using copy_pixels() with two appropriately constructed views.

我整理了一个简单完整的例子，说明了我通过查看文档和尝试操作来实现的总和：

I've put together a minimal, complete example that illustrates the sum of what I've manage to achieve by looking over the documents and trying things out:

#include <boost/gil/rgb.hpp>
#include <boost/gil/extension/io/png_dynamic_io.hpp>
#include <stdint.h>
#include <vector>

int main() {
  std::vector<uint8_t> storage;
  {
    using namespace boost::gil;
    rgb8_image_t img;
    png_read_image("test.png", img);

    // what should replace 3 here to be more "generic"?
    storage.resize(img.width()*img.height()*3);

    // doesn't work, the type of the images aren't compatible.
    copy_pixels(const_view(img),
                interleaved_view(img.width(), img.height(), &storage[0], 3*img.width()));
  }
}

我被困在哪里

这不编译：

Where I'm stuck

This doesn't compile:

error: cannot convert ‘const boost::gil::pixel<unsigned char, boost::gil::layout<boost::mpl::vector3<boost::gil::red_t, boost::gil::green_t, boost::gil::blue_t> > >’ to ‘unsigned char’ in assignment

这是相当不言自明的 - 不能自动转换为单个 unsigned char 。我以为我会尝试使用来解决这个问题，但是我看不到3：1的方法（即我有3 unsigned char s在输出为源图像中的每个像素）这些转换的问题。转换似乎更多针对颜色空间转换（例如RGB-> HSV）或换行。

Which is fairly self-explanatory - an RGB pixel can't be converted to a single unsigned char automatically. I thought I'd try using copy_and_convert_pixels() to fix this, but I can't see a way around the 3:1 (i.e. I have 3 unsigned chars in the output for every pixel in the source image) problem with these conversions. Conversion seems to be more aimed at colourspace conversions (e.g. RGB->HSV) or packing changes.

推荐答案

个别的颜色rgb8_pixel_t：

I would just push_back each color of the rgb8_pixel_t individually:

struct PixelInserter{
        std::vector<uint8_t>* storage;
        PixelInserter(std::vector<uint8_t>* s) : storage(s) {}
        void operator()(boost::gil::rgb8_pixel_t p) const {
                storage->push_back(boost::gil::at_c<0>(p));
                storage->push_back(boost::gil::at_c<1>(p));
                storage->push_back(boost::gil::at_c<2>(p));
        }
};

int main() {
  std::vector<uint8_t> storage;
  {
    using namespace boost::gil;
    rgb8_image_t img;
    png_read_image("test.png", img);
    storage.reserve(img.width() * img.height() * num_channels<rgb8_image_t>());
    for_each_pixel(const_view(img), PixelInserter(&storage));
  }
...
}

...我不是GIL的专家。

...but I'm not an expert on GIL either.

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