如何从System.Drawing.Bitmap转换为灰度，然后转换为双精度数组（Double [，]），然后再转换为灰度位图？ [英] How to convert from System.Drawing.Bitmap to grayscale, then to array of doubles (Double[,]), then back to grayscale Bitmap?

问题描述

我需要在照片中执行一些数学运算，为此我需要图像的浮点灰度版本（可能来自JPG，PNG或具有各种颜色深度的BMP文件）。

I need to perform some mathematical operations in photographs, and for that I need the floating point grayscale version of an image (which might come from JPG, PNG or BMP files with various colordepths).

我以前在Python中使用 PIL 和 scipy.ndimage 来做到这一点，它是非常简单地用 PIL 转换为灰度，然后转换为带有 numpy 的浮点数数组，但现在我需要在C＃中做类似的事情，我很困惑如何这样做。

I used to do that in Python using PIL and scipy.ndimage, and it was very straightforward to convert to grayscale with PIL and then to an array of floating-point numbers with numpy, but now I need to do something similar in C#, and I'm confused how to do so.

我读过这个非常好的教程，这似乎是一个反复出现的参考，但只涵盖了转换为灰度部分，我不知道如何从Bitmap获取双打数组，然后（在某个时刻）将其转换回System.Drawing.Bitmap以供查看。

I have read this very nice tutorial, that seems to be a recurring reference, but that only covers the "convert to grayscale" part, I am not sure how to get an array of doubles from a Bitmap, and then (at some moment) to convert it back to System.Drawing.Bitmap for viewing.

推荐答案

决赛代码，主要基于从评论中提取的提示，特别是 LockBits 部分（这里的博客文章）以及R，G和B值之间的感知平衡（这里不是最重要的，但需要了解的事情）：

The final code, based mostly in tips taken from the comments, specifically the LockBits part (blog post here) and the perceptual balancing between R, G and B values (not paramount here, but something to know about):

    private double[,] TransformaImagemEmArray(System.Drawing.Bitmap imagem) {
        // Transforma a imagem de entrada em um array de doubles
        // com os valores grayscale da imagem

        BitmapData bitmap_data = imagem.LockBits(new System.Drawing.Rectangle(0,0,_foto_franjas_original.Width,_foto_franjas_original.Height),
                                            ImageLockMode.ReadOnly, _foto_franjas_original.PixelFormat);

        int pixelsize = System.Drawing.Image.GetPixelFormatSize(bitmap_data.PixelFormat)/8;

        IntPtr pointer = bitmap_data.Scan0;
        int nbytes = bitmap_data.Height * bitmap_data.Stride;
        byte[] imagebytes = new byte[nbytes];
        System.Runtime.InteropServices.Marshal.Copy(pointer, imagebytes, 0, nbytes);

        double red;
        double green;
        double blue;
        double gray;

        var _grayscale_array = new Double[bitmap_data.Height, bitmap_data.Width];

        if (pixelsize >= 3 ) {
            for (int I = 0; I < bitmap_data.Height; I++) {
                for (int J = 0; J < bitmap_data.Width; J++ ) {
                    int position = (I * bitmap_data.Stride) + (J * pixelsize);
                    blue = imagebytes[position];
                    green = imagebytes[position + 1];
                    red = imagebytes[position + 2];
                    gray = 0.299 * red + 0.587 * green + 0.114 * blue;
                    _grayscale_array[I,J] = gray;
                }
            }
        }

        _foto_franjas_original.UnlockBits(bitmap_data);

        return _grayscale_array;
    }

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