C# 无法显示具有正确颜色映射的 RAW16 灰度图像

Question

修改此链接中提供的代码:

Original code

我是这样写的:

    private void btnLoad_Click(object sender, EventArgs e)
    {
        if (System.IO.File.Exists(txtPicture.Text))
        {
            byte[] _data = System.IO.File.ReadAllBytes(txtPicture.Text);

            var _rgbData = Convert16BitGrayScaleToRgb16(_data, 160, 120);
            var _bmp = CreateBitmapFromBytes(_rgbData, 160, 120);

            pbFrame.Image = _bmp;
        }
    }

    private static void Convert16bitGSToRGB(UInt16 color, out byte red, out byte green, out byte blue)
    {
        red = (byte)(color & 0x31);
        green = (byte)((color & 0x7E0) >> 5);
        blue = (byte)((color & 0xF800) >> 11);
    }

    private static byte[] Convert16BitGrayScaleToRgb48(byte[] inBuffer, int width, int height)
    {
        int inBytesPerPixel = 2;
        int outBytesPerPixel = 6;

        byte[] outBuffer = new byte[width * height * outBytesPerPixel];
        int inStride = width * inBytesPerPixel;
        int outStride = width * outBytesPerPixel;

        // Step through the image by row
        for (int y = 0; y < height; y++)
        {
            // Step through the image by column
            for (int x = 0; x < width; x++)
            {
                // Get inbuffer index and outbuffer index
                int inIndex = (y * inStride) + (x * inBytesPerPixel);
                int outIndex = (y * outStride) + (x * outBytesPerPixel);

                byte hibyte = inBuffer[inIndex + 1];
                byte lobyte = inBuffer[inIndex];

                //R
                outBuffer[outIndex] = lobyte;
                outBuffer[outIndex + 1] = hibyte;

                //G
                outBuffer[outIndex + 2] = lobyte;
                outBuffer[outIndex + 3] = hibyte;

                //B
                outBuffer[outIndex + 4] = lobyte;
                outBuffer[outIndex + 5] = hibyte;
            }
        }
        return outBuffer;
    }

    private static byte[] Convert16BitGrayScaleToRgb16(byte[] inBuffer, int width, int height)
    {
        int inBytesPerPixel = 2;
        int outBytesPerPixel = 2;

        byte[] outBuffer = new byte[width * height * outBytesPerPixel];
        int inStride = width * inBytesPerPixel;
        int outStride = width * outBytesPerPixel;

        // Step through the image by row
        for (int y = 0; y < height; y++)
        {
            // Step through the image by column
            for (int x = 0; x < width; x++)
            {
                // Get inbuffer index and outbuffer index
                int inIndex = (y * inStride) + (x * inBytesPerPixel);
                int outIndex = (y * outStride) + (x * outBytesPerPixel);

                byte hibyte = inBuffer[inIndex];
                byte lobyte = inBuffer[inIndex+1];

                outBuffer[outIndex] = lobyte;
                outBuffer[outIndex+1] = hibyte;
            }
        }

        return outBuffer;
    }

    private static byte[] Convert16BitGrayScaleToRgb24(byte[] inBuffer, int width, int height)
    {
        int inBytesPerPixel = 2;
        int outBytesPerPixel = 3;

        byte[] outBuffer = new byte[width * height * outBytesPerPixel];
        int inStride = width * inBytesPerPixel;
        int outStride = width * outBytesPerPixel;

        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                int inIndex = (y * inStride) + (x * inBytesPerPixel);
                int outIndex = (y * outStride) + (x * outBytesPerPixel);

                byte hibyte = inBuffer[inIndex];
                byte lobyte = inBuffer[inIndex + 1];

                byte r, g, b;

                UInt16 color = (UInt16)(hibyte << 8 | lobyte);

                Convert16bitGSToRGB(color, out r, out g, out b);

                outBuffer[outIndex] = r;
                outBuffer[outIndex + 1] = g;
                outBuffer[outIndex + 2] = b;
            }
        }

        return outBuffer;
    }

    private static Bitmap CreateBitmapFromBytes(byte[] pixelValues, int width, int height)
    {
        //Create an image that will hold the image data

        Bitmap bmp = new Bitmap(width, height, PixelFormat.Format16bppRgb565);

        //Get a reference to the images pixel data
        Rectangle dimension = new Rectangle(0, 0, bmp.Width, bmp.Height);
        BitmapData picData = bmp.LockBits(dimension, ImageLockMode.ReadWrite, bmp.PixelFormat);
        IntPtr pixelStartAddress = picData.Scan0;

        //Copy the pixel data into the bitmap structure
        Marshal.Copy(pixelValues, 0, pixelStartAddress, pixelValues.Length);

        bmp.UnlockBits(picData);
        return bmp;
    }

但转换的结果仍然不令人满意/不正确。这是我应该得到的图片:

正在转换这里链接的文件:

Example RAW16 picture file

这是使用 Convert16BitGrayScaleToRgb48 的结果:

这是使用 Convert16BitGrayScaleToRgb16 的结果:

这是使用 Convert16BitGrayScaleToRgb24 的结果:

很明显，颜色重映射是错误的，但我无法理解问题出在哪里。

此外，我还发现 picturebox 没有准确显示它存储的内容。顶部的第二张图片(Convert16BitGrayScaleToRgb48 结果)是图片框显示的内容，而下图是我将图片保存为 PNG 格式时获得的图片:

我认为 RAW16 灰度应该意味着 2 个字节包含 16 位灰度值或在 565 或 555 map 上编码的 RGB 灰度值。但这些假设似乎都不符合真实情况。

有人提示如何转换源文件中提供的值以获得与第一个一样的图片(使用 ImageJ 从同一来源获得)？

Answer 1

我使用 GIMP 找到了一个可能的提示。如果我通过此应用程序加载原始文件(更改 .data 中的扩展名和/或强制将其加载为 RAW)并将其设置为 160x120 16bpp BigEndian 我得到了几乎是黑框 (!)，但如果我更改级别压缩当前唯一小峰值周围的范围(大约 12,0 黑色 - 13,0 白色)，图像结果正确。更改字节顺序非常简单，可以稍微压缩动态范围，但我正在努力。

从这次经历中学到的第一个教训是“不要相信你的眼睛”:-)。

我努力的最终结果是这三种方法:

public static void GetMinMax(byte[] data, out UInt16 min, out UInt16 max, bool big_endian = true)
{
    if (big_endian)
        min = max = (UInt16)((data[0] << 8) | data[1]);
    else
        min = max = (UInt16)((data[1] << 8) | data[0]);

    for (int i = 0; i < (data.Length - 1); i += 2)
    {
        UInt16 _value;

        if (big_endian)
            _value = (UInt16)((data[i] << 8) | data[i + 1]);
        else
            _value = (UInt16)((data[i + 1] << 8) | data[i]);

        if (_value < min)
            min = _value;

        if (_value > max)
            max = _value;
    }
}

public static void CompressRange(byte MSB, byte LSB, UInt16 min, UInt16 max, out byte color, Polarity polarity)
{
    UInt16 _value = (UInt16)((MSB << 8) | LSB);

    _value -= min;

    switch (polarity)
    {
        case Polarity.BlackHot:
            _value = (UInt16)((_value * 255) / (max - min));
            _value = (UInt16)(255 - _value);
            break;

        default:
        case Polarity.WhiteHot:
            _value = (UInt16)((_value * 255) / (max - min));
            break;
    }

    color = (byte)(_value & 0xff);
}

public static byte[] Convert16BitGrayScaleToRgb24(byte[] inBuffer, int width, int height, UInt16 min, UInt16 max, bool big_endian = true, Polarity polarity = Polarity.WhiteHot)
{
    int inBytesPerPixel = 2;
    int outBytesPerPixel = 3;

    byte[] outBuffer = new byte[width * height * outBytesPerPixel];
    int inStride = width * inBytesPerPixel;
    int outStride = width * outBytesPerPixel;

    for (int y = 0; y < height; y++)
    {
        for (int x = 0; x < width; x++)
        {
            int inIndex = (y * inStride) + (x * inBytesPerPixel);
            int outIndex = (y * outStride) + (x * outBytesPerPixel);

            byte hibyte;
            byte lobyte;

            if (big_endian)
            {
                hibyte = inBuffer[inIndex];
                lobyte = inBuffer[inIndex + 1];
            }
            else
            {
                hibyte = inBuffer[inIndex + 1];
                lobyte = inBuffer[inIndex];
            }

            byte gray;

            CompressRange(hibyte, lobyte, min, max, out gray, polarity);

            outBuffer[outIndex] = gray;
            outBuffer[outIndex + 1] = gray;
            outBuffer[outIndex + 2] = gray;
        }
    }

    return outBuffer;
}

这些允许加载附加到原始问题的文件并将其显示在标准 WindowsForm PictureBox 上。使用 48bpp 格式会导致某些图形卡上的图像质量下降(至少我的是这样)。 顺便说一句，无论环境的历史如何，GetMinMax 都会计算当前帧的最小最大值。这意味着，如果您要使用此功能来显示图片序列(就像我一样)，FOV 中平均温度的强烈变化将使整个图像发生不同的曝光，从而导致一些损失图片的细节。在这种情况下，我建议计算当前帧的最小值-最大值，但不要在 Convert16BitGrayScaleToRgb24 中使用它，而是对两个值使用移动平均值。