医学影像调窗技术

转自：/article/6019812.html

在年初的时候做过一个dicom格式文件解析，当时只是提了下。看着跟别人的显示出来也差不多 其实是我想太简单了。整理了下思路 这里提供正确的调窗代码。 医学影像 说得挺高科技的 其实在这个过程中本身没太复杂的图像处理技术。窗值处理就算是比较“高深”的了 也就是调窗。
网上都是啥基于 DCMTK的DICOM医学图像显示及其调窗方法研究 说得文绉绉的 没啥鸟用 ，dicom没你想象的那么复杂哈 咱这个全是自主代码 顶多看了点C++的源码 然后改成c#版本的 其实都一样的。

这中间有几个 步骤，
1 字节序转换
2 保留有效位，使用&进行位运算截取有效位
3 根据有无符号进行值转换
4 针对CT影像的窗值偏移处理
5 窗值映射 也就是映射到256级灰度（参考上一篇 ）

而我原来的代码啥都没做 直接对两个字节的数据进行toUint16 然后就进行窗值映射，还有就是也没有进行预设窗值读取。那么这样做的后果是什么呢 。
我们先加上预设窗值读取，首先我们加上几个变量 进行影像显示的几个关键数据 图像的长 宽 默认窗值 颜色采样数 1为灰度3为彩色 数据存储位数 有效位数 最高位数，具体查看dicom标准。
变量声明 默认窗值读取代码 （预设窗宽tag 0028 1051 预设窗位tag 0028 1050）：

public unsafe Bitmap convertTo8(BinaryReader streamdata, int colors, bool littleEdition, bool signed, short nHighBit,
int dataLen, float rescaleSlope, float rescaleIntercept, float windowCenter, float windowWidth, int width, int height)
{
Bitmap bmp = new Bitmap(width, height);
Graphics gg = Graphics.FromImage(bmp);
gg.Clear(Color.Green);
BitmapData bmpDatas = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),
System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
long numPixels = width * height;

if (colors == 3)//color Img
{
byte* p = (byte*)bmpDatas.Scan0;
int indx = 0;
for (int i = 0; i < bmp.Height; i++)
{
for (int j = 0; j < bmp.Width; j++)
{
p[indx + 2] = streamdata.ReadByte();
p[indx + 1] = streamdata.ReadByte();
p[indx] = streamdata.ReadByte();
indx += 3;
}
}
}
else if (colors == 1)//grayscale Img
{
byte* p = (byte*)bmpDatas.Scan0;
int nMin = ~(0xffff << (nHighBit + 1)), nMax = 0;
int indx = 0;//byteData index

for (int n = 0; n < numPixels; n++)//pixNum index
{
short nMask; nMask = (short)(0xffff << (nHighBit + 1));
short nSignBit;

byte[] pixData = null;
short pixValue = 0;

pixData = streamdata.ReadBytes(dataLen / 8 * colors);
if (nHighBit <= 15 && nHighBit > 7)
{
if (littleEdition == false)
Array.Reverse(pixData, 0, 2);

// 1. Clip the high bits.
if (signed == false)// Unsigned integer
{
pixValue = (short)((~nMask) & (BitConverter.ToInt16(pixData, 0)));
}
else
{
nSignBit = (short)(1 << nHighBit);
if (((BitConverter.ToInt16(pixData, 0)) & nSignBit) != 0)
pixValue = (short)(BitConverter.ToInt16(pixData, 0) | nMask);
else
pixValue = (short)((~nMask) & (BitConverter.ToInt16(pixData, 0)));
}
}
else if (nHighBit <= 7)
{
if (signed == false)// Unsigned integer
{
nMask = (short)(0xffff << (nHighBit + 1));
pixValue = (short)((~nMask) & (pixData[0]));
}
else
{
nMask = (short)(0xffff << (nHighBit + 1));
nSignBit = (short)(1 << nHighBit);
if (((pixData[0]) & nSignBit) != 0)
pixValue = (short)((short)pixData[0] | nMask);
else
pixValue = (short)((~nMask) & (pixData[0]));
}

}

// 2. Rescale if needed (especially for CT)
if ((rescaleSlope != 1.0f) || (rescaleIntercept != 0.0f))
{
float fValue = pixValue * rescaleSlope + rescaleIntercept;
pixValue = (short)fValue;
}

// 3. Window-level or rescale to 8-bit
if ((windowCenter != 0) || (windowWidth != 0))
{
float fSlope;
float fShift;
float fValue;

fShift = windowCenter - windowWidth / 2.0f;
fSlope = 255.0f / windowWidth;

fValue = ((pixValue) - fShift) * fSlope;
if (fValue < 0)
fValue = 0;
else if (fValue > 255)
fValue = 255;

p[indx++] = (byte)fValue;
p[indx++] = (byte)fValue;
p[indx++] = (byte)fValue;
}
else
{
// We will map the whole dynamic range.
float fSlope;
float fValue;

int i = 0;
// First compute the min and max.
if (n == 0)
nMin = nMax = pixValue;
else
{
if (pixValue < nMin)
nMin = pixValue;

if (pixValue > nMask)
nMask = pixValue;
}

// Calculate the scaling factor.
if (nMax != nMin)
fSlope = 255.0f / (nMax - nMin);
else
fSlope = 1.0f;

fValue = ((pixValue) - nMin) * fSlope;
if (fValue < 0)
fValue = 0;
else if (fValue > 255)
fValue = 255;

p[indx++] = (byte)fValue;
}
}
}

bmp.UnlockBits(bmpDatas);
//bmp.Dispose();
return bmp;
}

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