C# 圖片位深度轉至8位灰度影象，8位灰度影象轉為1位灰度影象
#region 二值化
#region Otsu閾值法二值化模組
/// <summary>
/// Otsu閾值
/// </summary>
/// <param name="b">點陣圖流</param>
/// <returns></returns>
public Bitmap OtsuThreshold(Bitmap bitmap)
{
// 影象灰度化
// b = Gray(b);
int width = bitmap.Width;
int height = bitmap.Height;
byte threshold = 0;
int[] hist = new int[256];
int AllPixelNumber = 0, PixelNumberSmall = 0, PixelNumberBig = 0;
double MaxValue, AllSum = 0, SumSmall = 0, SumBig, ProbabilitySmall, ProbabilityBig, Probability;
BitmapData bmpData = bitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
unsafe
{
byte* p = (byte*)bmpData.Scan0;
int offset = bmpData.Stride - width * 4;
for (int j = 0; j < height; j++)
{
for (int i = 0; i < width; i++)
{
hist[p[0]]++;
p += 4;
}
p += offset;
}
bitmap.UnlockBits(bmpData);
}
//計算灰度為I的畫素出現的概率
for (int i = 0; i < 256; i++)
{
AllSum += i * hist[i]; // 質量矩
AllPixelNumber += hist[i]; // 質量
}
MaxValue = -1.0;
for (int i = 0; i < 256; i++)
{
PixelNumberSmall += hist[i];
PixelNumberBig = AllPixelNumber - PixelNumberSmall;
if (PixelNumberBig == 0)
{
break;
}
SumSmall += i * hist[i];
SumBig = AllSum - SumSmall;
ProbabilitySmall = SumSmall / PixelNumberSmall;
ProbabilityBig = SumBig / PixelNumberBig;
Probability = PixelNumberSmall * ProbabilitySmall * ProbabilitySmall + PixelNumberBig * ProbabilityBig * ProbabilityBig;
if (Probability > MaxValue)
{
MaxValue = Probability;
threshold = (byte)i;
}
}
this.Threshoding(bitmap, threshold);
bitmap = twoBit(bitmap);
return bitmap; ;
}
#endregion
#region 固定閾值法二值化模組
public Bitmap Threshoding(Bitmap b, byte threshold)
{
int width = b.Width;
int height = b.Height;
BitmapData data = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
unsafe
{
byte* p = (byte*)data.Scan0;
int offset = data.Stride - width * 4;
byte R, G, B, gray;
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
R = p[2];
G = p[1];
B = p[0];
gray = (byte)((R * 19595 + G * 38469 + B * 7472) >> 16);
if (gray >= threshold)
{
p[0] = p[1] = p[2] = 255;
}
else
{
p[0] = p[1] = p[2] = 0;
}
p += 4;
}
p += offset;
}
b.UnlockBits(data);
return b;
}
}
#endregion
#region 建立1點陣圖像
/// <summary>
/// 建立1點陣圖像
/// </summary>
/// <param name="srcBitmap"></param>
/// <returns></returns>
public Bitmap twoBit(Bitmap srcBitmap)
{
int midrgb = System.Drawing.Color.FromArgb(128, 128, 128).ToArgb();
int stride;//簡單公式((width/8)+3)&(~3)
stride = (srcBitmap.Width % 8) == 0 ? (srcBitmap.Width / 8) : (srcBitmap.Width / 8) + 1;
stride = (stride % 4) == 0 ? stride : ((stride / 4) + 1) * 4;
int k = srcBitmap.Height * stride;
byte[] buf = new byte[k];
int x = 0, ab = 0;
for (int j = 0; j < srcBitmap.Height; j++)
{
k = j * stride;//因影象寬度不同、有的可能有填充位元組需要跳越
x = 0;
ab = 0;
for (int i = 0; i < srcBitmap.Width; i++)
{
//從灰度變單色（下法如果直接從彩色變單色效果不太好，不過反相也可以在這裡控制）
if ((srcBitmap.GetPixel(i, j)).ToArgb() > midrgb)
{
ab = ab * 2 + 1;
}
else
{
ab = ab * 2;
}
x++;
if (x == 8)
{
buf[k++] = (byte)ab;//每位元組賦值一次，陣列buf中儲存的是十進位制。
ab = 0;
x = 0;
}
}
if (x > 0)
{
//迴圈實現：剩餘有效資料不滿1位元組的情況下須把它們移往位元組的高位部分
for (int t = x; t < 8; t++) ab = ab * 2;
buf[k++] = (byte)ab;
}
}
int width = srcBitmap.Width;
int height = srcBitmap.Height;
Bitmap dstBitmap = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format1bppIndexed);
BitmapData dt = dstBitmap.LockBits(new Rectangle(0, 0, dstBitmap.Width, dstBitmap.Height), ImageLockMode.ReadWrite, dstBitmap.PixelFormat);
Marshal.Copy(buf, 0, dt.Scan0, buf.Length);
dstBitmap.UnlockBits(dt);
return dstBitmap;
}
#endregion
#endregion
/// <summary>
/// 建立8位灰度影象
/// </summary>
/// <param name="width"></param>
/// <param name="height"></param>
/// <returns></returns>
public static Bitmap CreateGrayscaleImage(int width, int height)
{
// create new image
Bitmap bmp = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
// set palette to grayscale
SetGrayscalePalette(bmp);
// return new image
return bmp;
}
///<summary>
/// Set pallete of the image to grayscale
///</summary>
public static void SetGrayscalePalette(Bitmap srcImg)
{
// check pixel format
if (srcImg.PixelFormat != System.Drawing.Imaging.PixelFormat.Format8bppIndexed)
throw new ArgumentException();
// get palette
ColorPalette cp = srcImg.Palette;
// init palette
for (int i = 0; i < 256; i++)
{
cp.Entries[i] = System.Drawing.Color.FromArgb(i, i, i);
}
srcImg.Palette = cp;
}
//#region 轉為位深度為8的灰度影象
/// <summary>
/// 轉為灰度影象，位深度也改變
/// </summary>
/// <param name="srcBitmap"></param>
/// <returns></returns>
public static Bitmap RGB2Gray(Bitmap srcBitmap)
{
int wide = srcBitmap.Width;
int height = srcBitmap.Height;
Rectangle rect = new Rectangle(0, 0, wide, height);
//將Bitmap鎖定到系統記憶體中,獲得BitmapData
BitmapData srcBmData = srcBitmap.LockBits(rect, ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
//建立Bitmap
Bitmap dstBitmap = CreateGrayscaleImage(wide, height);//這個函式在後面有定義
BitmapData dstBmData = dstBitmap.LockBits(rect, ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
//點陣圖中第一個畫素資料的地址。它也可以看成是點陣圖中的第一個掃描行
System.IntPtr srcPtr = srcBmData.Scan0;
System.IntPtr dstPtr = dstBmData.Scan0;
//將Bitmap物件的資訊存放到byte陣列中
int src_bytes = srcBmData.Stride * height;
byte[] srcValues = new byte[src_bytes];
int dst_bytes = dstBmData.Stride * height;
byte[] dstValues = new byte[dst_bytes];
//複製GRB資訊到byte陣列
System.Runtime.InteropServices.Marshal.Copy(srcPtr, srcValues, 0, src_bytes);
System.Runtime.InteropServices.Marshal.Copy(dstPtr, dstValues, 0, dst_bytes);
//根據Y=0.299*R+0.114*G+0.587B,Y為亮度
for (int i = 0; i < height; i++)
for (int j = 0; j < wide; j++)
{
//只處理每行中影象畫素資料,捨棄未用空間
//注意點陣圖結構中RGB按BGR的順序儲存
int k = 3 * j;
byte temp = (byte)(srcValues[i * srcBmData.Stride + k + 2] * .299 + srcValues[i * srcBmData.Stride + k + 1] * .587 + srcValues[i * srcBmData.Stride + k] * .114);
dstValues[i * dstBmData.Stride + j] = temp;
}
System.Runtime.InteropServices.Marshal.Copy(dstValues, 0, dstPtr, dst_bytes);
//解鎖點陣圖
srcBitmap.UnlockBits(srcBmData);
dstBitmap.UnlockBits(dstBmData);
return dstBitmap;
}