public class Deskew { // Representation of a line in the image. private class HougLine { // Count of points in the line. public int Count; // Index in Matrix. public int Index; // The line is represented as all x,y that solve y*cos(alpha)-x*sin(alpha)=d public double Alpha; }
// The Bitmap
public Bitmap _internalBmp;
// The range of angles to search for lines
const double ALPHA_START = -20;
const double ALPHA_STEP = 0.2;
const int STEPS = 40 * 5;
const double STEP = 1;
// Precalculation of sin and cos.
double[] _sinA;
double[] _cosA;
// Range of d
double _min;
int _count;
// Count of points that fit in a line.
int[] _hMatrix;
// Calculate the skew angle of the image cBmp.
public double GetSkewAngle()
{
// Hough Transformation
Calc();
// Top 20 of the detected lines in the image.
HougLine[] hl = GetTop(20);
// Average angle of the lines
double sum = 0;
int count = 0;
for (int i = 0; i <= 19; i++)
{
sum += hl[i].Alpha;
count += 1;
}
return sum / count;
}
// Calculate the Count lines in the image with most points.
private HougLine[] GetTop(int count)
{
HougLine[] hl = new HougLine[count];
for (int i = 0; i <= count - 1; i++)
{
hl[i] = new HougLine();
}
for (int i = 0; i <= _hMatrix.Length - 1; i++)
{
if (_hMatrix[i] > hl[count - 1].Count)
{
hl[count - 1].Count = _hMatrix[i];
hl[count - 1].Index = i;
int j = count - 1;
while (j > 0 && hl[j].Count > hl[j - 1].Count)
{
HougLine tmp = hl[j];
hl[j] = hl[j - 1];
hl[j - 1] = tmp;
j -= 1;
}
}
}
for (int i = 0; i <= count - 1; i++)
{
int dIndex = hl[i].Index / STEPS;
int alphaIndex = hl[i].Index - dIndex * STEPS;
hl[i].Alpha = GetAlpha(alphaIndex);
//hl[i].D = dIndex + _min;
}
return hl;
}
// Hough Transforamtion:
private void Calc()
{
int hMin = _internalBmp.Height / 4;
int hMax = _internalBmp.Height * 3 / 4;
Init();
for (int y = hMin; y <= hMax; y++)
{
for (int x = 1; x <= _internalBmp.Width - 2; x++)
{
// Only lower edges are considered.
if (IsBlack(x, y))
{
if (!IsBlack(x, y + 1))
{
Calc(x, y);
}
}
}
}
}
// Calculate all lines through the point (x,y).
private void Calc(int x, int y)
{
int alpha;
for (alpha = 0; alpha <= STEPS - 1; alpha++)
{
double d = y * _cosA[alpha] - x * _sinA[alpha];
int calculatedIndex = (int)CalcDIndex(d);
int index = calculatedIndex * STEPS + alpha;
try
{
_hMatrix[index] += 1;
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.ToString());
}
}
}
private double CalcDIndex(double d)
{
return Convert.ToInt32(d - _min);
}
private bool IsBlack(int x, int y)
{
Color c = _internalBmp.GetPixel(x, y);
double luminance = (c.R * 0.299) + (c.G * 0.587) + (c.B * 0.114);
return luminance < 140;
}
private void Init()
{
// Precalculation of sin and cos.
_cosA = new double[STEPS];
_sinA = new double[STEPS];
for (int i = 0; i < STEPS; i++)
{
double angle = GetAlpha(i) * Math.PI / 180.0;
_sinA[i] = Math.Sin(angle);
_cosA[i] = Math.Cos(angle);
}
// Range of d:
_min = -_internalBmp.Width;
_count = (int)(2 * (_internalBmp.Width + _internalBmp.Height) / STEP);
_hMatrix = new int[_count * STEPS];
}
private static double GetAlpha(int index)
{
return ALPHA_START + index * ALPHA_STEP;
}
}
自己写的调用方法
public static void DeskewImage(string fileName, byte binarizeThreshold) { //打开图像 Bitmap bmp = OpenImage(fileName);
Deskew deskew = new Deskew();
Bitmap tempBmp = CropImage(bmp, bmp.Width / 4, bmp.Height / 4, bmp.Width / 2, bmp.Height / 2);
deskew._internalBmp = BinarizeImage(tempBmp, binarizeThreshold);
double angle = deskew.GetSkewAngle();
bmp = RotateImage(bmp, (float)(-angle));
//保存图像(需要再还原图片原本的位深度)
SaveImage(bmp, fileName);
}
/// <summary>
/// 图像剪切
/// </summary>
/// <param name="bmp"></param>
/// <param name="StartX"></param>
/// <param name="StartY"></param>
/// <param name="w"></param>
/// <param name="h"></param>
/// <returns></returns>
private static Bitmap CropImage(Bitmap bmp, int StartX, int StartY, int w, int h)
{
try
{
Bitmap bmpOut = new Bitmap(w, h, PixelFormat.Format32bppArgb);
Graphics g = Graphics.FromImage(bmpOut);
g.DrawImage(bmp, new Rectangle(0, 0, w, h), new Rectangle(StartX, StartY, w, h), GraphicsUnit.Pixel);
g.Dispose();
return bmpOut;
}
catch
{
return null;
}
}
/// <summary>
/// 图像二值化
/// </summary>
/// <param name="b"></param>
/// <param name="threshold">阈值</param>
private static Bitmap BinarizeImage(Bitmap b, byte threshold)
{
int width = b.Width;
int height = b.Height;
BitmapData data = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format32bppRgb);
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;
}
}
/// <summary>
/// 图像旋转
/// </summary>
/// <param name="bmp"></param>
/// <param name="angle">角度</param>
/// <returns></returns>
private static Bitmap RotateImage(Bitmap bmp, float angle)
{
PixelFormat pixelFormat = bmp.PixelFormat;
PixelFormat pixelFormatOld = pixelFormat;
if (bmp.Palette.Entries.Count() > 0)
{
pixelFormat = PixelFormat.Format24bppRgb;
}
Bitmap tmpBitmap = new Bitmap(bmp.Width, bmp.Height, pixelFormat);
tmpBitmap.SetResolution(bmp.HorizontalResolution, bmp.VerticalResolution);
Graphics g = Graphics.FromImage(tmpBitmap);
try
{
g.FillRectangle(Brushes.White, 0, 0, bmp.Width, bmp.Height);
g.RotateTransform(angle);
g.DrawImage(bmp, 0, 0);
}
catch
{
}
finally
{
g.Dispose();
}
if (pixelFormatOld == PixelFormat.Format8bppIndexed) tmpBitmap = CopyTo8bpp(tmpBitmap);
else if (pixelFormatOld == PixelFormat.Format1bppIndexed) tmpBitmap = CopyTo1bpp(tmpBitmap);
return tmpBitmap;
}
在最后进行图片选择时，位深度为1、4、8的索引图片是没办法直接用Graphics进行旋转操作的，需要图像的PixelFormat再做旋转。
现在只实现位深度为1和8的索引图片还原。
private static Bitmap CopyTo1bpp(Bitmap b) { int w = b.Width, h = b.Height; Rectangle r = new Rectangle(0, 0, w, h); if (b.PixelFormat != PixelFormat.Format32bppPArgb) { Bitmap temp = new Bitmap(w, h, PixelFormat.Format32bppPArgb); temp.SetResolution(b.HorizontalResolution, b.VerticalResolution); Graphics g = Graphics.FromImage(temp); g.DrawImage(b, r, 0, 0, w, h, GraphicsUnit.Pixel); g.Dispose(); b = temp; } BitmapData bdat = b.LockBits(r, ImageLockMode.ReadOnly, b.PixelFormat); Bitmap b0 = new Bitmap(w, h, PixelFormat.Format1bppIndexed); b0.SetResolution(b.HorizontalResolution, b.VerticalResolution); BitmapData b0dat = b0.LockBits(r, ImageLockMode.ReadWrite, PixelFormat.Format1bppIndexed); for (int y = 0; y < h; y++) { for (int x = 0; x < w; x++) { int index = y * bdat.Stride + (x * 4); if (Color.FromArgb(Marshal.ReadByte(bdat.Scan0, index + 2), Marshal.ReadByte(bdat.Scan0, index + 1), Marshal.ReadByte(bdat.Scan0, index)).GetBrightness() > 0.5f) { int index0 = y * b0dat.Stride + (x >> 3); byte p = Marshal.ReadByte(b0dat.Scan0, index0); byte mask = (byte)(0x80 >> (x & 0x7)); Marshal.WriteByte(b0dat.Scan0, index0, (byte)(p | mask)); } } } b0.UnlockBits(b0dat); b.UnlockBits(bdat); return b0; }
private static Bitmap CopyTo8bpp(Bitmap bmp)
{
if (bmp == null) return null;
Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
BitmapData bmpData = bmp.LockBits(rect, ImageLockMode.ReadOnly, bmp.PixelFormat);
int width = bmpData.Width;
int height = bmpData.Height;
int stride = bmpData.Stride;
int offset = stride - width * 3;
IntPtr ptr = bmpData.Scan0;
int scanBytes = stride * height;
int posScan = 0, posDst = 0;
byte[] rgbValues = new byte[scanBytes];
Marshal.Copy(ptr, rgbValues, 0, scanBytes);
byte[] grayValues = new byte[width * height];
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
double temp = rgbValues[posScan++] * 0.11 +
rgbValues[posScan++] * 0.59 +
rgbValues[posScan++] * 0.3;
grayValues[posDst++] = (byte)temp;
}
posScan += offset;
}
Marshal.Copy(rgbValues, 0, ptr, scanBytes);
bmp.UnlockBits(bmpData);
Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
bitmap.SetResolution(bmp.HorizontalResolution, bmp.VerticalResolution);
BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
int offset0 = bitmapData.Stride - bitmapData.Width;
int scanBytes0 = bitmapData.Stride * bitmapData.Height;
byte[] rawValues = new byte[scanBytes0];
int posSrc = 0;
posScan = 0;
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
rawValues[posScan++] = grayValues[posSrc++];
}
posScan += offset0;
}
Marshal.Copy(rawValues, 0, bitmapData.Scan0, scanBytes0);
bitmap.UnlockBits(bitmapData);
ColorPalette palette;
using (Bitmap bmp0 = new Bitmap(1, 1, PixelFormat.Format8bppIndexed))
{
palette = bmp0.Palette;
}
for (int i = 0; i < 256; i++)
{
palette.Entries[i] = Color.FromArgb(i, i, i);
}
bitmap.Palette = palette;
return bitmap;
}
| 
转播
