I found this code on CodeProject site:
http://www.codeproject.com/KB/graphics/Deskew_an_Image.aspx
By mackenb | 25 Apr 2006
The article describes an algorithm to calculate the skew angle of an image.
This is converted to C#: (tested and working)
The Code:
enjoy...
http://www.codeproject.com/KB/graphics/Deskew_an_Image.aspx
By mackenb | 25 Apr 2006
The article describes an algorithm to calculate the skew angle of an image.
This is converted to C#: (tested and working)
The Code:
using System.Drawing;
using System.Drawing.Imaging;
using System;
using System.Diagnostics;
public class gmseDeskew
{
// Representation of a line in the image.
public 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;
public double d;
}
// The Bitmap
Bitmap cBmp;
// The range of angles to search for lines
double cAlphaStart = -20;
double cAlphaStep = 0.2;
int cSteps = 40 * 5;
// Precalculation of sin and cos.
double[] cSinA;
double[] cCosA;
// Range of d
double cDMin;
double cDStep = 1;
int cDCount;
// Count of points that fit in a line.
int[] cHMatrix;
// calculate the skew angle of the image cBmp
public double GetSkewAngle()
{
HougLine[] hl;
int i;
double sum = 0;
int count = 0;
//' Hough Transformation
Calc();
//' Top 20 of the detected lines in the image.
hl = GetTop(20);
//' Average angle of the lines
for (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;
int j;
HougLine tmp;
int AlphaIndex, dIndex;
hl = new HougLine[Count];
for (int i = 0; i < Count; i++)
{
hl[i] = new HougLine();
}
for (int i = 0; i < cHMatrix.Length - 1; i++)
{
if (cHMatrix[i] > hl[Count - 1].Count)
{
hl[Count - 1].Count = cHMatrix[i];
hl[Count - 1].Index = i;
j = Count - 1;
while (j > 0 && hl[j].Count > hl[j - 1].Count)
{
tmp = hl[j];
hl[j] = hl[j - 1];
hl[j - 1] = tmp;
j -= 1;
}
}
}
for (int i = 0; i < Count; i++)
{
dIndex = hl[i].Index / cSteps;
AlphaIndex = hl[i].Index - dIndex * cSteps;
hl[i].Alpha = GetAlpha(AlphaIndex);
hl[i].d = dIndex + cDMin;
}
return hl;
}
public void New(Bitmap bmp)
{
cBmp = bmp;
}
// ' Hough Transforamtion:
private void Calc()
{
int x;
int y;
int hMin = cBmp.Height / 4;
int hMax = cBmp.Height * 3 / 4;
Init();
for (y = hMin; y < hMax; y++)
{
for (x = 1; x < cBmp.Width - 2; x++)
{
//' Only lower edges are considered.
if (IsBlack(x, y) == true)
{
if (IsBlack(x, y + 1) == false)
{
Calc(x, y);
}
}
}
}
}
// ' Calculate all lines through the point (x,y).
private void Calc(int x, int y)
{
double d;
int dIndex;
int Index;
for (int alpha = 0; alpha < cSteps - 1; alpha++)
{
d = y * cCosA[alpha] - x * cSinA[alpha];
dIndex = (int)CalcDIndex(d);
Index = dIndex * cSteps + alpha;
try
{
cHMatrix[Index] += 1;
}
catch (Exception ex)
{
Debug.WriteLine(ex.ToString());
}
}
}
private double CalcDIndex(double d)
{
return Convert.ToInt32(d - cDMin);
}
private bool IsBlack(int x, int y)
{
Color c;
double luminance;
c = cBmp.GetPixel(x, y);
luminance = (c.R * 0.299) + (c.G * 0.587) + (c.B * 0.114);
return luminance < 140;
}
private void Init()
{
double angle;
//' Precalculation of sin and cos.
cSinA = new double[cSteps - 1];
cCosA = new double[cSteps - 1];
for (int i = 0; i < cSteps - 1; i++)
{
angle = GetAlpha(i) * Math.PI / 180.0;
cSinA[i] = Math.Sin(angle);
cCosA[i] = Math.Cos(angle);
}
//' Range of d
: cDMin = -cBmp.Width;
cDCount = (int)(2 * (cBmp.Width + cBmp.Height) / cDStep);
cHMatrix = new int[cDCount * cSteps];
}
public double GetAlpha(int Index)
{
return cAlphaStart + Index * cAlphaStep;
} public static Bitmap RotateImage(Bitmap bmp, double angle)
{
Graphics g;
Bitmap tmp = new Bitmap(bmp.Width, bmp.Height, PixelFormat.Format32bppRgb);
tmp.SetResolution(bmp.HorizontalResolution, bmp.VerticalResolution);
g = Graphics.FromImage(tmp);
try
{
g.FillRectangle(Brushes.White, 0, 0, bmp.Width, bmp.Height);
g.RotateTransform((float)angle);
g.DrawImage(bmp, 0, 0);
}
finally
{
g.Dispose();
}
return tmp;
}
}
using System.Drawing.Imaging;
using System;
using System.Diagnostics;
public class gmseDeskew
{
// Representation of a line in the image.
public 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;
public double d;
}
// The Bitmap
Bitmap cBmp;
// The range of angles to search for lines
double cAlphaStart = -20;
double cAlphaStep = 0.2;
int cSteps = 40 * 5;
// Precalculation of sin and cos.
double[] cSinA;
double[] cCosA;
// Range of d
double cDMin;
double cDStep = 1;
int cDCount;
// Count of points that fit in a line.
int[] cHMatrix;
// calculate the skew angle of the image cBmp
public double GetSkewAngle()
{
HougLine[] hl;
int i;
double sum = 0;
int count = 0;
//' Hough Transformation
Calc();
//' Top 20 of the detected lines in the image.
hl = GetTop(20);
//' Average angle of the lines
for (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;
int j;
HougLine tmp;
int AlphaIndex, dIndex;
hl = new HougLine[Count];
for (int i = 0; i < Count; i++)
{
hl[i] = new HougLine();
}
for (int i = 0; i < cHMatrix.Length - 1; i++)
{
if (cHMatrix[i] > hl[Count - 1].Count)
{
hl[Count - 1].Count = cHMatrix[i];
hl[Count - 1].Index = i;
j = Count - 1;
while (j > 0 && hl[j].Count > hl[j - 1].Count)
{
tmp = hl[j];
hl[j] = hl[j - 1];
hl[j - 1] = tmp;
j -= 1;
}
}
}
for (int i = 0; i < Count; i++)
{
dIndex = hl[i].Index / cSteps;
AlphaIndex = hl[i].Index - dIndex * cSteps;
hl[i].Alpha = GetAlpha(AlphaIndex);
hl[i].d = dIndex + cDMin;
}
return hl;
}
public void New(Bitmap bmp)
{
cBmp = bmp;
}
// ' Hough Transforamtion:
private void Calc()
{
int x;
int y;
int hMin = cBmp.Height / 4;
int hMax = cBmp.Height * 3 / 4;
Init();
for (y = hMin; y < hMax; y++)
{
for (x = 1; x < cBmp.Width - 2; x++)
{
//' Only lower edges are considered.
if (IsBlack(x, y) == true)
{
if (IsBlack(x, y + 1) == false)
{
Calc(x, y);
}
}
}
}
}
// ' Calculate all lines through the point (x,y).
private void Calc(int x, int y)
{
double d;
int dIndex;
int Index;
for (int alpha = 0; alpha < cSteps - 1; alpha++)
{
d = y * cCosA[alpha] - x * cSinA[alpha];
dIndex = (int)CalcDIndex(d);
Index = dIndex * cSteps + alpha;
try
{
cHMatrix[Index] += 1;
}
catch (Exception ex)
{
Debug.WriteLine(ex.ToString());
}
}
}
private double CalcDIndex(double d)
{
return Convert.ToInt32(d - cDMin);
}
private bool IsBlack(int x, int y)
{
Color c;
double luminance;
c = cBmp.GetPixel(x, y);
luminance = (c.R * 0.299) + (c.G * 0.587) + (c.B * 0.114);
return luminance < 140;
}
private void Init()
{
double angle;
//' Precalculation of sin and cos.
cSinA = new double[cSteps - 1];
cCosA = new double[cSteps - 1];
for (int i = 0; i < cSteps - 1; i++)
{
angle = GetAlpha(i) * Math.PI / 180.0;
cSinA[i] = Math.Sin(angle);
cCosA[i] = Math.Cos(angle);
}
//' Range of d
: cDMin = -cBmp.Width;
cDCount = (int)(2 * (cBmp.Width + cBmp.Height) / cDStep);
cHMatrix = new int[cDCount * cSteps];
}
public double GetAlpha(int Index)
{
return cAlphaStart + Index * cAlphaStep;
} public static Bitmap RotateImage(Bitmap bmp, double angle)
{
Graphics g;
Bitmap tmp = new Bitmap(bmp.Width, bmp.Height, PixelFormat.Format32bppRgb);
tmp.SetResolution(bmp.HorizontalResolution, bmp.VerticalResolution);
g = Graphics.FromImage(tmp);
try
{
g.FillRectangle(Brushes.White, 0, 0, bmp.Width, bmp.Height);
g.RotateTransform((float)angle);
g.DrawImage(bmp, 0, 0);
}
finally
{
g.Dispose();
}
return tmp;
}
}
enjoy...
