Skew angle checker for scanned documents.
The class implements document's skew checking algorithm, which is based on
The range of angles to detect is controlled by MaxSkewToDetect property.
The filter accepts 8 bpp grayscale images for processing.
Sample usage:
// create instance of skew checker DocumentSkewChecker skewChecker = new DocumentSkewChecker( ); // get documents skew angle double angle = skewChecker.GetSkewAngle( documentImage ); // create rotation filter RotateBilinear rotationFilter = new RotateBilinear( -angle ); rotationFilter.FillColor = Color.White; // rotate image applying the filter Bitmap rotatedImage = rotationFilter.Apply( documentImage ); Initial image:
Deskewed image:
protected void surfRansacBlendStraight(List <Bitmap> imgs)
{
MatrixH homography;
List <SpeededUpRobustFeaturePoint[]> surfPoints = new List <SpeededUpRobustFeaturePoint[]>();
//Calculate all the Surf Points
SpeededUpRobustFeaturesDetector surf = new SpeededUpRobustFeaturesDetector();
double lastAngle = 0;
for (int i = 0; i < imgs.Count; i++)
{
//Grayscale to find the edges and adjust the normal to point up
AForge.Imaging.Filters.GrayscaleBT709 grayscale = new AForge.Imaging.Filters.GrayscaleBT709();
AForge.Imaging.DocumentSkewChecker skew = new AForge.Imaging.DocumentSkewChecker();
double angle = skew.GetSkewAngle(grayscale.Apply(imgs[i]));
//Less than 5 deg change in angle to account for wobble, ignore big shifts
if (Math.Abs(angle - lastAngle) < 5)
{
AForge.Imaging.Filters.RotateBilinear rotate = new AForge.Imaging.Filters.RotateBilinear(angle);
rotate.FillColor = Color.FromArgb(0, 255, 255, 255);
imgs[i] = rotate.Apply(imgs[i]);
lastAngle = angle;
}
showImage(imgs[i]);
surfPoints.Add(surf.ProcessImage(imgs[i]).ToArray());
}
Bitmap final = imgs[0];
for (int i = 1; i < imgs.Count; i++)
{
SpeededUpRobustFeaturePoint[] surfFinal = surf.ProcessImage(final).ToArray();
//Correlate the Harris pts between imgs
KNearestNeighborMatching matcher = new KNearestNeighborMatching(5);
matcher.Threshold = 0.05;
IntPoint[][] matches = matcher.Match(surfFinal, surfPoints[i]);
//Create the homography matrix using RANSAC
RansacHomographyEstimator ransac = new RansacHomographyEstimator(0.015, 1);
homography = ransac.Estimate(matches[0], matches[1]);
Blend blend = new Blend(homography, final);
blend.Gradient = true;
final = blend.Apply(imgs[i]);
}
//Smooth/Sharpen if I wanted to
AForge.Imaging.Filters.Sharpen filter = new AForge.Imaging.Filters.Sharpen();
//AForge.Imaging.Filters.Gaussian filter = new AForge.Imaging.Filters.Guassian(5);
//filter.ApplyInPlace(final);
showImage(final);
}
public BitmapSource Apply(BitmapSource image)
{
var filter = new DocumentSkewChecker();
var bitmap = image.ToBitmap();
var grayscale = new Grayscale(0.2125, 0.7154, 0.0721).Apply(bitmap);
var angle = filter.GetSkewAngle(grayscale);
var rotationFilter = new RotateBilinear(-angle);
return rotationFilter.Apply(grayscale).ToBitmapImage();
}
protected void fastHarrisRansacBlendStraight(List <Bitmap> imgs)
{
List <IntPoint[]> harrisPoints = new List <IntPoint[]>();
MatrixH homography;
//Calculate all the Harris Points
HarrisCornersDetector harris = new HarrisCornersDetector(0.03f, 10000f);
for (int i = 0; i < imgs.Count; i++)
{
harrisPoints.Add(harris.ProcessImage(imgs[i]).ToArray());
}
Bitmap final = imgs[0];
for (int i = 1; i < imgs.Count; i++)
{
//Convert my frames to grayscale so I can find and adjust the normal vectors
AForge.Imaging.Filters.GrayscaleBT709 grayscale = new AForge.Imaging.Filters.GrayscaleBT709();
AForge.Imaging.DocumentSkewChecker skew = new AForge.Imaging.DocumentSkewChecker();
double finalAngle = skew.GetSkewAngle(grayscale.Apply(final));
double imgAngle = skew.GetSkewAngle(grayscale.Apply(imgs[i]));
//Less than 5% to account for human error with rotations and wobbles
if (Math.Abs(finalAngle - imgAngle) < 5)
{
AForge.Imaging.Filters.RotateBilinear rotate = new AForge.Imaging.Filters.RotateBilinear(finalAngle - imgAngle);
rotate.FillColor = Color.FromArgb(0, 255, 255, 255);
imgs[i] = rotate.Apply(imgs[i]);
//Update harris
harrisPoints[i] = harris.ProcessImage(imgs[i]).ToArray();
}
IntPoint[] harrisFinal = harris.ProcessImage(final).ToArray();
//Correlate the Harris pts between imgs
CorrelationMatching matcher = new CorrelationMatching(5, final, imgs[i]);
IntPoint[][] matches = matcher.Match(harrisFinal, harrisPoints[i]);
//Create the homography matrix using ransac
RansacHomographyEstimator ransac = new RansacHomographyEstimator(0.025, 0.99);
homography = ransac.Estimate(matches[0], matches[1]);
Blend blend = new Blend(homography, final);
blend.Gradient = true;
final = blend.Apply(imgs[i]);
}
showImage(final);
}
public IEnumerable<Bitmap> Apply(Bitmap bitmap)
{
// assuming scanned background is white we need to invert for the algo to work
var copy = new Invert().Apply(bitmap);
copy = EnsureGrayscale(copy);
new Threshold { ThresholdValue = 25 }.ApplyInPlace(copy);
new FillHoles().ApplyInPlace(copy);
var blobCounter = new BlobCounter
{
// set filtering options
FilterBlobs = true,
MinWidth = 50,
MinHeight = 50,
};
blobCounter.ProcessImage(copy);
var blobs = blobCounter.GetObjectsInformation();
if (blobs.Any())
{
var invertedOriginal = new Invert().Apply(bitmap);
foreach (var blob in blobs)
{
// use inverted source to ensure correct edge colors
blobCounter.ExtractBlobsImage(invertedOriginal, blob, false);
var blobImage = blob.Image.ToManagedImage();
// straighten
var angle = new DocumentSkewChecker().GetSkewAngle(EnsureGrayscale(blobImage));
var rotationFilter = new RotateBilinear(-angle) { FillColor = Color.Black };
blobImage = rotationFilter.Apply(blobImage);
// crop
blobImage = new ExtractBiggestBlob().Apply(blobImage);
new Invert().ApplyInPlace(blobImage);
yield return blobImage;
}
}
else
{
yield return bitmap;
}
}
private void RotateImage()
{
DocumentSkewChecker skewChecker = new DocumentSkewChecker();
skewChecker.MaxSkewToDetect = 45;
double angle = skewChecker.GetSkewAngle(_recogimg);
//Максимальный угол, при котором идет поворот - 45 градусов, после этого изображение не поворачивается
if (Math.Abs(angle) < 45)
{
RotateBilinear rotationFilter = new RotateBilinear(-angle, true);
rotationFilter.FillColor = Color.Black;
_recogimg = rotationFilter.Apply(_recogimg);
_markersimg = rotationFilter.Apply(_markersimg);
}
}
// 기울어짐 바로잡기
public static Bitmap skew(Bitmap source)
{
// create grayscale filter (BT709)
Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721); // 8비트 grayscale 로 바꾸고
// apply the filter
Bitmap grayImage = filter.Apply(source);
// create instance of skew checker
DocumentSkewChecker skewChecker = new DocumentSkewChecker(); // 8비트 grayscale 로 넣어줘야 함
// // get documents skew angle
double angle = skewChecker.GetSkewAngle(grayImage); // 기울어진 각도를 얻고
Bitmap tmp = source;
// convert to 24 bits per pixel
source = ImageProcess.Clone(tmp, PixelFormat.Format24bppRgb); // 로테이션 전에 24비트로 바꿔주고
// delete old image
tmp.Dispose();
// create rotation filter
RotateBilinear rotationFilter = new RotateBilinear(-angle);
rotationFilter.FillColor = Color.White;
// rotate image applying the filter
Bitmap rotatedImage = rotationFilter.Apply(source); // 원래 이미지를 가져다가 각도만큼 돌리고(원래 이미지는 24비트로 넣어줘야함)
return rotatedImage;
}
public static System.Drawing.Image AforgeAutoCrop(Bitmap selectedImage,
DetectBorderParam param)
{
// 一些参数的默认值
if (param.MinObjectWidth == 0)
param.MinObjectWidth = 500;
if (param.MinObjectHeight == 0)
param.MinObjectHeight = 500;
Bitmap autoCropImage = null;
try
{
autoCropImage = selectedImage;
// create grayscale filter (BT709)
Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721);
Bitmap grayImage = filter.Apply(autoCropImage);
// create instance of skew checker
DocumentSkewChecker skewChecker = new DocumentSkewChecker();
// get documents skew angle
double angle = skewChecker.GetSkewAngle(grayImage);
// create rotation filter
RotateBilinear rotationFilter = new RotateBilinear(-angle);
rotationFilter.FillColor = Color.White;
// rotate image applying the filter
Bitmap rotatedImage = rotationFilter.Apply(grayImage);
new ContrastStretch().ApplyInPlace(rotatedImage);
new Threshold(100).ApplyInPlace(rotatedImage);
BlobCounter bc = new BlobCounter();
bc.FilterBlobs = true;
bc.MinWidth = param.MinObjectWidth; // 500;
bc.MinHeight = param.MinObjectHeight; // 500;
bc.ProcessImage(rotatedImage);
Rectangle[] rects = bc.GetObjectsRectangles();
if (rects.Length == 0)
{
System.Windows.Forms.MessageBox.Show("No rectangle found in image ");
}
else if (rects.Length == 1)
{
autoCropImage = rotatedImage.Clone(rects[0], rotatedImage.PixelFormat);
}
else if (rects.Length > 1)
{
// get largets rect
Console.WriteLine("Using largest rectangle found in image ");
var r2 = rects.OrderByDescending(r => r.Height * r.Width).ToList();
autoCropImage = rotatedImage.Clone(r2[1], rotatedImage.PixelFormat);
}
else
{
Console.WriteLine("Huh? on image ");
}
}
catch (Exception ex)
{
// MessageBox.Show(ex.Message);
throw ex;
}
return autoCropImage;
}
public static bool GetSkewParam(Bitmap selectedImage,
DetectBorderParam param,
out double angle,
out Rectangle rect)
{
// 一些参数的默认值
if (param.MinObjectWidth == 0)
param.MinObjectWidth = 500;
if (param.MinObjectHeight == 0)
param.MinObjectHeight = 500;
Bitmap autoCropImage = null;
try
{
autoCropImage = selectedImage;
#if NO
// create grayscale filter (BT709)
Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721);
Bitmap grayImage = filter.Apply(autoCropImage);
#endif
Bitmap grayImage = selectedImage.Clone(new Rectangle(0, 0, selectedImage.Width, selectedImage.Height),
System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
// create instance of skew checker
DocumentSkewChecker skewChecker = new DocumentSkewChecker();
// get documents skew angle
angle = skewChecker.GetSkewAngle(grayImage);
// create rotation filter
RotateBilinear rotationFilter = new RotateBilinear(-angle);
rotationFilter.FillColor = Color.Black; // .White;
rotationFilter.KeepSize = true;
// rotate image applying the filter
Bitmap rotatedImage = rotationFilter.Apply(grayImage);
new ContrastStretch().ApplyInPlace(rotatedImage);
new Threshold(100).ApplyInPlace(rotatedImage);
BlobCounter bc = new BlobCounter();
bc.FilterBlobs = true;
bc.MinWidth = param.MinObjectWidth; // 500;
bc.MinHeight = param.MinObjectHeight; // 500;
#if NO
bc.MinWidth = 500;// grayImage.Width / 10; // 500
bc.MinHeight = 500;// grayImage.Height / 10; // 500
#endif
bc.ProcessImage(rotatedImage);
Rectangle[] rects = bc.GetObjectsRectangles();
if (rects.Length == 0)
{
// System.Windows.Forms.MessageBox.Show("No rectangle found in image ");
rect = new Rectangle(0, 0, 0, 0);
return false;
}
else if (rects.Length == 1)
{
rect = rects[0];
// autoCropImage = rotatedImage.Clone(rects[0], rotatedImage.PixelFormat);
}
else if (rects.Length > 1)
{
// TODO： 应该把这些矩形合并在一起
Rectangle first = new Rectangle(0, 0, 0, 0);
int i = 0;
foreach (Rectangle one in rects)
{
Debug.WriteLine("one=" + one.ToString());
if (i == 0)
first = one;
else
first = Merge(first, one);
i++;
}
rect = first;
Debug.WriteLine("result=" + rect.ToString());
#if NO
// get largets rect
Console.WriteLine("Using largest rectangle found in image ");
var r2 = rects.OrderByDescending(r => r.Height * r.Width).ToList();
rect = r2[1];
// autoCropImage = rotatedImage.Clone(r2[1], rotatedImage.PixelFormat);
#endif
}
else
{
// Console.WriteLine("Huh? on image ");
rect = new Rectangle(0, 0, 0, 0);
return false;
}
#if NO
Blob[] blobs = bc.GetObjectsInformation();
foreach (var blob in blobs)
{
List<IntPoint> edgePoints = blobCounter.GetBlobsEdgePoints(blob);
List<IntPoint> cornerPoints;
// use the shape checker to extract the corner points
if (shapeChecker.IsQuadrilateral(edgePoints, out cornerPoints))
{
// only do things if the corners form a rectangle
if (shapeChecker.CheckPolygonSubType(cornerPoints) == PolygonSubType.Rectangle)
{
// here i use the graphics class to draw an overlay, but you
// could also just use the cornerPoints list to calculate your
// x, y, width, height values.
List<Point> Points = new List<Point>();
foreach (var point in cornerPoints)
{
Points.Add(new Point(point.X, point.Y));
}
Graphics g = Graphics.FromImage(image);
g.DrawPolygon(new Pen(Color.Red, 5.0f), Points.ToArray());
image.Save("result.png");
}
}
}
#endif
}
catch (Exception ex)
{
// MessageBox.Show(ex.Message);
throw ex;
}
finally
{
if (autoCropImage != null)
autoCropImage.Dispose();
}
return true;
}
// 기울기 보정
private void button51_Click(object sender, EventArgs e)
{
///////////// ini 객체 생성 시작 /////////////////////////////////////////////////////
//현재 프로그램이 실행되고 있는정보 가져오기: 디버깅 모드라면 bin/debug/프로그램명.exe
FileInfo exefileinfo = new FileInfo(@"C:\Program Files\PLOCR\PLOCR.exe");
string pathini = exefileinfo.Directory.FullName.ToString(); //프로그램 실행되고 있는데 path 가져오기
string fileName = @"\PLOCRconfig.ini"; // 환경설정 파일명
string filePath = pathini + fileName; //ini 파일 경로
DocumentAnalysis.IniUtil ini = new DocumentAnalysis.IniUtil(filePath); // 만들어 놓았던 iniUtil 객체 생성(생성자 인자로 파일경로 정보 넘겨줌)
//////////// ini 객체 생성 끝 /////////////////////////////////////////////////////////
Bitmap source = Global.source;
// create grayscale filter (BT709)
Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721); // 8비트 grayscale 로 바꾸고
// apply the filter
Bitmap grayImage = filter.Apply(source);
grayImage.Save(@"C:\\Program Files\\PLOCR\\그레이스케일.png");
// create instance of skew checker
DocumentSkewChecker skewChecker = new DocumentSkewChecker(); // 8비트 grayscale 로 넣어줘야 함
// // get documents skew angle
double angle = skewChecker.GetSkewAngle(grayImage); // 기울어진 각도를 얻고
Bitmap tmp = source;
// convert to 24 bits per pixel
source = imageProcess.Clone(tmp, PixelFormat.Format24bppRgb); // 로테이션 전에 24비트로 바꿔주고
// delete old image
tmp.Dispose();
// create rotation filter
RotateBilinear rotationFilter = new RotateBilinear(-angle);
rotationFilter.FillColor = Color.White;
// rotate image applying the filter
Bitmap rotatedImage = rotationFilter.Apply(source); // 원래 이미지를 가져다가 각도만큼 돌리고(원래 이미지는 24비트로 넣어줘야함)
Global.source = rotatedImage;
pictureBox1.Image = Global.source;
pictureBox1.Invalidate();
ini.SetIniValue("기울어짐 바로잡기", "바로잡기 예/아니오", "예");
}
public static Bitmap Orient_Hough(Bitmap blob)
{
GC.Collect();
Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721);
Bitmap documentImage = filter.Apply(blob);
//Bitmap documentImage = AForge.Imaging.Image.Clone(blob, PixelFormat.Format16bppGrayScale); //force the jpgs
// create instance of skew checker
DocumentSkewChecker skewChecker = new DocumentSkewChecker();
// get documents skew angle
double angle = skewChecker.GetSkewAngle(documentImage);
// rotate image applying the filter
return RotateImg(blob, (int)-angle, Color.Transparent);
}
// Align scanned document
private void documentAligningMenuItem_Click( object sender, EventArgs e )
{
try
{
// get grayscale image from current image
Bitmap grayImage = ( image.PixelFormat == PixelFormat.Format8bppIndexed ) ?
AForge.Imaging.Image.Clone( image ) :
AForge.Imaging.Filters.Grayscale.CommonAlgorithms.BT709.Apply( image );
// threshold it using adaptive Otsu thresholding
OtsuThreshold threshold = new OtsuThreshold( );
threshold.ApplyInPlace( grayImage );
// get skew angle
DocumentSkewChecker skewChecker = new DocumentSkewChecker( );
double angle = skewChecker.GetSkewAngle( grayImage );
if ( ( angle < -skewChecker.MaxSkewToDetect ) ||
( angle > skewChecker.MaxSkewToDetect ) )
{
throw new ApplicationException( );
}
// create rotation filter
RotateBilinear rotationFilter = new RotateBilinear( -angle );
rotationFilter.FillColor = Color.White;
// rotate image applying the filter
ApplyFilter( rotationFilter );
}
catch
{
MessageBox.Show( "Failed determining skew angle. Is it reallly a scanned document?", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
}
}