///Improve the quality of the image.
///Process the image.
public async Task <string> GetTextFromImage(Bitmap image)
{
var ocr = new TesseractOCR();
var improvedImage = ImproveImageQuality(image);
var result = await ocr.GetText(improvedImage);
return(result);
}
private void FindLicensePlate(
VectorOfVectorOfPoint contours, int[,] hierachy, int idx, IInputArray gray, IInputArray canny,
List <IInputOutputArray> licensePlateImagesList, List <IInputOutputArray> filteredLicensePlateImagesList, List <RotatedRect> detectedLicensePlateRegionList,
List <String> licenses, int ocr_mode, int threshold_parameter)
{
for (; idx >= 0; idx = hierachy[idx, 0])
{
int numberOfChildren = GetNumberOfChildren(hierachy, idx);
//if it does not contains any children (charactor), it is not a license plate region
if (numberOfChildren == 0)
{
continue;
}
using (VectorOfPoint contour = contours[idx])
{
if (CvInvoke.ContourArea(contour) > 400)
{
if (numberOfChildren < 6)
{
//If the contour has less than 6 children, it is not a license plate (assuming license plate has at least 3 charactor)
//However we should search the children of this contour to see if any of them is a license plate
FindLicensePlate(contours, hierachy, hierachy[idx, 2], gray, canny, licensePlateImagesList,
filteredLicensePlateImagesList, detectedLicensePlateRegionList, licenses, ocr_mode, threshold_parameter);
continue;
}
RotatedRect box = CvInvoke.MinAreaRect(contour);
if (box.Angle < -45.0)
{
float tmp = box.Size.Width;
box.Size.Width = box.Size.Height;
box.Size.Height = tmp;
box.Angle += 90.0f;
}
else if (box.Angle > 45.0)
{
float tmp = box.Size.Width;
box.Size.Width = box.Size.Height;
box.Size.Height = tmp;
box.Angle -= 90.0f;
}
double whRatio = (double)box.Size.Width / box.Size.Height;
if (!(3.0 < whRatio && whRatio < 10.0))
//if (!(1.0 < whRatio && whRatio < 2.0))
{
//if the width height ratio is not in the specific range,it is not a license plate
//However we should search the children of this contour to see if any of them is a license plate
//Contour<Point> child = contours.VNext;
if (hierachy[idx, 2] > 0)
{
FindLicensePlate(contours, hierachy, hierachy[idx, 2], gray, canny, licensePlateImagesList,
filteredLicensePlateImagesList, detectedLicensePlateRegionList, licenses, ocr_mode, threshold_parameter);
}
continue;
}
using (UMat tmp1 = new UMat())
using (UMat tmp2 = new UMat())
{
PointF[] srcCorners = box.GetVertices();
PointF[] destCorners = new PointF[] {
new PointF(0, box.Size.Height - 1),
new PointF(0, 0),
new PointF(box.Size.Width - 1, 0),
new PointF(box.Size.Width - 1, box.Size.Height - 1)
};
using (Mat rot = CvInvoke.GetAffineTransform(srcCorners, destCorners))
{
//box.Center.X -= 20;
//box.Size.Height += 20;
//box.Size.Width += 20;
//box.Center.Y -= 20;
CvInvoke.WarpAffine(gray, tmp1, rot, Size.Round(box.Size));
}
SaveImageClass.SaveImage(gray, "gray2.jpg");
SaveImageClass.SaveImage(tmp1, "tmp1.jpg");
//resize the license plate such that the front is ~ 10-12. This size of front results in better accuracy from tesseract
Size approxSize = new Size(240, 180);
double scale = Math.Min(approxSize.Width / box.Size.Width, approxSize.Height / box.Size.Height);
Size newSize = new Size((int)Math.Round(box.Size.Width * scale), (int)Math.Round(box.Size.Height * scale));
CvInvoke.Resize(tmp1, tmp2, newSize, 0, 0, Inter.Cubic);
SaveImageClass.SaveImage(tmp1, "tmp1after.jpg");
SaveImageClass.SaveImage(tmp2, "tmp2.jpg");
//removes some pixels from the edge
int edgePixelSize = 3;
Rectangle newRoi = new Rectangle(new Point(edgePixelSize, edgePixelSize),
tmp2.Size - new Size(2 * edgePixelSize, 2 * edgePixelSize));
UMat plate = new UMat(tmp2, newRoi);
SaveImageClass.SaveImage(plate, "plate.jpg");
UMat filteredPlate = new UMat();
filteredPlate = FilterPlate(plate, threshold_parameter);
SaveImageClass.SaveImage(filteredPlate, "filtered.jpg");
StringBuilder strBuilder = new StringBuilder();
switch (ocr_mode)
{
case 1:
{
strBuilder = TesseractOCR.GetText(filteredPlate, _ocr);
break;
}
case 2:
{
strBuilder = GoogleApiOCR.GetText(filteredPlate);
break;
}
case 3:
{
strBuilder = ComputerVisionOCR.GetText(filteredPlate);
break;
}
default:
break;
}
if (strBuilder != null)
{
licenses.Add(strBuilder.ToString());
licensePlateImagesList.Add(plate);
filteredLicensePlateImagesList.Add(filteredPlate);
detectedLicensePlateRegionList.Add(box);
}
}
}
}
}
}