Develop Reference

Highlight winforms MS Chart line on hover

I'm trying to use MS Chart with custom controls. My purpose is to:
Highlight only a segment of the line that connects two neighboring points on mouse hover over that piece
Find indexes of those two neighboring points (I need that for being able to drag that line by moving two points simultaneously)
Kind of illustration:
For now I can detect a hover over a line on the chart by using the approach described here. But I'm stuck in finding indexes or at least coordinates of those two points.

So the original idea from this question was to find nearest points by x (assuming that all the series has x-values are indeed steadily increasing) and then calculate y-value. But I have a little improved that and added support for completely vertical lines. So here is my code for capturing the needed line:
private static GrippedLine? LineHitTest(Series series, double xPos, double yPos, Axis xAxis, Axis yAxis)
{
double xPixelPos = xAxis.PixelPositionToValue(xPos);
double yPixelPos = yAxis.PixelPositionToValue(yPos);
DataPoint[] neighbors = new DataPoint[2];
neighbors[0] = series.Points.Last(x => x.XValue <= xPixelPos);
neighbors[1] = series.Points.First(x => x.XValue >= xPixelPos);
DataPoint[] verticalMates;
foreach (DataPoint neighbor in neighbors)
{
if (Math.Abs(neighbor.XValue - xPixelPos) < LINE_GRIP_REGION)
{
verticalMates = series.Points.FindAllByValue(neighbor.XValue, "X").ToArray();
if (verticalMates.Length > 1)
{
if (verticalMates.Length > 2)
{
if (verticalMates[0].YValues[0] < verticalMates[verticalMates.Length - 1].YValues[0])
{
neighbors[0] = verticalMates.LastOrDefault(y => y.YValues[0] < yPixelPos);
neighbors[1] = verticalMates.FirstOrDefault(y => y.YValues[0] >= yPixelPos);
}
else
{
neighbors[0] = verticalMates.LastOrDefault(y => y.YValues[0] > yPixelPos);
neighbors[1] = verticalMates.FirstOrDefault(y => y.YValues[0] <= yPixelPos);
}
}
else
{
neighbors[0] = verticalMates[0];
neighbors[1] = verticalMates[1];
}
break;
}
}
}
double x0 = xAxis.ValueToPixelPosition(neighbors[0].XValue);
double y0 = yAxis.ValueToPixelPosition(neighbors[0].YValues[0]);
double x1 = xAxis.ValueToPixelPosition(neighbors[1].XValue);
double y1 = yAxis.ValueToPixelPosition(neighbors[1].YValues[0]);
double Yinterpolated = y0 + (y1 - y0) * (xPos - x0) / (x1 - x0);
int[] linePoints = new int[2];
// if mouse Y position is near the calculated OR the line is vertical
if (Math.Abs(Yinterpolated - yPos) < LINE_GRIP_REGION || neighbors[0].XValue == neighbors[1].XValue)
{
linePoints[0] = series.Points.IndexOf(neighbors[0]);
linePoints[1] = series.Points.IndexOf(neighbors[1]);
}
else
{
return null;
}
return new GrippedLine()
{
startLinePointIndex = linePoints[0],
endLinePointIndex = linePoints[1],
x0Correction = neighbors[0].XValue - xPixelPos,
y0Correction = neighbors[0].YValues[0] - yPixelPos,
x1Correction = neighbors[1].XValue - xPixelPos,
y1Correction = neighbors[1].YValues[0] - yPixelPos
};
}

Detect display corners with Emgu

I want to detect a display on an image (more precisely its corners).
I segment the image in display color and not display color:
Image<Gray, byte> segmentedImage = greyImage.InRange(new Gray(180), new Gray(255));
Then I use corner Harris to find the corners:
Emgu.CV.Image<Emgu.CV.Structure.Gray, Byte> harrisImage = new Image<Emgu.CV.Structure.Gray, Byte>(greyImage.Size);
CvInvoke.CornerHarris(segmentedImage, harrisImage, 2);
CvInvoke.Normalize(harrisImage, harrisImage, 0, 255, NormType.MinMax, DepthType.Cv32F);
There are now white pixels in the corners, but I cannot access them:
for (int j = 0; j < harrisImage.Rows; j++)
{
for (int i = 0; i < harrisImage.Cols; i++)
{
Console.WriteLine(harrisImage[j, i].Intensity);
}
}
It writes only 0s. How can I access them? And if I can access them, how can I find the 4 corners of the screen in the harris image? Is there a function to find a perspectively transformed rectangle from points?
EDIT:
On the OpenCV IRC they said FindContours is not that precise. And when I try to run it on the segmentedImage, I get this:
(ran FindContours on the segmentedImage, then ApproxPolyDP and drew the found contour on the original greyscale image)
I cannot get it to find the contours more precise...
EDIT2:
I cannot get this to work for me. Even with your code, I get the exact same result...
Here is my full Emgu code:
Emgu.CV.Image<Emgu.CV.Structure.Gray, Byte> imageFrameGrey = new Image<Emgu.CV.Structure.Gray, Byte>(bitmap);
Image<Gray, byte> segmentedImage = imageFrameGrey.InRange(new Gray(180), new Gray(255));
// get rid of small objects
int morph_size = 2;
Mat element = CvInvoke.GetStructuringElement(Emgu.CV.CvEnum.ElementShape.Rectangle, new System.Drawing.Size(2 * morph_size + 1, 2 * morph_size + 1), new System.Drawing.Point(morph_size, morph_size));
CvInvoke.MorphologyEx(segmentedImage, segmentedImage, Emgu.CV.CvEnum.MorphOp.Open, element, new System.Drawing.Point(-1, -1), 1, Emgu.CV.CvEnum.BorderType.Default, new MCvScalar());
// Find edges that form rectangles
List<RotatedRect> boxList = new List<RotatedRect>();
using (VectorOfVectorOfPoint contours = new VectorOfVectorOfPoint())
{
CvInvoke.FindContours(segmentedImage, contours, null, Emgu.CV.CvEnum.RetrType.External, ChainApproxMethod.ChainApproxSimple);
int count = contours.Size;
for (int i = 0; i < count; i++)
{
using (VectorOfPoint contour = contours[i])
using (VectorOfPoint approxContour = new VectorOfPoint())
{
CvInvoke.ApproxPolyDP(contour, approxContour, CvInvoke.ArcLength(contour, true) * 0.01, true);
if (CvInvoke.ContourArea(approxContour, false) > 10000)
{
if (approxContour.Size == 4)
{
bool isRectangle = true;
System.Drawing.Point[] pts = approxContour.ToArray();
LineSegment2D[] edges = Emgu.CV.PointCollection.PolyLine(pts, true);
for (int j = 0; j < edges.Length; j++)
{
double angle = Math.Abs(edges[(j + 1) % edges.Length].GetExteriorAngleDegree(edges[j]));
if (angle < 80 || angle > 100)
{
isRectangle = false;
break;
}
}
if (isRectangle)
boxList.Add(CvInvoke.MinAreaRect(approxContour));
}
}
}
}
}

So as promised i tried it myself. In C++ but you should adopt it easy to Emgu.
First i get rid of small object in your segmented image with an opening:
int morph_elem = CV_SHAPE_RECT;
int morph_size = 2;
Mat element = getStructuringElement(morph_elem, Size(2 * morph_size + 1, 2 * morph_size + 1), Point(morph_size, morph_size));
// Apply the opening
morphologyEx(segmentedImage, segmentedImage_open, CV_MOP_OPEN, element);
Then detect all the contours and take the large ones and check for rectangular shape:
vector< vector<Point>> contours;
findContours(segmentedImage_open, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
for each (vector<Point> var in contours)
{
double area = contourArea(var);
if (area> 30000)
{
vector<Point> approx;
approxPolyDP(var, approx, 0.01*arcLength(var, true), true);
if (4 == approx.size()) //rectangular shape
{
// do something
}
}
}
Here is the result with the contour in red and the approximated curve in green:
Edit:
You can improve your code by increasing the approximation factor until you get a contour with 4 points or you pass a threshold. Just wrap a for loop around approxPolyDP. You can define a range for your approximation value and prevent your code to fail if your object differs too much from a rectangle.

Finding Minimum Distance between Contours

I have many shapes in image which I want to save their contours in arrays .
I mean that I want the coordinates for contours for shape 1 in array 1 , for shape 2 in array 2 ext...
And if there are two shapes how can I draw the shortest line between them using their coordinates?
for example I had this result after many operations on an image
after finding contours :
So I need the coordinates for each shape contour to calculate the shortest distance between them

You can refer this link & this wiki for detecting Contours from an Image.
To find the min Distance from two Shapes follow the following steps:
Find the two Contours for which you want to find the min distance between them.
Cycle through each point in the Two contours & find the distance between them.
Take the minimum Distance by comparing all other distances & Mark that Points.
Here is the EMGUCV Implementation for this algorithm.
private void button2_Click(object sender, EventArgs e)
{
Image<Gray, byte> Img_Scene_Gray = Img_Source_Bgr.Convert<Gray, byte>();
Image<Bgr, byte> Img_Result_Bgr = Img_Source_Bgr.Copy();
LineSegment2D MinIntersectionLineSegment = new LineSegment2D();
Img_Scene_Gray = Img_Scene_Gray.ThresholdBinary(new Gray(10), new Gray(255));
#region Finding Contours
using (MemStorage Scene_ContourStorage = new MemStorage())
{
for (Contour<Point> Contours_Scene = Img_Scene_Gray.FindContours(CHAIN_APPROX_METHOD.CV_CHAIN_APPROX_SIMPLE,
RETR_TYPE.CV_RETR_EXTERNAL, Scene_ContourStorage); Contours_Scene != null; Contours_Scene = Contours_Scene.HNext)
{
if (Contours_Scene.Area > 25)
{
if (Contours_Scene.HNext != null)
{
MinIntersectionLine(Contours_Scene, Contours_Scene.HNext, ref MinIntersectionLineSegment);
Img_Result_Bgr.Draw(MinIntersectionLineSegment, new Bgr(Color.Green), 2);
}
Img_Result_Bgr.Draw(Contours_Scene, new Bgr(Color.Red), 1);
}
}
}
#endregion
imageBox1.Image = Img_Result_Bgr;
}
void MinIntersectionLine(Contour<Point> a, Contour<Point> b,ref LineSegment2D Line)
{
double MinDist = 10000000;
for (int i = 0; i < a.Total; i++)
{
for (int j = 0; j < b.Total; j++)
{
double Dist = Distance_BtwnPoints(a[i], b[j]);
if (Dist < MinDist)
{
Line.P1 = a[i];
Line.P2 = b[j];
MinDist = Dist;
}
}
}
}
double Distance_BtwnPoints(Point p, Point q)
{
int X_Diff = p.X - q.X;
int Y_Diff = p.Y - q.Y;
return Math.Sqrt((X_Diff * X_Diff) + (Y_Diff * Y_Diff));
}

How to use iterator in C# with EmguCV?

In OpenCV I use std::vector<std::vector<cv::Point>>::const_iterator like the code here:
std::vector<std::vector<cv::Point>> contours;
cv::findContours(contour,contours,CV_RETR_TREE,CV_CHAIN_APPROX_SIMPLE);
std::vector<std::vector<cv::Point>>::const_iterator itContours = contours.begin();
while(itContours != contours.end())
{
if(Condition1)
itContours = contours.erase(itContours);
else if(Condition2)
itContours = contours.erase(itContours);
else if(Condition3)
itContours = contours.erase(itContours);
else
++itContours;
}
But now I start using EmguCV but I can't find how to do like the code above. How can I do it?

Have a look at the shape detection example in the EMGU.Examples folder. It shows you how to deal with contours. I have copied the relevant code below for your reference but it's much better to have a look at the example.
#region Find triangles and rectangles
List<Triangle2DF> triangleList = new List<Triangle2DF>();
List<MCvBox2D> boxList = new List<MCvBox2D>(); //a box is a rotated rectangle
using (MemStorage storage = new MemStorage()) //allocate storage for contour approximation
for (Contour<Point> contours = cannyEdges.FindContours(Emgu.CV.CvEnum.CHAIN_APPROX_METHOD.CV_CHAIN_APPROX_SIMPLE, Emgu.CV.CvEnum.RETR_TYPE.CV_RETR_LIST, storage); contours != null; contours = contours.HNext)
{
Contour<Point> currentContour = contours.ApproxPoly(contours.Perimeter * 0.05, storage);
if (currentContour.Area > 250) //only consider contours with area greater than 250
{
if (currentContour.Total == 3) //The contour has 3 vertices, it is a triangle
{
Point[] pts = currentContour.ToArray();
triangleList.Add(new Triangle2DF(
pts[0],
pts[1],
pts[2]
));
}
else if (currentContour.Total == 4) //The contour has 4 vertices.
{
#region determine if all the angles in the contour are within [80, 100] degree
bool isRectangle = true;
Point[] pts = currentContour.ToArray();
LineSegment2D[] edges = PointCollection.PolyLine(pts, true);
for (int i = 0; i < edges.Length; i++)
{
double angle = Math.Abs(
edges[(i + 1) % edges.Length].GetExteriorAngleDegree(edges[i]));
if (angle < 80 || angle > 100)
{
isRectangle = false;
break;
}
}
#endregion
if (isRectangle) boxList.Add(currentContour.GetMinAreaRect());
}
}
}
#endregion
Let me know if you need any additional help and if any errors pop up,
Cheers,
Chris

XNA Draw a filled circle

In another thread on XNA, Callum Rogers wrote some code which creates a texture with the outline of a circle, but I'm trying to create a circle filled with a color. What I have to modify on this code to fill the circle with color?
public Texture2D CreateCircle(int radius)
{
int outerRadius = radius*2 + 2; // So circle doesn't go out of bounds
Texture2D texture = new Texture2D(GraphicsDevice, outerRadius, outerRadius);
Color[] data = new Color[outerRadius * outerRadius];
// Colour the entire texture transparent first.
for (int i = 0; i < data.Length; i++)
data[i] = Color.Transparent;
// Work out the minimum step necessary using trigonometry + sine approximation.
double angleStep = 1f/radius;
for (double angle = 0; angle < Math.PI*2; angle += angleStep)
{
// Use the parametric definition of a circle: http://en.wikipedia.org/wiki/Circle#Cartesian_coordinates
int x = (int)Math.Round(radius + radius * Math.Cos(angle));
int y = (int)Math.Round(radius + radius * Math.Sin(angle));
data[y * outerRadius + x + 1] = Color.White;
}
texture.SetData(data);
return texture;
}

Don't use a texture for stuff like this (especially for things being in one single color!) - also don't try to do it pixel by pixel. You've got 3D acceleration for a reason.
Just draw the circle similar to a pie using a triangle fan. You'll need the following vertices.
Center of the circle
x points on the circle's border.
The first two points will define a line between the center of the circle and its border. The third vertex will define the first polygon. Vertices 1, 3 and 4 will then define the second polygon, etc.
To get the points on the circle's border use the formulas from your example. The first angle will be 0°, the following ones multiples of (360° / points on circle). To get a full circle you'll need one additional point that matches the second point (the first point on the border).
Depending on the number of vertices on the circle you'll get different n-gons. The more vertices you use the rounder the shape will look (at some performance cost):
(Less than 2 vertices aren't possible as a polygon requires at least 3 vertices to be drawn.)
Total of 4 points (3 points on circle) will result in a triangle.
Total of 5 points (4 point on circle) will result in a square.
Total of 6 points (5 points on circle) will result in a pentagon
...
Actually the XNA example for drawing primites show how to draw a circle (or n-gon) using a triangle fan.

well for anyone who wants to do it pixel by pixel ... i made a solution based on the information given. In your 2d texture method add the following code to fill the circle. I'm making a game and wanted to be able to make circles different colors and sizes. So inside CreateCircle(int radius) method, add the following code after the outline has been created :
bool finished = false;
int firstSkip = 0;
int lastSkip = 0;
for (int i = 0; i <= data.Length - 1; i++)
{
if (finished == false)
{
//T = transparent W = White;
//Find the First Batch of Colors TTTTWWWTTTT The top of the circle
if ((data[i] == Color.White) && (firstSkip == 0))
{
while (data[i + 1] == Color.White)
{
i++;
}
firstSkip = 1;
i++;
}
//Now Start Filling TTTTTTTTWWTTTTTTTT
//circle in Between TTTTTTW--->WTTTTTT
//transaparent blancks TTTTTWW--->WWTTTTT
// TTTTTTW--->WTTTTTT
// TTTTTTTTWWTTTTTTTT
if (firstSkip == 1)
{
if (data[i] == Color.White && data[i + 1] != Color.White)
{
i++;
while (data[i] != Color.White)
{
//Loop to check if its the last row of pixels
//We need to check this because of the
//int outerRadius = radius * 2 + -->'2'<--;
for (int j = 1; j <= outerRadius; j++)
{
if (data[i + j] != Color.White)
{
lastSkip++;
}
}
//If its the last line of pixels, end drawing
if (lastSkip == outerRadius)
{
break;
finished = true;
}
else
{
data[i] = Color.White;
i++;
lastSkip = 0;
}
}
while (data[i] == Color.White)
{
i++;
}
i--;
}
}
}
}
// Set the data when finished
//-- don't need to paste this part, already given up above
texture.SetData(data);
return texture;

If you need to do it from scratch (though I'm guessing there are easier ways), change the way you perform the rendering. Instead of iterating through angles and plotting pixels, iterate through pixels and determine where they are relative to the circle. If they are <R, draw as fill color. If they are ~= R, draw as border color.

I know that I'm a little late, but I modified your code to fill in the center
public static Texture2D CreateCircle(GraphicsDevice importedGraphicsDevice, int radius)
{
int outerRadius = radius * 2 + 2; // So circle doesn't go out of bounds
Texture2D texture = new Texture2D(importedGraphicsDevice, outerRadius, outerRadius);
Color[] data = new Color[outerRadius * outerRadius];
// Colour the entire texture transparent first.
for (int i = 0; i < data.Length; i++)
data[i] = Color.Transparent;
// Work out the minimum step necessary using trigonometry + sine approximation.
double angleStep = 1f / radius;
for (double angle = 0; angle < Math.PI * 2; angle += angleStep)
{
// Use the parametric definition of a circle: http://en.wikipedia.org/wiki/Circle#Cartesian_coordinates
int x = (int)Math.Round(radius + radius * Math.Cos(angle));
int y = (int)Math.Round(radius + radius * Math.Sin(angle));
data[y * outerRadius + x + 1] = Color.White;
}
//width
for (int i = 0; i < outerRadius; i++)
{
int yStart = -1;
int yEnd = -1;
//loop through height to find start and end to fill
for (int j = 0; j < outerRadius; j++)
{
if (yStart == -1)
{
if (j == outerRadius - 1)
{
//last row so there is no row below to compare to
break;
}
//start is indicated by Color followed by Transparent
if (data[i + (j * outerRadius)] == Color.White && data[i + ((j + 1) * outerRadius)] == Color.Transparent)
{
yStart = j + 1;
continue;
}
}
else if (data[i + (j * outerRadius)] == Color.White)
{
yEnd = j;
break;
}
}
//if we found a valid start and end position
if (yStart != -1 && yEnd != -1)
{
//height
for (int j = yStart; j < yEnd; j++)
{
data[i + (j * outerRadius)] = new Color(10, 10, 10, 10);
}
}
}
texture.SetData(data);
return texture;
}