How to measure distance between two dark squares

[Requan]

Dear All,
I would like write program in c# to measure distance between two dark squares:

I read that i have to count pixels, so could You tell me:

1. How recognize end of dark area to start (stop) count pixels?
2. How to show arrow with distance?

Best Regards,
Martin

[andrew.kirillov]

Hello,

1. How recognize end of dark area to start (stop) count pixels?

In grayscale images, black pixels usually have value 0, but white pixels have value 255. So you may need write some code which searches for a white gap between black areas (255 values between 0 values).

To simplify things, you may invert your image and then use BlobCounter from AForge.NET framework.

2. How to show arrow with distance?

Draw it. Use some drawing API.

[Requan]

Hi Andrew;
Thanks for help and sorry for my basic questions.
My camera has 640x480 res, i converted on grayscale and counted blobs - blobs lenght showed = 90 - it is correct?
One blob = one pixel?

Code: Select all

             Grayscale filter = new Grayscale(0.2125, 0.7154, 0.0721);
             Bitmap grayImage = filter.Apply(image);

            //pictureBox1.Image = grayImage;
           
            // create and configure blob counter
            BlobCounter blobCounter = new BlobCounter();

            blobCounter.MinHeight = 1;
            blobCounter.MinWidth = 1;
            blobCounter.FilterBlobs = true;
            blobCounter.ObjectsOrder = ObjectsOrder.Size;

            blobCounter.ProcessImage(grayImage);
            Blob[] blobs = blobCounter.GetObjectsInformation();

         
            for (int i = 0, n = blobs.Length; i < n; i++)
            {
               
            }


To check value of blobs i will have to use: blobs.getvalue in FOR loop?

Best Regards,
Martin

[andrew.kirillov]

Where do you use invert filter? As you may find in documentation, BlobCounter can find white objects (none black) on black background. Background must be black. Everything else is treated as object (blob).

One blob = one pixel?

No. One blob = one object = collection of pixels which have some connection (8 directions are used for connection).

[Requan]

Thanks for Your comments and patience. I appreciate it.
Sorry i thought that grayscale is the same as invert.
I corrected the code:

Code: Select all

            Invert filter = new Invert();
            // apply the filter
            filter.ApplyInPlace(image);
            BlobCounter blobCounter = new BlobCounter();

            blobCounter.MinHeight = 32;
            blobCounter.MinWidth = 32;
            blobCounter.FilterBlobs = true;
            blobCounter.ObjectsOrder = ObjectsOrder.Size;

            blobCounter.ProcessImage(image);
            Blob[] blobs = blobCounter.GetObjectsInformation();

            for (int i = 0, n = blobs.Length; i < n; i++)
            {

               
            }


1) Now background is black. On picture i have two squares and program detected 1 blobs - it is correct?

I read documentation but i have no idea how put value of pixels to the list. In blobcounter we have methods: GetBlobsTopAndBottomEdges, GetBlobsLeftAndRightEdges and GetBlobsEdgePoints.

2)Which i should to use it?

3) How i use it? like this: List<IntPoint> edgePoints = blobCounter.GetBlobsEdgePoints(blobs[i])? and check value in list?

Best Regards,
Martin

[andrew.kirillov]

On picture i have two squares and program detected 1 blobs - it is correct?

No, it is not correct. You should get 2 blobs - one per each white square. If you got only one, then you may need to try using Threshold filter to make sure you have only black and white pixels. When you get 2 blobs, just check their coordinates (see Rectangle property of Blob). Using some trivial math you will get distance between squares from those coordinates.

[Requan]

Thanks Andrew. Now i detect object:

I also detect corners, but when i used rectangle properties and drow a line (please look at picture) program showed line in strange position. Where i made mistake?

Code: Select all

g.DrawLine(pen, blobs[0].Rectangle.X, blobs[0].Rectangle.Y, blobs[1].Rectangle.X, blobs[1].Rectangle.Y);


Could You advice how i should to do? maybe use GetBlobsLeftAndRightEdges, or measure distance between corners?

Best Regards,
Martin

[Requan]

Andrew,
I know You don't have time to answer on my silly question, but please answer me only wy when i us higher resolution then 800x600 (eg full HD - my camera can take it) and convert image to bitmap grayscale etc i get image with offset position (it shifted form orginal)

Code: Select all

                VideoCaptureDevice videoSource = form.VideoDevice;
                Size sz = new Size();
                sz.Height = 1080;
                sz.Width = 1920;
                videoSource.DesiredFrameSize = sz;


[andrew.kirillov]

I don't know why your image is shifted. Grayscale filter is not supposed to shift anything. You can actually check it by examining initial color image and result grayscale image. Maybe your camera shifts something, when it is configured to capture in high resolution. Maybe there is something wrong in the way you draw the image. Do you draw it on your own? If so check all coordinates carefully.