Question

I am currently working on a project involving manipulation of binary images on pixel level (thinning, clustering etc.). Many of the algorithms used involve checking the attributes of neighboring pixels. A pixel object defined as:

Public class pixel
{
int x, y;
int NumberOfNeighbours;
int ConnectivityNumber;
int ClusterNumber;
}

I can create a list containing all the pixels in the image for processing them sequentially but I want to link each of the pixels in the list to their position on a grid to efficiently get properties of its neighbor pixels.

For example, if I have a map[7,7] with 9 pixels [A to I] in the map,
https://i.stack.imgur.com/UwHTn.jpg
and I want to check the value of the ClusterNumber of each neighbour of each pixel. It seems very inefficient to run through the list 8 times to find the neighbors of each pixel and it would be easier to use the grid to just check the neighbors. Is there a way to reference a pixel in the grid so that I can access its properties as a neighbor of the current pixel in the list? I’ve thought about creating a int[,] map = new int[width,height] containing the indexes of the pixels in the list, but this creates a problem when a pixel is removed from the list and map would need to be updated every time a pixel is removed from the list.

Alternatively, is there a way I can link/point to the neighbors of a pixel in the class itself such that (schematically) I could access a neighbor’s properties

//list[0].NeighborE  == null
//list[0].NeighborNE == B
//list[0].neighborN  == null
//...
//list[1].NeighborE  == G
//list[1].NeighborNE == D
//list[1].NeighborN  == C
//list[1].NeighborNW == null
...
if (list[i].NeighborE.ClusterNumber > 2)
    list[i].ClusterNumber = 2;

Any advice/guidance would be appreciated.

Answer 1

Public class pixel
{
    int x, y;
    int NumberOfNeighbours;
    int ConnectivityNumber;
    int ClusterNumber;

    //neighbors:
    Pixel _neighborN;
    Pixel _neighborNE;
    ...
    Pixel _neighborNW;
}

Here you need to assign all neighbors pixels during initialization. If current pixels is near the edge, you just assign it to null. But do not forget to check null-values when you operate with them.