I have a picture:
size of 1000x1000 white with random black dots. (It may contain a black square (size 50x50))
Is there an easy way to know if the picture contains a black square (size 50x50)? I thought of scanning every pixel of the picture and if a black pixel was found, scan the one next to him till I get a 50x50 square or till I get a white pixel and keep scanning. but it will have to scan over a million pixel (if he hasn't found the square).
Thats the basically the code (no need to complete it, as I said before, it will take way too much time to scan it. million times if the whole picture is white and a lot more according to the number of black pixels.)
for (int i = 0; i < pic.Width; i++)
{
for (int j = 0; j < pic.Height; j++)
{
if (pic.GetPixel(i, j) == Color.Black)
{
//Search for the entire square at that area
}
}
}
And yes, time is important (thats why I don't want to get pixel over a million times). Any ideas?
Like the Boyer-Moore string searching algorithm, if the item you are looking at is not part of what you are looking for, you can skip the whole size of the what you are looking for. In your case, you can check to see if a given pixel is black. If it's not, you can skip forward 50 pixels. If it is, you have a small box to look for your black square in.
In this case, though, you may not need anything so complicated. I'm guessing that if your algorithm is too slow it's because you're calling the GetPixel function a million times, and that is the slow part. If you can get your pixels into a 2D array, your algorithm will probably go fast enough to not need to be rewritten.
Assuming that you're using a System.Drawing.Bitmap check out the LockBits documentation to see a small sample that includes copying a bitmap to a 1D array for super-fast access.