How to efficiently count the number of unique colors in Java

edit

Can you be a little more explicit? What is unique color?

Well what you should do is the following

1. First decide what you define as a unique color. This means you need to define a R G and B range for each unique color.
2. Threshold any given image in steps over the threshold regions. If a white blob pops up in your binary result than you can decide that the colour is retrieved in the image.
3. Finally store a vector with all the colors that are retrieved, even using masking to color in a black image size frame to show the different regions.

It's much simpler... let's rephrase the question in "How to efficiently count colors in a Mat object in Java", without "unique"... I know there's cvCountNonZero, but I have to split the channels... etc, or I could iterate every pixels. I would like a simple way to count colors like in Photoshop fo example. Thanks.

I would not suggest you to iterate, because it is slow, here is the documentation of split and using cvCountNonZero, I do not think is really what you want, can you give a link of Photoshop color counter?

@costa_974, even if you just count colors. Then the combination is still endless if you do not predefine what you see as colors. With an 8 bit image and 3 channels RGB you have multiple thousands of comibnations. Keep in mind that color is NOT the same for a PC as for a human eye!

c# code: public static int CountImageColors(string fileName) { int count = 0; HashSet<Color> colors = new HashSet<Color>(); Bitmap bmp = null;

if (File.Exists(fileName))
{
    try
    {
        bmp = new Bitmap(fileName);
        if (bmp != null)
        {
            for (int y = 0; y < bmp.Size.Height; y++)
            {
                for (int x = 0; x < bmp.Size.Width; x++)
                {
                    colors.Add(bmp.GetPixel(x, y));
                }
            }
            count = colors.Count;
        }
    }
    catch 
    {
        throw;
    }
    finally
    {
        colors.Clear();
        bmp.Dispose();
    }

OpenCV doesn't support C# probably you are using a wrapper? You should then address forum related to that wrapper and not this one.

ok... you guys are too smart! i'm not able to be clear! the c# code is just an example! how can I do the same in opencv? I just want to count the colors in a image!

public int countColors(byte[] img_buffer, int channels) {

    Set<Integer> set =  new HashSet<Integer>();
    int img_buffer_length = img_buffer.length;

    for (int i = 0; i < (img_buffer_length - channels); i += channels)
    {
         int pixelVal = 0;
         for (int j = 0; j < channels; j++) {
            pixelVal += (img_buffer[i + j] << (8 * j));
         }
         set.add(pixelVal);
    }

    int r = set.size();

    return r;

}