Get the percentage usage of every colour in an image

Question

I have this one working but it is so damn slow on jpeg images and also needs some changing.

I need to know the individual colours in an image (with a tolerance of +/- 1 for RGB) and the % of the image that is that colour.

so if an image was black and white it would say something like White : 74% Black : 26%

The code below works like I said but I need to add a tolerance system as well and I have no idea on how I would do that.

private Dictionary<string, string> getPixelData(Bitmap image)
{
    Dictionary<string, string> pixelData = new Dictionary<string, string>();
    //int col, row;
    //int r, g, b;
    Color pixel;

    double offset = 0.000001;
    int hmm = (image.Height * image.Width);
    double current = 0;
    offset = 100 / double.Parse(hmm.ToString());// 0.01;// 100 / (image.Height * image.Width) * 10000;

    try
    {
        for (int i = 0; i < image.Height; i++)
        {
            for (int j = 0; j < image.Width; j++)
            {
                current = current + offset;
                pixel = image.GetPixel(i, j);                        
                pixelData.Add(i + "," + j, (pixel.R.ToString() + " " + pixel.G.ToString() + " " + pixel.B.ToString()));
                pBarprocess.Value = int.Parse(Math.Floor(current).ToString());
                pBarprocess.Update();
                Application.DoEvents();
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Unable to parse image " + ex);
    }

    return pixelData;
}

And the other function

private void btnProcess_Click(object sender, EventArgs e)
{
    pBarprocess.Value = 0;
    pBarprocess.Enabled = false;
    Bitmap foo = Bitmap.FromFile(@txtFileName.Text) as Bitmap;
    Dictionary<string, string> pixelData = new Dictionary<string, string>();

    lblProcess.Text = "Processing pixel map";
    pixelData = getPixelData(foo);

    lblProcess.Text = "Calculating Density";
    lblProcess.Update();

    var distinctList = pixelData.Values.Distinct().ToList();

    Console.WriteLine("DL = " + distinctList.Count);
    double offset = 100 / double.Parse(distinctList.Count.ToString());
    double current = 0;

    foreach (var value in distinctList)
    {
        IEnumerable<string> query = pixelData.Values.Where(fruit => fruit == value);
        double perc = (double.Parse(query.Count().ToString()) / double.Parse(pixelData.Count.ToString())) * 100;
        Console.WriteLine(value + " = " + query.Count() + "(" + perc + "%)");
        txtAnalysis.Text = "Colour " + value + " : " + query.Count() + " (" + perc.ToString() + "%)\r\n" + txtAnalysis.Text;
        txtAnalysis.Update();
        pBarprocess.Value = int.Parse(Math.Floor(current).ToString());
        pBarprocess.Update();
        Application.DoEvents();
    }

    lblProcess.Text = "Finished.";
    pBarprocess.Value = 0;
    pBarprocess.Enabled = false;
}

Answer 1

GetPixel is not really a fast way to access image data. Use the LockBits method.

EDIT:

Well you're doing a lot of things with strings. Building the pixelData Dictionary that way is pretty useless, why don't you process the distinct colors right away? Color is an immutable struct, so that's a good key for our dictionary already.

Dictionary<Color, int> frequency = new Dictionary<Color, int>();
for (int i = 0; i < image.Height; i++) {
  for (int j = 0; j < image.Width; j++) {
    pixel = image.GetPixel(i, j);
    if (frequency.ContainsKey(pixel)) frequency[pixel]++;
    else frequency.Add(pixel, 1);
  }
}

// and finally
int totalPixels = image.Width * image.Height;
foreach (var kvp in frequency) {
  Console.WriteLine("Color (R={0},G={1},B={2}): {3}", kvp.Key.R, kvp.Key.G, kvp.Key.B, kvp.Value / (double)totalPixels);
}

And that should do it, except when you want to make it even faster and use LockBits instead of GetPixel.

Some other observations:

int hmm = (image.Height * image.Width);
double offset = 100 / double.Parse(hmm.ToString());

You're using a very strange and slow way of casting from int to double. You can just write double offset = 100 / (double)hmm; and it's the same (you could also write 100.0 and not 100 and the compiler will create a double for you so you don't need to cast hmm).

This made me laugh:

IEnumerable<string> query = pixelData.Values.Where(fruit => fruit == value);

Why fruit!? Seems like you copied this from somewhere.