Determine Dominant Color of Picture

Question

I am trying to come up with an algorithm to determine the dominant color in an image (either taken from a devices camera or by selecting an existing photo in the photo library). I have written an iOS 8 application in Swift that can grab the RGB value of each pixel in the image, but I don't really know what to do from there.

For pixels that have a distinct dominant color, say RGB(230, 15, 30), it's pretty easy to determine the dominant color. However, I don't really know what to do for pixels that have RGB values where 2 of the 3 values are similar, say RGB(200, 215, 30).

My original thought was to keep 3 counters (one for each color) and add each pixels corresponding RGB values to that counter. At the end I would divide each counter by the total number of pixels and the max of the 3 values would be the dominant color. However, like I mentioned before, when the results are close to each other I can't say that one color necessarily dominates the other.

Just looking for some thoughts and suggestions

Answer 1

I came up with this problem a few weeks ago, and having read many posts talking about it, I found the best method is Hierarchical Quantization presented by this post: http://aishack.in/tutorials/dominant-color/. Also, I have implemented it in python: https://github.com/wenmin-wu/dominant-colors-py . You can install it with pip:pip install dominantcolors and use it as following:

from dominantcolors import get_image_dominant_colors
dominant_colors = get_image_dominant_colors(image_path='/path/to/image_path',num_colors=3) 

Answer 2

An idea:

1. First step is to reduce the number of colors, for example "Color Quantization using K-Means". In the example from the link, the number of colors was reduced to 64 from 96K.

2. Second step is to calculate the ratio for every color and pick the biggest value.