Use color names from image

Question

I would like to check what colors are present in the image. This will be stored in the database and used for the search form. (red = 1, green = 1, blue = 0, yellow = 1, black = 1, white = 1, etc.)

img = Magick::Image.read('phosto-file.jpg').first img = img.quantize(10 h = img.color_histogram pp h {red=12815, green=18494, blue=15439, opacity=0=>13007, red=44662, green=47670, blue=51967, opacity=0=>18254, red=17608, green=43331, blue=48321, opacity=0=>11597, red=21105, green=25865, blue=39467, opacity=0=>10604, red=15125, green=36629, blue=22824, opacity=0=>10223, red=52102, green=42405, blue=10063, opacity=0=>12928, red=39043, green=28726, blue=40855, opacity=0=>7728, red=10410, green=8880, blue=7826, opacity=0=>13795, red=25484, green=25337, blue=24235, opacity=0=>7351, red=44485, green=12617, blue=11169, opacity=0=>14513} 

How do I convert 10 values ​​to color names? red, green, NOMATCH, yellow, black, white, etc. All you need is a crude color name - not LimeGreen, but green, etc.

Sincerely. Asbjorn Morell

Answer 1

If you can represent all the colors you are looking for in the same number format that ImageMagick returns. You can then compare the RGB values ​​to find what it is closest to.

So, for example, if you have a histogram value (assuming 255 values ​​for each color, YMMV)

 { red => 10, green => 255, blue => 10 } 

Then you can compare it with each of

 { red => {red => 255, green => 0, blue => 0}, green => {red => 0, green => 255, blue => 0}, blue => {red => 0, green => 0, blue => 255} } 

So, if you add the difference between all the elements you get

 { red => 510, green => 20, blue => 510, } 

So you can clearly see that the color is close to green

UPDATE: added solution in Ruby

 def compare_color(color_val) colors = { :red => [255,0,0], :green => [0,255,0], :blue => [0,0,255] } difference = {} def compare_array(a1,a2) total = 0 a1.each_index do |x| total += (a1[x]-a2[x]).abs end total end colors.each do |color,hex| difference[color] = compare_array(color_val,hex) end closest = difference.sort{|a,b| a[1] b[1]}.first [closest,difference] end p compare_color([10,255,10]) # [[:green, 20], {:red=>510, :green=>20, :blue=>510}] 

Answer 2

A simple way would be to have a list of RGB values ​​and their corresponding names, and you would choose the closest matching color (within the margin of error). For basic colors, even a very simple sum of the differences in each of the RGB channels can give workable results, although I suspect that you will run out of the color name if the data looks like this. You can find a list of color names on the net, perhaps this will help to remove one such list. (Note that they usually expect a range of 0..255 for colors, so you will need to convert the data from a wider range to your data.)

Converting RGB values ​​to hue, saturation and brightness and using them to generate names, for example, may be a slightly more complicated way. “dark red” when the hue is red, the saturation is high enough not to be gray, and the brightness is low (but not low enough to be black).

Answer 3

You may find this blog post interesting. It accurately explains how to solve your problem. I also released ColorNamer gem , which gives you the closest named color from an RGB value or an HTML hash. You can also use any Color object.