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Python - How to sort a list of colors based on the color "distance" from the original color in 3D (r, g, b) space?

Here are the basic steps for the application that I am writing in Python:

  • Create a list of random colors
  • Create a mapping of each of these colors indexed by this color distance to the “source color” in 3D space (r, g, b). (For example, orange (255, 150, 0) is closer to red (255, 0, 0) than blue (0, 0, 100). Currently, I have a list of format tuples (distance, color).
  • Sort the list of tuples based on the calculations I calculated (from lowest to highest).
  • Get a list of sorted colors

Here is my function, and I get the following error: TypeError: the object 'int' does not have the attribute '_getitem _' in the string sorted_by_dist = sorted (colorMap, key = lambda tup: tup [0])

# Sorts a list of colors according to distance from the source color def sort_colors(colors, source): colorMap = () sortedColors = list() for i in range(len(colors)): dist = dist_3d(colors[i], source) colorMap = colorMap + (dist, colors[i]) sorted_by_dist = sorted(colorMap, key=lambda tup: tup[0]) for (d, c) in sorted_by_dist: sortedColors.append(c) return sortedColors

Assuming my dist_3d () function is correct and returns an integer value (it is and does), what am I doing wrong? I do not understand.

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2 answers

You build your colorMap as a large one-dimensional tuple, with the first index being int . This way your lambda is passed int , and then you try to index it.

You probably need a list of tuples:

 colorMap = [] ... dist = dist_3d(colors[i], source) colorMap.append((dist, colors[i]))

As for the approach to sorting colors, I actually used the kdtree module for this, loaded with all RGB tuples. Then I can set the specified color tuple for the N nearest colors:

 from kdtree import KDTree colors = [(10,10,10),(250,50,5),(100,50,20)] query_color = (175, 25, 50) tree = KDTree.construct_from_data(data) # query the 2 closest colors nearest = tree.query(query_point=query_color, t=2)
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The error is due to the fact that tup is int . __getitem__ is the name of the [] operator.

But it looks like all your function does is sorts the list of colors, depending on the distance from some reference color. And you already have dist_3d . Given that it works, sorting colors is a lot easier. Sort them in place:

 colors.sort(key=lambda color: dist_3d(color, reference_color))

or as a new list:

 sorted_colors = sorted(unsorted_colors, key=lambda color: dist_3d(color, reference_color))

It is not necessary that all of these tuples and loop, etc. in your function, as I can say.

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