Extracting Unique RGB Values from List-CodePudding

I created a list of RGB values for an image (let's say it's 3D_image, composed of 3D_image_slice). I want to extract the unique RGB values from it, but I'm running into problems.

rgb_values_unique = [] 
for 3D_image_slice in 3D_image:
for y in range(3D_image_slice.shape[0]):
    for x in range(3D_image_slice.shape[1]):
        if 3D_image_slice[y, x] not in rgb_values_unique:
            rgb_values_unique.append(3D_image_slice[y, x])

I was thinking of using np.unique, but that doesn't apply to lists. Is there another way to find unique values within a list?

CodePudding user response：

You have a couple of easy options; one is to create a unique list of strings (I don't love this since it changes the datatype, but it's look something like this):

rgb_values_unique = set()
for 3D_image_slice in 3D_image:
  for y in range(3D_image_slice.shape[0]):
    for x in range(3D_image_slice.shape[1]):
     rgb_values_unique.add("-".join(3D_image_slice[y, x])

print(rgb_values_unique)
# {"r0-g0-b0", "r1-g1-b1", ...}

#which you could convert back into numbers like this:
result = [[int(j) for j in i.split("-")] for i in rgb_values_unique]

What I'd probably do is leverage the uniqueness of a dictionary:

rgb_values_unique = {}
for 3D_image_slice in 3D_image:
  for y in range(3D_image_slice.shape[0]):
    for x in range(3D_image_slice.shape[1]):
      r,g,b = 3D_image_slice[y, x]
      rgb_values_unique .setdefault(r, {}).setdefault(g, []).append(b)

print(rgb_values_unique)
# {r0: {g0: [b0, b1, b2]}, {g1: ...

Which you can then turn into a unique listing as follows:

result = [(r,g,b) for r,v in rgb_values_unique.items() for g, b_list in v.items() for b in b_list]

CodePudding user response：

u can use sets to save only unique values:

rgb_values_unique = {} 
for 3D_image_slice in 3D_image:
    for y in range(3D_image_slice.shape[0]):
        for x in range(3D_image_slice.shape[1]):
            rgb_values_unique |= 3D_image_slice[y, x]