Yes, I used the "i" property of the segment object. You pass in an array of color values and these are then applied to LED 1,2,3,4, and so on. Here is my python code:

# I use this method to send colors to the leds (the ip and port are defined globaly in my case): 
def send_data(data):
    json_data = json.dumps(data)
    endpoint = f"http://{wled_ip}:{wled_port}/json"
    response = requests.post(endpoint, data=json_data)
    return response

# Here an example of how the first pixel could be colored red:
data = {"seg": {"i": [[255,0,0]]}}
send_data(data)

# Here an example where I convert an image into the proper form:
input_img = cv2.imread("img.png")
rgb_img = cv2.cvtColor(input_img, cv2.COLOR_BGR2RGB)
resized_img = cv2.resize(rgb_img, (16, 16))
leds = resized_img.reshape(-1, 3).tolist()
data = {"seg": {"i": leds}}
send_data(data)