F8.10 Project: send a picture

Build the program from the brief. Print the 24 picture lines, then uncompressed: 768 bits (calculated), compressed: <n> characters, and lossless: True. Send the message if it has 200 characters or fewer.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

img = camera_image(32, 24)

The hint students can ask for: Turn the camera frame into rows of two characters, compress each row, and join the rows with a separator the receiver can split on. Check the message fits the radio limit, and prove it is lossless by decoding your own message and comparing.

A solution

from bugbot import *
connect()
def rle_encode(text):
    out = ""
    count = 1
    for i in range(1, len(text)):
        if text[i] == text[i - 1]:
            count = count + 1
        else:
            out = out + str(count) + text[i - 1]
            count = 1
    return out + str(count) + text[-1]

def rle_decode(code):
    out = ""
    number = ""
    for ch in code:
        if ch.isdigit():
            number = number + ch
        else:
            out = out + ch * int(number)
            number = ""
    return out
img = camera_image(32, 24)
picture = []
for row in img:
    line = ""
    for r, g, b in row:
        line = line + ("#" if (r + g + b) / 3 < 128 else ".")
    picture.append(line)
for line in picture:
    print(line)
print("uncompressed:", 32 * 24, "bits")
message = "/".join(rle_encode(line) for line in picture)
print("compressed:", len(message), "characters")
rows = [rle_decode(part) for part in message.split("/")]
print("lossless:", rows == picture)
if len(message) <= 200:
    send(message)
else:
    print("too big")

Any program that meets the task's checks is marked correct in the simulator; this is one way, not the only way.