A packing line carries lemons along a grey conveyor belt, and a batch of white ping-pong balls has been tipped in by mistake. A colour camera watches the belt, and under the factory lights it records these values:
| red | green | blue | |
|---|---|---|---|
| lemon | 230 | 220 | 40 |
| ping-pong ball | 235 | 230 | 225 |
| belt | 120 | 120 | 120 |
To save memory, the camera will keep only one of its three channels and throw the other two away. The sorting software then sees a single grayscale grid, one number per pixel, and has to tell lemon, ball and belt apart from that number alone.
Which channel should the camera keep?
Select all that apply.