A message arrives from the far side of the station, where the screens are down for repairs.
"Can you send us a piece of today's best snapshot?" the engineers ask. "We only have pencils and graph paper."
Rocket groans. "How do you send a picture with no screen?"
Raven is already writing a grid of numbers. "We send the brightness values. They shade the squares and rebuild it."
Nova hovers over her shoulder. "Then the picture travels as data," she says. "Just as it does inside any computer."
Rocket grabs a pencil. "I want to try decoding one first."
You will decode a snapshot from brightness values, then encode a snapshot of your own.
Then you will measure three features from your grid. Those features will feed Sky Sorter next.
On paper, darker shading stands for a brighter pixel, so the comet shows up clearly against white paper.
A real snapshot card is a much bigger grid. This 5 by 5 grid is a zoomed-in crop around the comet's head, so most of the tail runs off its edge.
| Comet crop | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 |
|---|---|---|---|---|---|
| Row 1 | 0 | 0 | 0 | 0 | 0 |
| Row 2 | 0 | 0 | 0 | 60 | 180 |
| Row 3 | 30 | 60 | 120 | 200 | 255 |
| Row 4 | 0 | 0 | 0 | 60 | 180 |
| Row 5 | 0 | 0 | 0 | 0 | 0 |
A feature is one measured property of a snapshot. Sky Sorter will use three.
Brightness: the value of the brightest pixel, from 0 to 255.
Size: how many pixels wide the object is. Count the pixels of 100 or more across its widest row.
Today you measure only the crop. On the full card, the comet's glow and tail make it much wider.
Streak: yes if bright pixels make a straight line all the way across the grid, and no if not.
| What the lab shows | True or false? |
|---|---|
| A picture can travel as numbers and be rebuilt on paper. | ? |
| The comet crop has a streak. | ? |
| Brightness, size and streak are three features of a snapshot. | ? |
| Two different people can rebuild the same picture from the same values. | ? |
Great lab work. Tomorrow you will build Sky Sorter's first feature table.