When a spacecraft records an image from space, that image, comprised of thousands of pixels (short for picture elements, the dots that make up a picture), is changed into a radio signal and sent to Earth. Here on Earth the radio signal is changed back into a picture. In this exercise, students will experiment with a method similar to that used for producing a satellite-generated image. Students will generate their images on graph paper. Each square on the graph paper represents one pixel or picture element.

Some of the French painters of the 19th century could be said to have created early versions of pixel images. Look at paintings by French post-impressionist painters Georges Seurat and Paul Signac, who pioneered pointillism, a style in which the painter uses dots of pure color rather than brushstrokes to create an image. Seurat's Sunday Afternoon on the Island of La Grande Jatte (1886) is probably the most famous example of this style. Students will create their own pointillist images (and satellite pixel images).

### Materials

• graph paper
• pens or pencils

### Communicate like a satellite!

1. To introduce the idea of how pixels combine to produce a recognizable image, look at a computer monitor or a television screen with a magnifying lens.

Newspaper photos and television images are also made up of pixels. To illustrate this use a photocopier to enlarge a newspaper photograph to several times its size.

1. Pair up students. Have one student create a picture on graph paper by shading in certain boxes.
2. Have the second student try to recreate the image as follows:

The artist ("satellite") scans the picture from the left beginning with the first square in row 1.

If the space is blank, the student says, "Zero."

If the space is shaded, the student says, "One."

The artist proceeds this way square by square across the row to the last square in row 1 and then scans each row in the same way down the page.

The second student ("the receiving station") records the scan on her graph paper. Every time she hears the word "One," she shades in that square. When she hears the word "Zero," she leaves the square blank.

1. After the students have finished reading and recording all the rows, they compare images.

Are they the same, or was the message garbled?

1. Repeat the activity, but reverse the students' roles.