The Color of Mars

What color is Mars? That seems a basic question, but to scientists it is a challenge to accurately depict the color of this alien landscape. Since people have not directly observed the Martian surface, we rely on images sent back from robotic explorers. The cameras on these devices ""see"" into a different window of electromagnetic radiation, which means scientists must tweak the displayed visual image to best reproduce the actual scene. Most likely, earlier images of the Martian surface displayed a surface that is redder than the landscape's true color.

By Michael DiSpezio|Wednesday, November 24, 2004


Color Correcting

Your visual system is constantly updating and correcting colors your eyes detect. This process ensures that colors appear the same and unchanged even when viewed under different lighting conditions. For example, in an environment with a reddish cast, your visual processing applies an automatic color correction to the scene. It reduces the reddish hues, while pumping up the saturation of other colors.

Camera (film or digital)
Magazine with full-color picture

1. Obtain a film or digital camera. If you are using a digital camera, make sure that any automatic color balance is turned off.

2. Obtain a magazine with full-color pictures. Select an image that contains a variety of bright colors.

3. Photograph this picture outside so that it is only illuminated by sunlight.

4. Bring the picture indoors. Make sure no sunlight spills into the room. Illuminate the page with incandescent light (bulbs with filaments). Take a photograph of the page. Do not use a flash.

5. Take another photograph of the picture. This time use a flash.

6. Bring the page into a room that is lit only by florescent light. Make sure that sunlight or the light from an incandescent lamp does not spill into the room.

7. Take a photograph of the page lit by only florescent light. Then, take a second photograph using a flash.

8. Obtain photographic prints or printouts of these images. Compare them side-by-side. Are the colors consistent from image to image? What might account for any observed differences?

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1. Contrast the appearance of colors photographed in natural sunlight with the same colors under incandescent light. What differences do you observe? (In incandescent light, the colors are less vibrant and have a reddish tint.)

2. Contrast the appearance of colors photographed in natural sunlight with the same colors under florescent light. What differences do you observe? (In florescent light, the colors are less vibrant and have a green-blue tint.)

3. How does an electronic flash affect the appearance of a subject’s color? (The flash produces a color balanced light that more closely resembles the color shades you observe in natural sunlight.)



Earthly Cache of Martian Images
Perform a Web search for images of the Martian surface. Do any of the images you uncover offer a 3D view of this alien landscape? If so, how is the 3D effect produced?  Do you need any special viewing device to observe the 3D effect? If so, explain how it works. (The red/blue glasses extract independent right and left images and isolate them to each eye. The brain does the rest, constructing a composite image that has three dimensionality based on the differences in the two images.)

Upside Down Confusion
Examine the image on page 67. Describe what you see. Which are the lowest parts of this landscape? Which are the highest elevations? Now, spin the page upside down. Again examine the image. What happened?  Why did your perception of what you observed change? Explain how similar ambiguous images might confuse researchers who interpret images transmitted back from robotic explorers.

Rusty Red
The red color of the Martian surface is attributed to the rusted iron found in the Martian soil. You can produce your own version of this soil color with some iron filings. Place the filings in a container filled with salt water. After several days, examine the filings. Describe their change in appearance.


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