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Color in Digital Images

Image of a rubber duck with complete set of red, green, and blue colors.

You see color on things around you because light shines into your eye, is received by the cones and rods of your retina, and converted to electrochemical signals that are then processed through your brain. A digital camera detects color because light shines on sensors in your camera which are sensitive to red, green, and blue. The number of sensors in the camera will define the highest resolution possible for that camera. A traditional film based camera records an image onto a chemically treated plastic. Digital cameras record the red, green, and blue intensities for each pixel into a numerical file – the values of color and position of the pixel are defined with numbers. A number of different file types are used to compress the data so the file takes up a minimal amount of computer memory. To display the image on the computer screen, the computer takes the red intensity value for a particular pixel from the file and shines the red component of the pixel at that amount at that place on the computer screen. It does the same thing for the other two primary colors (green and blue) for every pixel in the image.

Seeing Only One Color of Light

When we talk about seeing only one color we are not referring to the condition known as color blindness. People who are colorblind have difficulty distinguishing between certain colors, for example red and green, but they are still capable of perceiving light of both colors. What we are talking about is if you could only see the small range of light wavelengths that is called “red”. You would be unable to perceive the spectrum of light including orange, yellow, green, blue, and violet.

In satellite images, each color is data of the image that provides specific information. By turning off all of the light that is not red, we can look solely at the information that red light provides. If we were physically only able to see the range of light that is red, it would appear more like a black and white image than a red and black image. The use of black and white to view such information allows us to make out details and differences in shade and intensity more easily.

Image of duck with only red light displayed in black and white
Image of rubber duck with only red light displayed.
Image of rubber duck with only red light displayed

Image of duck with only red light displayed in
black and white.

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