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How are the color pictures made?

Positive black-and-white image of the Crab Nebulaitive black-and-white                 image of the Crab Nebula</FONT>
Positive black-and-white image of the Crab Nebula

black and white palette

The cameras on the HST are not color cameras, they take only black & white pictures. The cameras represent the brightness of the scene by varying numerical values. These values can be represented by shades of gray, in positive or negative. There are fundamentally two ways to make color images from the black & white pictures. A color may be assigned to each numerical value, exactly analagous to painting-by-number. These colors are arbitrary, but they may be selected from different groups or palettes. The palette bar beneath each image represents the range of numerical values in the image, from the minimum at the left to the maximum at the right.

The different palettes can be used to emphasize specific parts of the image to highlight a particular feature. The eye is more sensitive to slight variations in color than to variations in gray, so the color scale may show faint details with more contrast.

Thermal image of the Crab Nebula
Thermal image of the Crab Nebula

thermal palette

Negative image of the Crab Nebula
Negative image of the Crab Nebula

negative palette
Spectrum image of the Crab Nebula
Spectrum image of the Crab Nebula

spectrum palette

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