black-and-white image of the Crab Nebula
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.
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.
image of the Crab Nebula