All of the pictures which you are viewing on the computor are 8-bit digital images, which means that they have 256 colors (2^8). The image below illustrates this principle. Digital images are tables of numbers, which in this case range from 0 to 255. Note that the "bright" squares (called pixels) have high number values (ie. 200 to 255), while the "dark" pixels, have low number values (ie. 50-100). This image is an extreme closeup of a satellite image of West Hancock. The dark region is a stream valley, which has low reflectance, while the bright area is a gravel pit, which has high reflectance. The satellite sensor records the reflectance in its field of view, and then scales the signal to an 8-bit number (0 to 255).
Click here for a hands on demonstration of producing color images.
A small white box should appear
after you clicked on the word "here".
Place the cursor in the white box
and hit the "e" key.
A large color edit panel will pop
up. Find the part of the color edit panel that looks like this:
Place the cursor arrow on the end
of one of the color arrows (red, green, or blue). Hold down the left mouse
button and move the arrow. When you release the arrow, the color of the
small box will change.
By changing the red, green and blue
values, you can make any color.
Try to produce the following colors:
Important: After finshing with the demo
put the cursor in the small box and hit "q". This will kill the demo.
A small satellite image of Houghton
will pop up on your screen.
Put the cursor in the image, hold
down the left mouse button, and drag the mouse to define a box.
After selecting a box, release the
center button, and hit the "c" key (for cut). That piece will be cut out of
the image. Use the "<" key to shrink the image and the ">" key to enlarge
it.
If you want to return the image to
its normal size, hit the "n" key.
To paste the image back together, hit
the "u" key.Important: After finishing the demo, put the
cursor in the box and hit "q". This will kill the demo.
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