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Each element of the matrix determines the intensity of the corresponding pixel.
For convenience, most of the current digital files use integer numbers between 0 (to indicate black, the color of minimal intensity)
and 255 (to indicate white, maximum intensity), giving a total of 256 different levels of gray.
This number of different levels of gray is reasonable to work with images in WEB pages, for instance.
However, there are certain specific applications that need more levels of gray in order to reproduce
the image with more details and avoid rounding errors in numerical calculations, as is the case of medical images.
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1.
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The applet below is interactive. Leave the mouse pointer still for a few moments on a pixel to see its numerical value.
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2.
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You may define a function f in the input field below.
Pressing the “Update!” button, the applet will replace
each pixel of gray level c by a pixel of gray level f(c).
If f (c) is greater than 255, then the new pixel will be set to a gray level equal to 255.
If f (c) is less than 0, then the new pixel will be set to a gray level equal to 0.
To specify a function defined by parts, use the command “If()”. For instance,
if you type
If(c > 50, 0, 255)
in the input field, then the following function f will be defined: f(c) = 0 for c > 50, otherwise f(c) = 255.
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3.
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To select one of the seven images available, click on the corresponding icon.
Challenge: using an appropriate function f, try to discover the secret message in the last image.
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