ode</b>.

<p>An image with bit depths below 8 will be converted to 8 bits when
read, and an image with bit depths between 8 and 16 bits will be
converted to 16 bits.  As an example, a 2-bit PNG file contains only the
pixel values 0, 1, 2, and 3.  These will be converted to 0, 85, 170,
and 255, respectively, in order to fill the dynamic range of the 8-bit
image that is returned.

<p><b>Exceptional Situations:</b>
<p>Signals
an <a href="http://www.lispworks.com/documentation/HyperSpec/Body/e_error.htm#error">