For an index,
if the type is not FLOAT,
final conversion consists of masking the index with the value given
Table 4.6;
if the type is FLOAT,
then the integer index is converted to a GL float data value.
For a component,
each component is first clamped to 
.
Then, the appropriate conversion formula from Table 4.7 is applied to
the component.
Table 4.6: Index masks used by ReadPixels . Floating point data are
not masked.
Table 4.7: Reversed component conversions - used when component data
are being returned to client memory. Color, normal, and depth
components are converted from the internal floating-point
representation (f) to a datum of the specified GL data type (c) using
the equations in this table. All arithmetic is done in the internal
floating point format. These conversions apply to component data
returned by GL query commands and to components of pixel data returned
to client memory. The equations remain the same even if the
implemented ranges of the GL data types are greater than the minimum
required ranges. (Refer to table 2.2)