Image data types and what they mean
===================================

.. note::

   This is a preliminary design document.

In ``scikits.image``, we assume the following dtype ranges:

=========== ================
Data type   Range 
=========== ================
uint8       0 to 255
uint16      0 to 65535
float       0 to 1
int8        -128 to 127
int16       -32768 to 32767
=========== ================

Input types
-----------

Functions may choose to support only a subset of these data-types.  In
such a case, the input will be converted to the required type (if
possible) and a warning message printed to the log if a memory copy is
needed.  Type requirements should be noted in the docstrings.

The following utility functions are available to developers and
users:

(*Tentative list only -- not implemented yet*)

=============== =======================================
Function name   Description   
=============== =======================================
img_as_float    Convert to 64-bit floating point repr.
                Scaled to 0/1.
img_as_uint     Convert to 16-bit uint repr.
                Scaled to 0-65535.
img_as_int      Convert to 16-bit int repr.
                Scaled to -32767 to 32768.
=============== =======================================

Wherever possible, functions should try to handle input
without explicit conversion (e.g., there is no need to
force values to a specific type for doing a convolution;
a plotting function, on the other hand, needs to know the
range of the input).

Output types
------------
The output type of a function is determined by the function author,
and documented for the benefit of the user.  While this requires the
user to explicitly convert the output to whichever format is needed,
it ensures that no unnecessary data copies take place.

A user that requires a specific type of output (e.g., for display
purposes), may do::

  out = img_as_uint(sobel(img))
  plt.imshow(out)
