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.. _ref-dwt2:
.. currentmodule:: pywt
=================================================
2D Forward and Inverse Discrete Wavelet Transform
=================================================
Single level ``dwt2``
~~~~~~~~~~~~~~~~~~~~~
.. autofunction:: dwt2
The relation to the other common data layout where all the approximation and
details coefficients are stored in one big 2D array is as follows:
::
-------------------
| | |
| cA(LL) | cH(LH) |
| | |
(cA, (cH, cV, cD)) <---> -------------------
| | |
| cV(HL) | cD(HH) |
| | |
-------------------
PyWavelets does not follow this pattern because of pure practical reasons of simple
access to particular type of the output coefficients.
Single level ``idwt2``
~~~~~~~~~~~~~~~~~~~~~~
.. autofunction:: idwt2
2D multilevel decomposition using ``wavedec2``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. autofunction:: wavedec2
2D multilevel reconstruction using ``waverec2``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. autofunction:: waverec2
2D coordinate conventions
~~~~~~~~~~~~~~~~~~~~~~~~~
The labels for "horizontal" and "vertical" used by ``dwt2`` and ``idwt2``
follow the common mathematical convention that coordinate axis 0
is horizontal while axis 1 is vertical::
dwt2, idwt2 convention
----------------------
axis 1 ^
|
|
|
|--------->
axis 0
Note that this is different from another common convention used in computer
graphics and image processing (e.g. by matplotlib's ``imshow`` and functions in
``scikit-image``). In those packages axis 0 is a vertical axis and axis 1 is
horizontal as follows::
imshow convention
-------------------
axis 1
|--------->
|
|
|
axis 0 v
|
