The functions in this section perform various geometrical transformations of 2D images. That is, they do not change the image content, but deform the pixel grid, and map this deformed grid to the destination image. In fact, to avoid sampling artifacts, the mapping is done in the reverse order, from destination to the source. That is, for each pixel
:math:`(x, y)` of the destination image, the functions compute coordinates of the corresponding "donor" pixel in the source image and copy the pixel value, that is:
extrapolation of non-existing pixels. Similarly to the filtering functions, described in the previous section, for some
:math:`(x,y)` one of
:math:`f_x(x,y)` or
:math:`f_y(x,y)` , or they both, may fall outside of the image, in which case some extrapolation method needs to be used. OpenCV provides the same selection of the extrapolation methods as in the filtering functions, but also an additional method ``BORDER_TRANSPARENT`` , which means that the corresponding pixels in the destination image will not be modified at all.
:math:`\left<f_x, f_y\right>` can be an affine or perspective transformation, or radial lens distortion correction etc.), so a pixel values at fractional coordinates needs to be retrieved. In the simplest case the coordinates can be just rounded to the nearest integer coordinates and the corresponding pixel used, which is called nearest-neighbor interpolation. However, a better result can be achieved by using more sophisticated `interpolation methods <http://en.wikipedia.org/wiki/Multivariate_interpolation>`_
, where a polynomial function is fit into some neighborhood of the computed pixel
:math:`(f_x(x,y), f_y(x,y))` and then the value of the polynomial at
:math:`(f_x(x,y), f_y(x,y))` is taken as the interpolated pixel value. In OpenCV you can choose between several interpolation methods, see
:func:`remap` from one representation to another. The following options ( ``(map1.type(), map2.type())``:math:`\rightarrow```(dstmap1.type(), dstmap2.type())`` ) are supported:
:math:`\texttt{(CV\_32FC1, CV\_32FC1)} \rightarrow \texttt{(CV\_16SC2, CV\_16UC1)}` . This is the most frequently used conversion operation, in which the original floating-point maps (see
:func:`remap` ) are converted to more compact and much faster fixed-point representation. The first output array will contain the rounded coordinates and the second array (created only when ``nninterpolation=false`` ) will contain indices in the interpolation tables.
:math:`\texttt{(CV\_32FC2)} \rightarrow \texttt{(CV\_16SC2, CV\_16UC1)}` . The same as above, but the original maps are stored in one 2-channel matrix.
:param angle:The rotation angle in degrees. Positive values mean counter-clockwise rotation (the coordinate origin is assumed to be the top-left corner)
:param dst:Destination image. It will have the same size as ``map1`` and the same type as ``src``
:param map1:The first map of either ``(x,y)`` points or just ``x`` values having type ``CV_16SC2`` , ``CV_32FC1`` or ``CV_32FC2`` . See :func:`convertMaps` for converting floating point representation to fixed-point for speed.
:param borderMode:The pixel extrapolation method, see :func:`borderInterpolate` . When the \ ``borderMode=BORDER_TRANSPARENT`` , it means that the pixels in the destination image that corresponds to the "outliers" in the source image are not modified by the function
:param dst:Destination image. It will have size ``dsize`` (when it is non-zero) or the size computed from ``src.size()`` and ``fx`` and ``fy`` . The type of ``dst`` will be the same as of ``src`` .
***INTER_AREA** resampling using pixel area relation. It may be the preferred method for image decimation, as it gives moire-free results. But when the image is zoomed, it is similar to the ``INTER_NEAREST`` method
The function ``resize`` resizes an image ``src`` down to or up to the specified size.
Note that the initial ``dst`` type or size are not taken into account. Instead the size and type are derived from the ``src``,``dsize``,``fx`` and ``fy`` . If you want to resize ``src`` so that it fits the pre-created ``dst`` , you may call the function as: ::
:param flags:A combination of interpolation methods, see :func:`resize` , and the optional flag ``WARP_INVERSE_MAP`` that means that ``M`` is the inverse transformation ( :math:`\texttt{dst}\rightarrow\texttt{src}` )
:param borderMode:The pixel extrapolation method, see :func:`borderInterpolate` . When the \ ``borderMode=BORDER_TRANSPARENT`` , it means that the pixels in the destination image that corresponds to the "outliers" in the source image are not modified by the function
:param flags:A combination of interpolation methods, see :func:`resize` , and the optional flag ``WARP_INVERSE_MAP`` that means that ``M`` is the inverse transformation ( :math:`\texttt{dst}\rightarrow\texttt{src}` )
:param borderMode:The pixel extrapolation method, see :func:`borderInterpolate` . When the \ ``borderMode=BORDER_TRANSPARENT`` , it means that the pixels in the destination image that corresponds to the "outliers" in the source image are not modified by the function
