[Octave-bug-tracker] [bug #44794] image package: imtransform should use 0 instead of NaN for the default extrapolation value

[Pantxo Diribarne]

Update of bug #44794 (project octave):

                  Status:                    None => Confirmed              

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Follow-up Comment #3:

The process of transforming the image is as follows:
* Define a transform: in this example it is defined by the user who provides a
direct transform (here a pure rotation matrix).
* infer the reverse transform.
* infer the size of the output image using the direct transform: here rotating
the image by 45deg makes the output image necessarily larger than the input
one (widthout = ceil (witdthin * sqrt (2))). 
* For each pixel in the output space, use the reverse transform to infer the
corresponding coordinates in the input space.
* use interp2 in the input space to find the  interpolated value of the pixel
in the output space.

When a pixel in the output space is not defined in the input space, its value
(gray level here) will be replaced by a fixed EXTRAP value (see "help
interp2"). Solving this bug is just a matter of changing the default value of
the "fillvalue" property in imtransform.m. 

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