Artur Wieczorek 097625de52 Fixed rescaling of wxImage ...

When wxImage is rescaled with wxIMAGE_QUALITY_BILINEAR, wxIMAGE_QUALITY_BICUBIC or wxIMAGE_QUALITY_BOX_AVERAGE algorithm then for proper interpolation there is necessary to uniformly (linearly) map entire pixel range in the new image to the entire pixel range in the current image, i.e. pixels positions (integer values) in range [0..newDim-1] has to be mapped to "virtual" pixel positions (not necessary integer values) exactly in the range [0..oldDim-1].
[0..oldDim-1] range of target mapping is required because for proper interpolation every "virtual" pixel has to be located between two physical pixels in the current image.
Thus scaling ratio used to find corresponding pixels in the current image should be (oldDim-1)/(newDim-1) and not oldDim/newDim (which is used now).
When image is e.g. upsampled oldDim/newDim ratio then some new rightmost/botommost pixels are mapped to old pixels > (oldDim-1) and their values are improperly interpolated (in the current implementation their positions are just truncated to (oldDim-1) to bypass the problem and upsampled image looks like it was shifted left/up). The larger scaling ratio the effect is more visible.

Note:
Because reference images used currently in the unit tests were created with improper scaling there is necessary to upload new reference images created with fixed scaling.

Closes #17594

2016-07-22 23:00:33 +02:00

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