Re: [matplotlib-devel] blurry images at native resolution with images.BboxImage: patch to fix

[Benjamin R. <ben...@ou...>]

On Thursday, October 13, 2011, Daniel Hyams <dh...@gm...> wrote:
> I was playing around with images.BboxImage, and found that if I displayed,
say a 100x100 image at its native resolution (exactly 100x100 pixels on the
plotting window), it was blurred.  This is because of the interpolation
jumping in and interpolating when it is not needed.
> This might not be the best way to fix, but it does work....in matplotlib
1.0.0, it is image.py around line 1102 (this is BboxImage.make_image).  Just
after numrows and numcols is set in that routine, do
>  if (r-l) == numcols and (t-b) == numrows:
>             im.set_interpolation(0)
> As you can see, all this does is just flip the interpolation off if the
size of the image is the same size that it is about to be rendered as...and
the regular interpolation is used otherwise.
>
> I do apologize for the lack of a proper patch, but for little things like
this I think a word description works as well or better; I need to sit down
and both learn git and set of a development environment for matplotlib, but
after reading through the docs on the web site about it, decided that would
take me more time than I had at the moment.
>
> In context:
>     def make_image(self, renderer, magnification=1.0):
>         if self._A is None:
>             raise RuntimeError('You must first set the image array or the
image attribute')
>         if self._imcache is None:
>             if self._A.dtype == np.uint8 and len(self._A.shape) == 3:
>                 im = _image.frombyte(self._A, 0)
>                 im.is_grayscale = False
>             else:
>                 if self._rgbacache is None:
>                     x = self.to_rgba(self._A, self._alpha)
>                     self._rgbacache = x
>                 else:
>                     x = self._rgbacache
>                 im = _image.fromarray(x, 0)
>                 if len(self._A.shape) == 2:
>                     im.is_grayscale = self.cmap.is_gray()
>                 else:
>                     im.is_grayscale = False
>             self._imcache = im
>             if self.origin=='upper':
>                 im.flipud_in()
>         else:
>             im = self._imcache
>         # image input dimensions
>         im.reset_matrix()
>         im.set_interpolation(self._interpd[self._interpolation])
>
>
>         im.set_resample(self._resample)
>         l, b, r, t = self.get_window_extent(renderer).extents
#bbox.extents
>         widthDisplay = (round(r) + 0.5) - (round(l) - 0.5)
>         heightDisplay = (round(t) + 0.5) - (round(b) - 0.5)
>         widthDisplay *= magnification
>         heightDisplay *= magnification
>         numrows, numcols = self._A.shape[:2]
>
>         if (r-l) == numcols and (t-b) == numrows:    # <-----------------
add this
>             im.set_interpolation(0)
#<-------------- and this
>         # resize viewport to display
>         rx = widthDisplay / numcols
>         ry = heightDisplay  / numrows
>         #im.apply_scaling(rx*sx, ry*sy)
>         im.apply_scaling(rx, ry)
>         #im.resize(int(widthDisplay+0.5), int(heightDisplay+0.5),
>         #          norm=self._filternorm, radius=self._filterrad)
>         im.resize(int(widthDisplay), int(heightDisplay),
>                   norm=self._filternorm, radius=self._filterrad)
>         return im
>
> --
> Daniel Hyams
> dh...@gm...
>

Daniel,

imshow() does take an "interpolation" kwarg, where you can specify "nearest"
for pre v1.1.0 versions and "none" (not None) in the recent release.
 "nearest" would be close to what you want, while "none" is exactly what you
want.

Personally, I don't think it would be a good idea to automatically turn
interpolation off on such a specific set of conditions, but I could be
wrong.  I would rather have the user explicitly state their interpolation
intentions.

Ben Root