Re: [Matplotlib-users] Bug: Image transparency varies periodically for imshow(img, aspect='auto') at high magnification

[Darren D. <dd...@co...>]

Hi Joel,

On Thursday 01 February 2007 11:09:11 am Joel Hedlund wrote:
> I believe I've found a bug in matplotlib which manifests after
> imshow(img, aspect='auto') when only a small portion of the image is
> displayed, e.g: when (xmax-xmin) << img.shape[1]. The effect of the bug
> is that the transparency for the entire image seems to vary, seemingly
> as a periodic funtion of (xmax-xmin). Explicitly setting the alpha
> channel for each pixel has no effect.
>
> The attached script generates a random image of a certain size, and
> plots it in four different subplots. The only thing that differs between
> the subplots are slight variations in x_max. The four subplots are labeled:
>
> 1) The background image is visible.
> 2) The background image is not visible!
> 3) The background image is faded!
> 4) The background image is again visible!
>
> which reflects the actual result on my system. As the subplots are
> scaled (for example by resizing the window), the intensity then varies
> in a periodic manner in each of the subplots.
>
> The expected result is of course that the background should be fully
> visible in all subplots.

I can verify this behavior, more or less. I observe that the figure.dpi rc 
setting influences the results (I tried 86.23 and 200).