Re: [matplotlib-devel] more fun with animation

[Abraham S. <ab...@cn...>]

Thanks! Great catch. Sadly, I have been bitten by this before, but had 
completely forgotten about it. I've switched to just doing vmin=0, 
vmax=1, as I know the range before hand.

Abe

Ken McIvor wrote:

> On Aug 30, 2005, at 10:29 PM, John Hunter wrote:
>
>> I suggest you follow pick through set_data and make_image in the image
>> module to see if you can sort out what is going wrong.  Alternatively,
>> if you post an example then I can take a look.
>
>
> I've done Abraham's work for him this time, and attached an example 
> which demonstrates behavior that he *may* be seeing.
>
> The problem is that the minimum and maximum values of the image are 
> determined every time the image is asked to draw itself (in 
> matplotlib.image.AxesImage.__draw()).  I assume that what's happening 
> is that the colors aren't fading down the color ramp as the values 
> decay, but are rather staying constant or blurring a little.
>
> This happens because the color ramp is being applied across the 
> current minimum and maximum of the data, rather than across some 
> absolute scale.  The solution to this (see the attached script for the 
> example) is to specify a vmin and vmax, which will pin the top and 
> bottom of the color ramp to those values:
>
>     # assuming z0 is the initial MxN array that is being decayed...
>     z_min = min(nx.minimum.reduce(z0))
>     z_max = max(nx.maximum.reduce(z0))
>     image = axes.imshow(z0, vmin=z_min, vmax=z_max)
>
> As an aside: I'd love to hear if anyone knows of a nicer way to get 
> Numeric to give you the minimum value of a matrix.
>
> Ken