Re: [Veusz-discuss] Transparency on images with nan values and log scaling

[Jeremy Sanders]

Hi Mark

On 04/05/17 04:22, Mark Durre wrote:

I’m displaying images with nan values; normally these show as
transparent and display the background color of the graph. However, when
I change the scaling to log the blank fill become the lowest value color
on the colormap, which could be anything, and is also problematic when
the lowest value on the scale is relevant (causing confusion). My
solution has been to create another dataset with log values and display
that with linear scaling, while also having the original image on the
same graph but hidden, then having a colorbar linked to the old image.
Complicated I know! i.e. on the one graph


I've hopefully fixed this in this change. I'll put it in the new release 
shortly.


https://github.com/jeremysanders/veusz/commit/5cdde90367051ae74d3965c56efad4a18638928d

Jeremy

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[Veusz-discuss] Transparency on images with nan values and log scaling

[Mark Durre]

Hi Jeremy,

I’m displaying images with nan values; normally these show as transparent and 
display the background color of the graph. However, when I change the scaling 
to log the blank fill become the lowest value color on the colormap, which 
could be anything, and is also problematic when the lowest value on the scale 
is relevant (causing confusion). My solution has been to create another dataset 
with log values and display that with linear scaling, while also having the 
original image on the same graph but hidden, then having a colorbar linked to 
the old image. Complicated I know! i.e. on the one graph

Image1 – original data, scaled log, hidden
Image2 – log data, scaled linear
Colobar1 – linked to Image1

Can there be a change so that nan values when displayed on log scale are 
transparent?

I attach an example plot file, just toggle the “Hide” flag on image1 to see 
what I mean.

Thanks and cheers,

Mark Durré
Ph.D. Student
Centre for Astrophysics and Supercomputing
Swinburne University of Technology
PO Box 218, Hawthorn
Victoria 3122, Australia
Email: mdu...@swin.edu.au




Logscale_nan_problem.vsz
Description: Logscale_nan_problem.vsz
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