Blank png: x.png does not set the alpha/transparency info correctly !

[jypeter]

I have finally understood why I was getting completely blank png images, as reported in #845 after trying to open the png in different programs: it seems that somehow the image is there, but the alpha channel value is set to 0 for all the pixels (according to gimp's color picker tool), which make the image seem completely transparent

Am I the only person having this problem ???

@doutriaux1 , could you check the properties of the saved png you generate?

When I run the following commands

import numpy as np, vcs
id100 = np.identity(100)
x = vcs.init()
x.plot(id100)
x.png('test_default_png')

I get the following completely blank/transparent image!

If I remove the alpha/transparency with ImageMagick (http://www.imagemagick.org/Usage/masking/#alpha_off), I get a png with the visible image I want! Of course, I'd like to have directly a png I can see :)

convert -alpha off test_default_png.png test_default_png-noalpha.png

[doutriaux1]

@jypeter we changed the default back to have a non-transparent backaground, you can control this in your version via the foloowing parameter:
x.png(bla, draw_white_background = True)
or
x.png(bla, ignore_alpha=True)

[jypeter]

Pfff, how am I supposed to guess that, it's not even in help(x.png) :/

I have tried the 4 different combinations of draw_white_background set to True or False and ignore_alpha set to True or False and

• I confirm I get an image with ignore_alpha=True. It has a white background, regardless of the value of draw_white_background
• I never get an image with ignore_alpha=False, regardless of the value of draw_white_background

draw_white_background does not seem to have any effect and I have not been able to get an image on a transparent background

I'm using the 2.0.0 tag UV-CDAT

[doutriaux1]

not in your version but in master draw_white_background works.