"Download plot as png" returns damaged heatmaps, if it is a lot of values

[PlatonB]

Plotly 3.6.1, Fedora 28, Firefox 65.

A screenshot of a big heatmap made by "Download plot as png" is incorrect:

The correct version made by Firefox Screenshots:

[jonmmease]

Hi @PlatonB, thanks for the report.

Could you share the code you're using to make this? Or better yet, a minimal example with synthetic data that shows the problem.

We'll need to work out a reproducible example and open a report with the Plotly.js project at https://github.com/plotly/plotly.js/issues

[PlatonB]

Hello, @jonmmease !
Example with synthetic data:

import random, plotly as py, plotly.figure_factory as ff
z = [[round(random.random(), 2) for cell_index in range(300)] for row_index in range(300)]
heatmap = ff.create_annotated_heatmap(z, xgap=1, ygap=1, colorscale='Greens')
heatmap['layout']['annotations'] = []
py.offline.plot(heatmap)

"Download plot as a png":

Firefox Screenshots:

[jonmmease]

Hi @PlatonB,

I think the issue might be the figure size. Clicking save snapshot doesn't automatically use the current figure size. So my guess is that the figure is expanded to a larger size when you take the firefox snapshot than the default plotly download png size. Try setting the figure.layout.width and figure.layout.height to something larger and see if you get better results.

Alternatively, you might consider setting xgap and ygap to 0 when the resolution of the heatmap is approaching the resolution of the plot area of the resulting png image.

[PlatonB]

Hello, @jonmmease !
I made width x height equal 1920x1080, and set xgap and ygap as 0. Indeed it works that way. The heatmap saved as png is visible (albeit slightly blurred). It's a bit frustrating that this is not the default behavior.

[jonmmease]

For discussion of figure size when using the export button see plotly/plotly.js#1576.

It alright if we close this here in favor of that issue?

[PlatonB]

Thanks!
OK.