Bug#894462: paraview: edges are blotted [regression]

[Francesco Poli]

On Thu, 04 Jan 2024 12:18:21 +0100 Drew Parsons <dparsons at debian.org>
wrote:
[...]
> The png generated by the procedure in this bug looks fine to me, using
> current paraview (5.11).  It's slightly blurry but no more than you'd
> expect for a png file (it's raster image format, not a vector image
> format, you can't expect to main high resolution if you zoom into the
> pixels).

Hello and thanks for following up on this bug report.

I appreciate that you took the time to check whether the bug is still
reproducible with current paraview (5.11.2+dfsg-6+b1 in both testing
and unstable, at the time of writing).

However, I disagree with your conclusion.

I have just checked again.
What follows is the procedure to obtain the attached images.

First of all, (re-)enable the use of FXAA:

 • select Settings... from the Edit menu
 • in the "Render View" tab, check "Use FXAA"

Then, follow the steps described in the [original bug report] and save
the screenshot as "with_FXAA.png".

[original bug report]: <https://bugs.debian.org/894462#5>

After that, disable the use of FXAA:

 • select Settings... from the Edit menu
 • in the "Render View" tab, uncheck "Use FXAA"

Finally, follow the steps described in the original bug report and save
the screenshot as "without_FXAA.png".

Image "with_FXAA.png" is more than slightly blurry, I think it looks
blotted. More than one would expect from PNG file.
I acknowledge that PNG is indeed a raster image format (and not a
vector image format), but the PNG format can definitely do better than
this.
Compare with "without_FXAA.png", which looks better, in my humble
opinion. Granted, it has no anti-aliasing, but, at least, it does not
look weirdly blotted...

In conclusion, I don't think the issue is due to limitations in raster
image formats.
The issue seems to be due to flaws or limitations in the FXAA
algorithm, which does a commendable attempt to anti-alias the lines,
but, unfortunately, creates an unsightly "blot" effect on the edges,
especially on their intersections, when viewed from a distance.

> 
> Can you confirm paraview 5.11 is meeting your image quality
> expectations?

Only if I disable FXAA (which, by the way, is enabled by default, but
can luckily be disabled in the settings!).

> 
> As far as I can tell, we can close this bug now.

I think the bug report should be kept open.

Could you please forward it upstream, instead?
Thanks for your time and dedication!


-- 
 http://www.inventati.org/frx/
 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
 GnuPG key fpr == CA01 1147 9CD2 EFDF FB82  3925 3E1C 27E1 1F69 BFFE
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