Visible disc

Started by raymoh, November 25, 2018, 05:46:30 am

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raymoh

I'm into astronomical art (as an amateur) and want to be as accurate as possible. I wanted to create a visible (star) disc lower than the sun's (0.5 degrees) but it seems thats not possible. If I choose a lower diameter Terragen renders always the 0.5 degrees of the suns disc, despite the slider goes to 0.0000...something. If the disc is lower than 0.005 degrees Terragen jumps suddenly to a disc near 0 degrees. That behavior seems to me a bug. It would be nice to fix that.
Beauty is in the eye of the beholder.

cyphyr

Works for me.
Are you using the slider or typing it in?
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raymoh

November 25, 2018, 10:29:31 am #2 Last Edit: November 25, 2018, 10:33:14 am by raymoh
It doesn't matter.
The diameter will be constant at about 0.4 degrees and jumps to nearly 0 at 0.005 degrees.
Background: I set the disc's diameter in relation to the image size. For example the image size is 1920x1080 and Terragen computes a FOV of about 60 degrees, so the sun's apparent diameter (0.5 degrees) will be about 16 pixel wide. This pixel-diameter is I work with. It seems more accurate to me. And in this context I can't reach my desired 0.2 degrees (or 7 pixels)...:-(

macOs Mojave 10.14.1 on an iMac Pro; Terragen 4.3.18
Beauty is in the eye of the beholder.

WASasquatch

Are you vieweing through atmosphere? TG has a light focusing issue in atmosphere and clouds.
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raymoh

I noticed that, but for my "tests" I used an untouched atmosphere and reduced all glow amount and glow power to a minimum. I also reduced the sunlight strength to obtain a clear defined sun disc.
Beauty is in the eye of the beholder.

WASasquatch

November 25, 2018, 02:33:27 pm #5 Last Edit: November 25, 2018, 02:48:23 pm by WASasquatch
Interesting. It'd be easier to see the issue with an example TGD in this case. You may also have better luck with a light source.

Have you tried something like this?
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Matt

November 25, 2018, 09:08:45 pm #6 Last Edit: November 25, 2018, 09:11:33 pm by Matt
Try turning off "anti-aliasing bloom" on the render node's Filter tab. Turning this off might cause a jagged edge to the star due to the extremely bright values. Anti-aliasing bloom is designed to overcome this, but has the side effect of making the star appear larger. If you render a larger image, this side effect will be smaller relative to the image size.

Just because milk is white doesn't mean that clouds are made of milk.

raymoh

November 26, 2018, 05:05:44 am #7 Last Edit: November 26, 2018, 05:10:39 am by raymoh
Hi Matt
Your input was great!
Without Anti-Aliasing-Bloom the sun disc's diameter are much more accurate, but it work well only with the Narrow Cubic Pixel Filter.
Mitchell-Netravali and Catmull-Rom are rendering a dark ring around the disc.

[attach=1]
Disc Test +Bloom/Catmull-Rom
[attach=2]
Disc Test -Bloom/Catmull-Rom
[attach=3]
Disc Test -Bloom/Narrow Cubic
Beauty is in the eye of the beholder.

WASasquatch

The disc will always have a slightly rough appearance without high detail as well as it has no curve and is just a solid disc.
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raymoh

Do you refer to the Pixel Filter(s)? (Narrow Cubic vs Catmull-Rom)
Beauty is in the eye of the beholder.

WASasquatch

Quote from: raymoh on November 26, 2018, 01:27:47 pm
Do you refer to the Pixel Filter(s)? (Narrow Cubic vs Catmull-Rom)


Honestly I rarely use other AA methods due to artefacting.
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raymoh

November 26, 2018, 02:02:45 pm #11 Last Edit: November 26, 2018, 02:05:02 pm by raymoh
Quote from: WASasquatch on November 26, 2018, 01:40:10 pm
Honestly I rarely use other AA methods due to artefacting.

Sorry when I insist: Does that mean you are working mostly with the Narrow Cubic Filter?
Beauty is in the eye of the beholder.

WASasquatch

Quote from: raymoh on November 26, 2018, 02:02:45 pm
Quote from: WASasquatch on November 26, 2018, 01:40:10 pm
Honestly I rarely use other AA methods due to artefacting.

Sorry when I insist: Does that mean you are working mostly with the Narrow Cubic Filter?


Yes. I rarely change it. Sometimes I'll use Catnum-Roll for close shots of surfaces with very fine low-level detail as it helps create definition between shapes instead of muddling them, but usually not with atmospherics or objects.
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Oshyan

The black artifacts are inherent to those particular filters, yes (they are "negative lobes", far too much detail can be found here :D https://en.wikipedia.org/wiki/Ringing_artifacts and here: http://www.yafaray.org/community/forum/viewtopic.php?f=14&t=4744 ).

- Oshyan

WASasquatch

Quote from: Oshyan on November 26, 2018, 05:54:47 pm
The black artifacts are inherent to those particular filters, yes (they are "negative lobes", far too much detail can be found here :D https://en.wikipedia.org/wiki/Ringing_artifacts and here: http://www.yafaray.org/community/forum/viewtopic.php?f=14&t=4744 ).

- Oshyan


Never seen that second article. Thanks Oshyan.
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