Creating stars using light sources

Started by Denis Sirenko, May 15, 2018, 12:56:33 PM

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Denis Sirenko

Hi guys!

There is a problem. I want a very small light source, about 1 pixel in size (on my scale it corresponds to the radius of the light source of 10 meters), which would give a good starburst (bloom) effect. The problem is that the light source remains small in size only for a limited range of brightness. This brightness I do not have enough for the appearance of a starburst (bloom) effect. But when I try to increase the brightness of the source, this leads to a visual increase in its radius. Satisfactory starburst appears only when the radius of the source on my image reaches about 4 pixels.
This is already too big value for my purposes.

1) Why is the apparent size of a light source dependent on its brightness?

2) How can I solve this problem?

There is a limitation: I can not increase the starburst (bloom) parameter, as this will result in the appearance of a glow where I do not need it (on a nebula that is nearby).

Here's how it looks (Note: all the stars have the same settings, as indicated; one of the stars on the lower right is not relevant to this issue):

[attachimg=1]

Oshyan

I think this is just a limitation in how Terragen's various glows and post effects (e.g. starburst) work. Possibly made worse by large scales in a space scene.

- Oshyan

WAS

I think it's the scales and the bloom masking the object.

If you use super large scales, you'll see it's a luminous sphere, and even at these scales, the light is emitted from a source point in the center of this object.

So at these scales it's hard to see the object over it's glow.

Kadri


Have you tried with higher Antialiasing values?

Matt

This is probably caused by using "anti-aliasing bloom", or a soft pixel-reconstruction filter, or both. For the sharpest results you could try the Narrow Cubic pixel filter with anti-aliasing bloom turned off. With some of the other pixel filters you need to keep anti-aliasing bloom turned on to prevent "ringing" around the bright stars, but this contributes to the enlargement of the object. Narrow Cubic allows you to turn it off.

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

Denis Sirenko

Thanks for the responses, guys!

I want to answer everyone, but I will immediately say that Matt's advice helped.

Quote from: Oshyan on May 15, 2018, 03:20:29 PM
I think this is just a limitation in how Terragen's various glows and post effects (e.g. starburst) work. Possibly made worse by large scales in a space scene.

Do you mean "Bloom" as a "glows"? The fact is that on the first frame you can see that the Bloom and Starburst are off, but the star is still of a larger radius than I should see, and at the same time the circle of the star is even. As if that's the way it should be. On the other hand, you are probably right about the scale in the space scene. On a smaller scale, I did not encounter such a problem, or simply it was not so noticeable.

Quote from: WASasquatch on May 15, 2018, 04:49:43 PM
I think it's the scales and the bloom masking the object.
If you use super large scales, you'll see it's a luminous sphere, and even at these scales, the light is emitted from a source point in the center of this object.
So at these scales it's hard to see the object over it's glow.

Almost the same as I said to Oshyan. The effect occurs even when there are no post effects such as Bloom or Starburst.

Quote from: Kadri on May 15, 2018, 06:14:56 PM
Have you tried with higher Antialiasing values?

Yes, I tried, it almost does not affect. Although some other changes seem to occur when regulating AA. But this is not a decrease in the star, but an influence on the evenness of the edge (visible without post effects) or even on the brightness of the Bloom (only for small values of AA). In addition, I believed that the light source should always be visible, even if it is very small. But it turned out that with small AA values this is not always visible. On some frames, when I do the animation, some stars just disappear! Although they were not found using raytracing, and the positions were specified for Terragen explicitly.

Quote from: Matt on May 15, 2018, 06:38:07 PM
This is probably caused by using "anti-aliasing bloom", or a soft pixel-reconstruction filter, or both. For the sharpest results you could try the Narrow Cubic pixel filter with anti-aliasing bloom turned off. With some of the other pixel filters you need to keep anti-aliasing bloom turned on to prevent "ringing" around the bright stars, but this contributes to the enlargement of the object. Narrow Cubic allows you to turn it off.

Yes, Matt, thank you. This turned out to be the solution, I had the selected mode Narrow Cubic, but the Anti-alizing bloom was turned on. I turned off the bloom, the stars diminished. However, this is still not enough for me. Let's just say, now my stars are already "almost good", but not "super" :)

Here the result:

[attachimg=1]

By the way, is there no way to remove these flashes when the star is exactly on the edge of the frame? For example, can I somehow create a black frame 1 pixel thick at the edge of the frame before the post-effect (Bloom or Starburst) is applied? Otherwise, I suppose I will have to abandon Starburst inside Terragen and apply post-effects in a third-party application, which I do not really want to do, because I like Starburst, which Terragen offers.

KlausK

Perhaps animate the Starbust down to 0 right before the light leaves the frame? Tedious, I think. But perhaps that helps?
CHeers, Klaus
/ ASUS WS Mainboard / Dual XEON E5-2640v3 / 64GB RAM / NVIDIA GeForce GTX 1070 TI / Win7 Ultimate . . . still (||-:-||)

Denis Sirenko

KlausK, thanks, but then all other stars also will turn off starburst. This will cause all stars to become noticeably darker each time one of them passes the edge of the frame. I will get a general flicker.

But your advice pushed the idea that I can turn off the stars, that is, reduce their brightness before passing the edge of the frame. But yes, it's so tiring that this variant did not even visit my head. Moreover, I will increase the number of stars.

luvsmuzik

Just something I noticed and wondered about in your starfield KlausK...what does animating the 4D noise do in your starfield? Something one would maybe not notice when doing your setup from scratch.

Denis Sirenko

I solved my problem with flashes. Just needed to use a thin crop on the perimeter of the frame :)

WAS

Bless your heart for manually placing all those light sources.

KlausK

You`re right. My idea was shortsighted. Didn`t think of the fact that it is a render setting and not a per light thingie.
Good you solved it so easily by cropping. CHeers, Klaus.
/ ASUS WS Mainboard / Dual XEON E5-2640v3 / 64GB RAM / NVIDIA GeForce GTX 1070 TI / Win7 Ultimate . . . still (||-:-||)

WAS

Quote from: Denis Sirenko on May 17, 2018, 01:12:10 PM
I solved my problem with flashes. Just needed to use a thin crop on the perimeter of the frame :)

I think this should be fixed in later updates. Shouldn't need a crop. It's similar to filters in Photoshop when applied on boundaries of a image with that has no extended hidden canvas. When working on "higher quality images" it's always best have have a unconstricted canvas so effects can "span" off the viewport.

Denis Sirenko

Quote from: WASasquatch on May 18, 2018, 02:06:51 PM
It's similar to filters in Photoshop when applied on boundaries of a image with that has no extended hidden canvas. When working on "higher quality images" it's always best have have a unconstricted canvas so effects can "span" off the viewport.

Yes, I also thought about the blur algorithm (for example, Gaussian) in Photoshop, which "paints" the image outside the canvas, so that the application of the filter becomes possible. As a color for the continuation of the image outside the canvas, Photoshop takes the color that was on the edge. In the case of a simple Gaussian blur, this is often justified, since this filter has no function to work only with bright light sources, but there is a need to "look beyond the edge". So we can avoid using a spare canvas along the edges without noticeable artifacts when using a Gaussian blur.

But Bloom and Starburst are a slightly different situation. Here I want to clarify that this is only my vision of this task. Specialization of these post-effects (Bloom and Starburst) - work specifically with bright sources that are visible in the frame. This is an imitation of the lens effect (internal scattering by the radiation detector), for which only what is in the frame is important. Behind the scenes for these post-effects should be taken blackness, and not some kind of "supposed scene" (which is simply necessary for a Gaussian blur). But it's in my opinion, maybe I'm missing some details.

WAS, you talk about a canvas on the edge. Unfortunately, this is not a solution to the problem, because the flash will still arise, it just will appear further from the final edge of the canvas. However, its effect can extend almost to the whole image, especially if the light source was bright enough. This means you need to create a canvas with a margin comparable to the size of the final image itself.

WAS

#14
Quote from: Denis Sirenko on May 19, 2018, 03:55:12 AM
Quote from: WASasquatch on May 18, 2018, 02:06:51 PM
It's similar to filters in Photoshop when applied on boundaries of a image with that has no extended hidden canvas. When working on "higher quality images" it's always best have have a unconstricted canvas so effects can "span" off the viewport.

Yes, I also thought about the blur algorithm (for example, Gaussian) in Photoshop, which "paints" the image outside the canvas, so that the application of the filter becomes possible. As a color for the continuation of the image outside the canvas, Photoshop takes the color that was on the edge. In the case of a simple Gaussian blur, this is often justified, since this filter has no function to work only with bright light sources, but there is a need to "look beyond the edge". So we can avoid using a spare canvas along the edges without noticeable artifacts when using a Gaussian blur.

But Bloom and Starburst are a slightly different situation. Here I want to clarify that this is only my vision of this task. Specialization of these post-effects (Bloom and Starburst) - work specifically with bright sources that are visible in the frame. This is an imitation of the lens effect (internal scattering by the radiation detector), for which only what is in the frame is important. Behind the scenes for these post-effects should be taken blackness, and not some kind of "supposed scene" (which is simply necessary for a Gaussian blur). But it's in my opinion, maybe I'm missing some details.

WAS, you talk about a canvas on the edge. Unfortunately, this is not a solution to the problem, because the flash will still arise, it just will appear further from the final edge of the canvas. However, its effect can extend almost to the whole image, especially if the light source was bright enough. This means you need to create a canvas with a margin comparable to the size of the final image itself.

From what I see, the flashes extend the whole frame from their source. You can plainly see the "starburst" shape in the frame if you pause video and step forward/back.

That being said, a hidden extended canvas could easily be created to mask the exceeding limit of these shapes. For example, hidden canvas 3/4 larger than the base frame will hide border flashes. This same approach is used in Knoll Light Factory I believe when dragging lights off frame, and even shows the extended canvas (example image provided).

And gain, similar approaches can be used by Matt or other developers to make a starburst plugin that works correctly with boundaries, where they span off frame, and fade to nothing instead of a large frame hack. Light sources already have keying.

I wouldn't talk about it if it wasn't a used approached in photoshop, after effects, and many many other programs. In general this seems like a bug as that's now how light sources act with lenses. In past movies (like 90s) they've used similar effects but it may be due to issues like this rather than realism.