Author Topic: bluesky  (Read 989 times)

Offline majidkaviani

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bluesky
« on: November 22, 2015, 07:08:10 AM »
hi friends.
i have a question about atmosphere and colors, i want to create a sky like the attached image but it affect everything. for example my coloud are red now.
in my file i set the bluesky density to 64 (like wiki terragen samples). the sky will be perfect but when add a cloud layer result will be wrong.

Offline AP

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Re: bluesky
« Reply #1 on: November 22, 2015, 10:26:58 AM »
See if this helps.

Offline majidkaviani

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Re: bluesky
« Reply #2 on: November 22, 2015, 10:43:03 AM »
thank you it`s helpful. but if you add a cloud node you don`t see these colors on clouds :(
cloud colors are orange or yellow .
i have to change color of clouds manually.
anyway its perfect. thanks :)
« Last Edit: November 22, 2015, 12:08:03 PM by majidkaviani »

Offline AP

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Re: bluesky
« Reply #3 on: November 22, 2015, 11:05:59 AM »
Your welcome. I ran into the same issue with the clouds. Hopefully you can solve that part. If not, i will see what i can do to solve it.

Offline Oshyan

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Re: bluesky
« Reply #4 on: November 22, 2015, 07:06:45 PM »
The best way to achieve your result is to think about what is happening in your reference photo - what time of day it was taken at, what angle (toward or away from the sun), how high the clouds might be, etc.

In your specific case I would guess it is either dusk or dawn, before the sun has risen or after it has set. And there is actually very little color on the clouds. So the first thing I tried is just setting the sun to -5 Elevation. That makes it quite dark, but in fact your photo reference probably shows an image with a longer exposure to increase the brightness, so I adjust the exposure in Terragen to compensate. That got me pretty close to the basic look.

Then I adjusted haze amount (increased to 2), Bluesky Horizon Colour (slightly more purple and a little more saturation), and then Redsky Decar Colour (just trying to match what is seen in the reference photo). I didn't nail it, but this is just a quick attempt to get a similar look.

Finally I added some clouds to roughly mimic the basic composition and look in the reference image, but certainly the clouds could be brought a lot closer to the photo with some more tweaking.

Attached are the resulting image and a TGD.

Again the lesson here is that Terragen is generally set up to give you output that matches the real-world for similar conditions. So if you can guess how, when, and where a reference photo was taken (or better yet you took it yourself so you know all those details), it will help a lot in duplicating the look. Yes, you can use extreme settings like 64 Bluesky Density, but this is really not a good way to get a real-world result because it's a very high value and will not respond in expected, realistic ways.

One thing I see a *lot* in reference photos is that the exposure, focal length, and post processing are totally unknown to the person trying to emulate them, and without this information it's very hard to know how and where to start. You need to make educated guesses and get good at analyzing images. Often the colors have been adjusted (I would not be surprised if that is the case in your reference for example), or the shadows lifted, or it is taken with a wide angle lens or telephoto, or even a long exposure in near-total darkness that looks like daylight, and people don't think to try to emulate the same approach in TG. But that is exactly what you want to try to do in most cases.

Take a look at this image for example: http://www.steves-digicams.com/knowledge-center/kcenter/exposure2.jpg
That's a long-exposure, which you can primarily discern from the smoothness of the water. In reality that dock in the foreground was probably actually quite dark to the photographer's eyes, but with a long exposure you gather more light on that foreground object while also smoothing out the water and getting some blurring and apparent motion in the clouds (plus more color and light in the sky). In Terragen there is no "exposure time" (though there is a "blur length", which only works for *camera* motion), so you don't get blurring of e.g. water and other moving elements, but the exposure *brightness* effect works exactly the same way and should be used as such. I doubt most people even use exposure, it's overlooked! But very important just as in the real world.

- Oshyan
« Last Edit: November 22, 2015, 07:23:25 PM by Oshyan »

Offline AP

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Re: bluesky
« Reply #5 on: November 22, 2015, 08:17:28 PM »
Quite an explanation but always good to refresh the mind with these subjects. More or less that seems similar to what i was thinking in terms of what the details in the photograph itself entails. I was continuously adjusting the settings, not with too much success though. I never thought of lowering the sun slightly below the horizon.

Offline majidkaviani

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Re: bluesky
« Reply #6 on: November 23, 2015, 04:53:46 AM »
thank you so much dear Oshyan.
i read your comment Carefully, it was great.
actually i`m working on physical rendering engines for 7 years for creating perfect architectural visual. correct position of lights and using exposure is unaware for me even in terragen, but i think the problem is that i don`t know some of atmosphere options in terragen Scientifically. and i have to test them to understand..
anyway thanks again dear :)

Offline Oshyan

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Re: bluesky
« Reply #7 on: November 23, 2015, 05:57:19 AM »
The Atmosphere controls in Terragen aren't strictly correlated to atmospheric phenomena (e.g. you do not directly control Rayleigh Scattering behavior or anything), but the way that the atmosphere behaves and renders *is* generally quite realistic. You can also achieve very unrealistic results with unusual or extreme settings though. Keep in mind that the defaults are intended to represent "Earth-like normal realism". In the case of the Atmosphere Shader, the sliders have a lot of range in them, but realistic values would really only be within probably 1.0 or at most 2.0 of the default, in other words Haze Density from 0 to 2 or 3 (Default is 1), or Bluesky density from 0.5 to 4.5, at most. Even some of those are extreme values (like Haze of 0, Bluesky of 4.5), so my advice with the atmosphere would be to adjust settings slowly and carefully. Small changes can have big effects, especially with the interdependent Bluesky and Redsky Decay values and colors.

Also note that the values shown in the example images in the Wiki are for illustration purposes, they are not necessarily intended as "recommended" values. I do see in the example for Bluesky of 64 that it gives you a look similar to what you were hoping for, but the important point there is that the sun is in view and even if it may look superficially like your goal, it is such an extreme value that it will ultimately not be an easier or flexible way to achieve a realistic result.

- Oshyan

Offline bobbystahr

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Re: bluesky
« Reply #8 on: November 24, 2015, 06:10:34 AM »
Great thread, thanks Oshyan,,,nice refresher/reminder...baby steps....
something borrowed,
something Blue.
Ring out the Old.
Bring in the New

bobbystahr

Offline bobbystahr

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Re: bluesky
« Reply #9 on: November 24, 2017, 01:42:06 PM »
thank you so much dear Oshyan.
i read your comment Carefully, it was great.
actually i`m working on physical rendering engines for 7 years for creating perfect architectural visual. correct position of lights and using exposure is unaware for me even in terragen, but i think the problem is that i don`t know some of atmosphere options in terragen Scientifically. and i have to test them to understand..
anyway thanks again dear :)

nice work on you web page...
something borrowed,
something Blue.
Ring out the Old.
Bring in the New

bobbystahr

 

anything