Photo input to Clouds

Started by fleetwood, February 02, 2014, 10:01:14 pm

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fleetwood

In response to overwhelming demand by people who have asked me how
this effect was done (2 people) here is Fleetwood's Cheesy Cloud Effect otherwise known as :

                           Using photo input to create a Terragen cloud

Original Example Photo is a public domain image from NOAA.
This effect is likely best suited for still images.

Disclaimer : This effect is kind of like a Trompe L'oeil painting in that it fools the eye. The cloud it produces is a parallax dependent effect that has a degree of sculpted depth which responds to light and shade and absorption so it is more three dimensional than a simple flat backdrop or billboard, but it will not magically create a duplicate of nature. Afaik you cannot produce a fully sculpted model of a real cloud in all dimensions from the information in a single two dimensional photo.


Finding or making a cloud photo for this effect -  A photo that has back light or flat lighting may be easier to deal with.
My theory on this - Because the colors in a photo of a cloud are partially from transmitted light and partly due to reflected light every photo isn't going to serve as a great density map by itself.  In other words a sunny day photo of a big puffy cloud might be bright on the left and dark on the right. This doesn't mean the cloud is denser on the light side or the dark side, it just indicates light intensity and direction. When the light comes through from the back or above a cloud, the colors and shades reveal more clues about density.



1. Make a cloud-mask in an image editior :
  Crop the cloud photo removing the land and extraneous sky.
  Decide whether to Invert the photo - depending on your judgement - if the photo has a lot of dark areas of cloud that you judge to be the very dense areas, then invert the image so that those areas are whitest. Some photos will work without needing to be inverted.
 
  Black out any remaining land and all areas of clear sky and any unwanted clouds. Hand paint and clone areas if desired according to your inclination and editor skills.

2. In Terragen set up a cumulus cloud layer. In this example I'm using a global layer at 600 feet altitude depth of 450 not localized. The greater the depth the more blur in the resulting Terragen cloud in comparison with the photo.  The cloud layer needs to extend to the horizon in this example or else there will be a gap between the low cloud and the ground. The base density input is a regular cloud density shader with its color offset pushed up to 1. This gives a dense cloud layer with slight variation as a starting point. You could use a constant color.

An image shader is created using the cloud-mask I've created. Projection is by a separate camera that is in approximately the same position  as the Render camera but has a little more restricted fov and it can be tilted to move the projected density around if needed.

The cloud-mask image shader can be piped to a colour adjust and then it can be tried in any of the cumulus cloud inputs.
All the cumulus inputs can be experimented with. In my example the negative cloud-mask is plugged into the Final Density only.
I've made a second cloud-mask shader using the positive (non-inverted) version of the cloud-mask. This positive mask is plugged into all of the cumulus cloud light inputs, Direct, Env., and Ambient.

The mode of the cumulus cloud can be set to 2d in the quality settings for tests or final render if that look is preferred. 2d shows more detail from the photo and renders more quickly while 3d volumetric has more depth and appears softer.



yossam

Thank you sir..............off to play.  :)

TheBadger

Thanks a whole lot fleetwood. This is some nice stuff your explaining.
It has been eaten.

Dune

Thanks fleetwood. This is interesting, something to play with again.

bobbystahr

something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist

bobbystahr

Well...here's what I came up with...a fine technique that I recall messing around with a while back but I had a few things wrong which were illustrated by your project. Thanks for the tute. It's a bit low res in the atmosphere samples but at 10 hours for a test I'll not redo this one, but take lessons learned forward with me.
something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist

TheBadger

It has been eaten.

fleetwood

Nice render. Bobby.  Didn't see it until today. Has a pleasing painterly quality.

bobbystahr

Quote from: fleetwood on March 21, 2014, 12:26:44 pm
Nice render. Bobby.  Didn't see it until today. Has a pleasing painterly quality.


Thank you...this is a fine technique that I am having a fair bit of fun with...I have another 2 tests I'll upload later to this thread and message you....Thanks again for the inspiration!
something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist