Spherical Sky output is very different from source

[shaisamuel]

Hi,

I am using Spherical Sky, with sky high resolution professional sky image I have purchased from Poligon (HdrSkyCloud004). This comes with an HDR file (.exr) and high resolution 6k jpeg file (4.4MB). As I didn't see any option to use the .xpr file, I am using the jpeg file.

HdrSkyCloudy004_JPG_6K.jpg (4.18 MiB) Viewed 11495 times

This is my environment setup:

Screen Shot 2020-09-09 at 5.57.18 PM.png (99.99 KiB) Viewed 11495 times

The results are very disappointing, as if they come from a totally different file (1920x1080, 07. High+)

Y3.png (2.58 MiB) Viewed 11495 times

There 3 issues:
1. The winter like sky & clouds that show on the rendering resoult
2. The overall low quilty of the sky
3. The block horizon area. As far as I know, one way to go around it, is tomove the center line of the background image a few pixel down. I wounder if there is more elegant way around it.

Thank you, Shai

[Fletch]

Hello Shai,

You will need to convert the .exr file to an .hdr in order to use it with Sperical Sky and actually have it "act" the way the .exr would. .exr and .hdr are both high dynamic range image formats, while .jpg is going to "cast some light" onto your scene with Twilight Render, .jpg is a low dynamic range image, and therefore Twilight's engine is trying to do some "clever magic tricks" in the background to try to "fake" the .hdr effect.

So, simply open the .exr file into any appropriate hdr image editor, and save as .hdr. Then try the sky in the spherical sky slot.

The difference between .jpg and .hdr?
Basically - a .jpg image can only contain colors between 0 and 255 (study RGB image colors) while and HDRi can contain a much much higher dynamic range of colors in that same pixel. I do not know the exact values. But it's simply not even a contest.

Twilight Pro allows you to save your renderings in .hdr format or .exr because the render engine actually renders the image in high dynamic range, but compresses this info to be able to display the image on your computer screen in a way that makes sense to our digital screens and eyeballs. You can save as .exr or .hdr and open in any hdr image editor and tweak the exposure inside that program much more dynamically than you could with a .jpg which would lose the info in the darks and lights areas more quickly.

[shaisamuel]

Thank you so much, Fletch, for your quick, and helpful reply.

I followed your advice, converted the file (using the first free link that comes when searching google, as you demonstrated), changed the environment, and ran the rendering. I don't have all the relevant scenes yet, as some of them take 7-10 hours to run, even on that relative strong server I rented (an Intel Xeon E5-2450 2.10 GHz with 2 processors, SSD server, 12GB RAM, that run 32 treads when rendering, for $79.95 monthly. I think it's a great deal, one of a few that offers a solution to RDP limitation of nor running OpenGL. The solution is using NoMachine as a remote desktop, at lease to open the SU file).

As you can see below, there is very small difference between rendering with the 4.4 6K .jpg sky file

Rendered with 6K .jpg file (4.4MB) as sky

G2.png (1.47 MiB) Viewed 11476 times

and the rendering with the new 26.7MB .hdr sky file.

Rendered with 6K .hdr file (26.7MB) as sky

G2.png (1.48 MiB) Viewed 11476 times

[shaisamuel]

Hi Fletch,

I understand now that these large clouds are what we see near the horizon, and in the .jpg they look really small, but when rendering they become really large, and therefore cover the entire sky. Is there a way to control the ration of the image used, for it to use a bigger portion of the sky image?

As far as the dark area below the horizon, that is the SU ground which is not covered with material. Is there a way to setup the color or material of it? In SU it is defined in the Style, and with the Sky background it should be the ground image below the horizon, but of course, none of the images I found fit the topography of my area. Any advice?

[Fletch]

A test I suggest is to hide everything in your scene and put a cube or ball painted 50% grey, next to a white (70%) and dark grey ball (10%) on a basic 50% grey field the same size as the field you are trying to render in the full rendering.
Use the same sky settings, but switch the sky for .jpg or .hdr and save the two renderings and compare.

It would be surprising to me if your image results were the same. That said, you are rendering a scene which is notoriously difficult in visualizations - that is a drone-type view of a very large area - it would be very difficult to make it realistic without a lot of effort to model everything correctly, and have very good and properly mapped materials. A low res projection of an unrealistic looking ground will never look good in any render engine.

So you have set up a nice challenge for yourself here, I would be hard-pressed to create a photo-realistic image of this scene. I find birds-eye/drone-eye views very difficult. Proper 3D vegetation models would also be very important, where applicable.

There 3 issues: You hav
1. The winter like sky & clouds that show on the rendering resoult
2. The overall low quilty of the sky
3. The block horizon area. As far as I know, one way to go around it, is tomove the center line of the background image a few pixel down. I wounder if there is more elegant way around it.

Thank you, Shai

Just because an image is a "professional image" doesn't make it perfect for your needs. It may be a good photo. This doesn't make it good for your situation. It may be, it may not be. You have purchased a hemi-spherical sky, not a spherical sky. A spherical sky should also have the ground.

regarding question 3 above, you could use a photo editor and mirror the sky so that when it hit the horizon it "melts" down into more sky, so that your model's horizon line would be the only one.

Subject: Sharper background

You will need to create or buy higher resolution spherical skies.

The portion of sky visible in your camera view needs to be similar in the number of pixels compared to your rendering.

For example, if the spherical sky used in your image here is 4000x8000 pixels, and your camera captures 1/8 of the sky image, then it will be capturing 1/8 x 8000 = 1000px wide. So if your final rendering is 2000px wide, it will stretch the 1000px to be 2000px wide, resulting in a blurry image.

Easiest answer is to use Alpha Mask to insert a high resolution background image in post-processing.
Subject: How to use the Alpha Mask / Alpha Channel
So why use the spherical sky image? It helps to give nice reflections, and if you match your new high resolution background to be same general brightness of the spherical sky, then the results will be quite realistic.

[shaisamuel]

Thank you Fletch for your patient and passionate detailed replies.

I am learning a lot. Yes, this is a huge challenge, and it is real for me, as this model is of a project I am working on, and trying to make its visualization as attractive and real as possible. My budget is kind of limited, and so I need to struggle with it myself. The model as I mentioned is huge (25 million edges, 10 million faces, 650 component definitions, that creates 450,000 components, file size 170MB). I am applying metrials and editing them, but on my computer (An older mac book pro that gives 4 treads) it's quite a task, so I can only do prelim, and process is daunting slow. I am running the rendering on a stronger server which results in 32 treads, but each of my realistic improvements make the rendering take longer (10-20 hours per scene, with 40 scenes).

I understand these drone like view are a big challenge, but they are the ones that give the nice view on the model area. The sky with clouds give it a soft and more realistic touch.

Ground
1. I have tried to download as much detailed images as possible of the ground from google earth pro. I believe I got the maximum resolution available in this area. I am trying to add some bump to the sendy area which is close to turn the dark bushes in the image to show some depth. I used simple Sketchup bump of 1. Any suggestions?

2. I do have vegetation, mostly palm trees, which is the plan. They are placed with random size and rotation. Do you think they can be improved? I guess I need to add some stones on the land, which is what we have in life. I could use the same randomize extension to scatter stones all around, but I am afraid to turn the long rendering to be extremely slow. Any idea how to do it, without turning the rendering to be much slower?

Skies
3. The reason I have chosen to use a hemispherical sky, and not a spherical sky, is I couldn't find one with clean horizon. Anything else, bring objects (trees, houses, powerline) that are not proportional to the distance they should be, as my area is large and flat (desert). This hemispherical has clean horizon. I like your idea of mirroring (I tested cropping the bottom, which works, but it's hard to anticipate the size on different scenes). Is there a way to do this on the .hdr or just the .jpg?

[Fletch]

The model as I mentioned is huge (25 million edges, 10 million faces, 650 component definitions, that creates 450,000 components, file size 170MB).

This is not really that big for a 3D model, although for SketchUp it is perhaps "big", a good modern computer could handle it. For working on this type of scene on a regular basis I would suggest a much stronger machine. 32Gb RAM (min), high speed SSD drives, much better processor (16 core min), much better graphics card, etc. etc.
You should still be able to work on it, but you will need to be smart. Be sure to put objects on layers - control which layers are on and off via your Scenes, so that you can quickly switch "working modes" like vegetation, or buildings, etc. Obviously turn off all the edge junk so that you only have normal edges, no profiles, no endpoints, etc. Disable the automated animation movement of the camera so that every time you click a scene it will not try to animate the movement, but just jump to the scene you choose - this will save 2 seconds every time you click a scene, which adds up to a lot of time over the work day.

I am applying metrials and editing them, but on my computer (An older mac book pro that gives 4 treads) it's quite a task, so I can only do prelim, and process is daunting slow. I am running the rendering on a stronger server which results in 32 treads, but each of my realistic improvements make the rendering take longer (10-20 hours per scene, with 40 scenes).

As a beginner with a weak machine you have thrown yourself into the deep end of the pool. I highly suggest a good workstation. But if you work smart, and do very small previews and work judiciously you may be ok.

I understand these drone like view are a big challenge, but they are the ones that give the nice view on the model area. The sky with clouds give it a soft and more realistic touch.

Ground
1. I have tried to download as much detailed images as possible of the ground from google earth pro. I believe I got the maximum resolution available in this area. I am trying to add some bump to the sendy area which is close to turn the dark bushes in the image to show some depth. I used simple Sketchup bump of 1. Any suggestions?

A seamless high quality appropriate desert sand texture combined with a perlin noise to modify the looks of the instances would be better. If I was working on that project I would probably export my scene to Twinmotion/Unreal engine because they have procedural skies and lots of plants/vegetation and a full endless desert environment and you can bring in your SketchUp scene. It renders on GPU (requires a very good GPU computer, not your Mac, sorry) so it's much faster. Still requires a much higher end computer than what you are using.

2. I do have vegetation, mostly palm trees, which is the plan. They are placed with random size and rotation. Do you think they can be improved? I guess I need to add some stones on the land, which is what we have in life. I could use the same randomize extension to scatter stones all around, but I am afraid to turn the long rendering to be extremely slow. Any idea how to do it, without turning the rendering to be much slower?

Use Twilight Instances - this allows you to select any component - right-click and choose Twilight V2> Proxy Tool and you can just click around placing the instances around your scene, then use the random scale rotate tool on those proxies. They will render the full geometry, but only show a wireframe box in SketchUp. This keeps memory usage low, and speeds renderings. For Grass, Bushes, Trees, Stones - try Skatter plugin - works with SketchUp and Twilight Render.
Twilight Render Proxy Objects
Subject: Twilight V2 and Skatter

Skies
3. The reason I have chosen to use a hemispherical sky, and not a spherical sky, is I couldn't find one with clean horizon. Anything else, bring objects (trees, houses, powerline) that are not proportional to the distance they should be, as my area is large and flat (desert). This hemispherical has clean horizon. I like your idea of mirroring (I tested cropping the bottom, which works, but it's hard to anticipate the size on different scenes). Is there a way to do this on the .hdr or just the .jpg?

Any image editors that can open and work with EXR or HDRI should be able to allow you to do just this.

[shaisamuel]

Thank you Fletch, for your great advice (as always).
I looked at Twinmotion, and it is an amazing solution for me. My computer is too weak for it, but my server is OK. I am studying it, and getting progress. It will not only allow me to manage a large project faster but will also allow me to easily create very rich animations.

[Fletch]

It is as if you are trying to fit an entire dump truck's load into the back of a small Toyota pickup.