End date: May 13
User avatar
By Ernesto
#366071
Hello,

Spanish Competition Deadline on April 29, 2013
I have just saw the anounce, http://www.maxwellrender.com/ and wondered which is the best way to achieve reflections and shadows on the ground shown in the HDR image. http://www.maxwellrender.com/gallery/ma ... ompetition

1) Light Source:
I tried the HDR images as background and as lighting sources, this will guarantee the lighting consistency between the rendered object and the background or the ambience.

2) Shadows on the Ground:
I assume (but never tried) that we should use a shadow channel to achieve the shadows on the floor. Previously it is necesary to match the sun angle / position to the sun in the image.

3) Reflections on the Ground:
I really have no idea how to make an object to be reflected in the floor that is shown in the HDR image.

4) Reflections on the ground stored in the HDRI vs reflections Produced by the model:
I assume there will be a conflict, between both reflections, that should be solved.
My main concern is that all the scenes are backlighted,
Image
so we can see (in the images) reflections in the ground, which should or not, be blocked partially deppending on the object that will be rendered in the scene, but that seems to be impossible since the reflections are stored in the HDR image. Additionally if the model contains lightsources, they would have to produce new reflections, which should be consistent with the material caracteristics represented in the HDR images. That seems to be the main challenge...

Thanks in advance!

Ernesto
User avatar
By Ernesto
#366314
I was told that in certain softwares it is possible to project the HDRImage on a ground plane, so that this ground plane will render invisible, but the objects would project shadows on it, as well as reflections.
I wonder if this is possible in Studio or Maya.

Ernesto
User avatar
By sinmania
#366317
Hey Ernesto try this....

for mental ray the guy sais here
"5) create a plane for your ground and assign the Use Background shader to the plane.
6) select the plane and in the attribute editor go to the useBackground 1 tab and set the Specular color all the way left to make it black and reflectivity and reflection limit to 0"
Other option
Try this on the plane maybe it works to hide the plane visibility: maya help

Good Luck!
User avatar
By Ernesto
#366423
sinmania wrote:Hey Ernesto try this....

for mental ray the guy sais here
"5) create a plane for your ground and assign the Use Background shader to the plane.
6) select the plane and in the attribute editor go to the useBackground 1 tab and set the Specular color all the way left to make it black and reflectivity and reflection limit to 0"
Other option
Try this on the plane maybe it works to hide the plane visibility: maya help

Good Luck!

Thank you!!
I will try

E
User avatar
By dariolanza
#366425
Hi Ernesto,

Yes, you will have to maintain the ground object as visible, but apply regular diffuse material textured with the footage picture in camera projection (you will have to set the camera projection in Maya). This way it stays visible, while it receives light and shadows from the scene, like a regular textured object.

Enabling the Shadow option (and enabling the Shadow Channel) you will get the shadows being cast over the ground, which can be useful for compositing purposes.

Here you can read more about exporting the Shadow channel:

http://support.nextlimit.com/display/ma ... ow+channel

Greetings

Dario Lanza
User avatar
By Ernesto
#366431
dariolanza wrote:Hi Ernesto,
Yes, you will have to maintain the ground object as visible, but apply regular diffuse material textured with the footage picture in camera projection (you will have to set the camera projection in Maya). This way it stays visible, while it receives light and shadows from the scene, like a regular textured object.
Enabling the Shadow option (and enabling the Shadow Channel) you will get the shadows being cast over the ground, which can be useful for compositing purposes.
Here you can read more about exporting the Shadow channel:
http://support.nextlimit.com/display/ma ... ow+channel
Greetings
Dario Lanza
Thanks Dario,

I did manage to set the UV of the ground plane for camera projection.
I created a new difuse material using the background image, I tried using the spherical full map, and also the cropped map provided for the competition, and I could render an image where the object cast shadows on the ground.
However I must be doing something wrong... because the image in the ground plane do not match the background image.

Image

Any Idea on what could be my mistake?
thanks again

Ernesto
#366440
Hola Ernetsto, como estas?
Lo que tienes que hacer es como lo menciona Dario, crear el plano y encender la opcion "shadows" tanto en el material de tu plano, como en los canales de salida del render y en las opciones de tu plano en 3d, tendras que apagar la opcion para que no sea visible en el render, de esta manera en tu render no aparecera el plano, pero en tu canal shadows estaran todas las sobras sobre el mismo. Mientras esta el proceso del render, tu no veras las sombras reflejadas en el plano, esto es porque las sombras estan en un canal aparte, ya las tendras que poner por separado en el proceso de postproduccion de tu imagen...

espero que te sirva y cualqueir duda por aca estamos
saludos
User avatar
By Ernesto
#366459
Dario, Fernando

Thanks: Finnally I have got the way to have a shadows channel and a rendered image with the object supperimpossed.
This is not what I was expecting, but could be a way to do it.

Perhaps I was trying to do something that is not possible.
I was expecting to render an image where there would not be a need of posprocessing.
I wonder if this is possible or not. It seems my expectations were wrong...

It seems that all the documentation on ther subject, explains a way to render diferent channels which would need to be composed into a final image using an image post processing software.
As here: http://hdri-spherical.com/tutorial-usin ... art-2.html
I wonder if this is the only way to do it.

Finnally, which is the recomended way to use the shadow channel to create the shadow in the rendered image?

Thanks again.

Ernesto
User avatar
By Ernesto
#366520
Finnally this is what i have got:
Image

I am not really happy with it, and it could be because i am just guessing the procedure.
If someone have a better method, I will be more than happy to know it!
Here is what I did:

Placed the 3d model.
Used the HDRI as image based lighting, as well as background and reflections.
Created a ground plane.
Assigned a gray material with the checked boxs: Mate and Shadows
In Rendering settings enabled a shadows channel.
It rendered the 3d model against the HDRI background but the ground plane and shadows were invisible.
Then posprocessed in Photoshop as follows:
Started with the rendered image, then created an empty alpha channel, and pasted into it, the shadows channel rendered in maxwell. Then used it as a selection, which edited with the comand EXPOSURE, and darkened it a but to produde the shadows effect.
What i do not like is the white line in between the 3d object and the background, and that the shadow looks unrealistic, since you can see that there is a reflection on the ground (in the HDRI) that was forced darkened, but is still light, and the legs of the flying machine looks like they are not producing real shadows.

It looks to me not realistic, but I cannot tell the reason.

One thing I liked is that the upper wing against the sky, shows difractions similar to the sundisc in the HDRImage. This was done playing arround with the Difraction slider, as well as with the scattering sliders.
I am happy with this effect!


Here I tried combining the rendered image and the shadows channel, in photoshop, using the Multiply mode:
It seems to work better, although the white lines are still there...

Image

Ernesto
User avatar
By Mihai
#366559
It's not a bug, rather a limitation of how antialiasing works. The solution is not to render out knocked out shadow passes on some cases:

http://support.nextlimit.com/display/ma ... ow+channel

see further down that page, "Knocked out shadow pass vs Full shadow pass".
studio on linux

Thank you! Got it running now. I am on Debian Stre[…]

I would like to create a render that shows a backg[…]

Hi everyone~~ Does anyone know how to create the […]

How do I import Houdini Hair into Studio? What ge[…]