mental ray beginner question

[zero123abc]

hi friends , currently i'm learning maya mental ray lighting and rendering ....still learning the basics ......

i have a little scene and i tried to render it in maya mental ray ......in this case i used maya physical sky and sun method ....so when it turns on the final gather is also automatically turned on .... i gave a same Lambert material to all of my objects before rendering

http://i40.tinypic.com/1179z13.jpg

so in that above pic the roof is well illuminated ( which should be ) ..... the chimney is located above the roof.....the thing is , the chimney may be illuminated but it visibles in a dark color even having given the same material to all the objects and there shouldn't be any shadow too

the direct light setup image will also help u to recognize the issue


http://i44.tinypic.com/14ccsiu.jpg

so can some one explain why it happens....thanx

[chopmeister]

I'm sorry but I don't see the problem. If you compare the sides of the chimney with the corresponding parallel sides of the house, you will see they are identically lit, which is normal, since the sun is coming from the same angle. I work in Max not Maya but the thing is, on the preview of your scene, the sun is coming from the house towards the snowman, and in the render the shadows fall as if the sun is pointing from somewhere above the camera towards the house, are you sure the render and the scene view have the same setup?

Otherwise as for the render itself, it's perfectly good. There's no mistake, the chimney is supposed to leave a shadow on the roof because it blocks the sun's rays from falling on that part of the roof. Final gather aside, the intensity of the sun is very strong, and so it leaves a dark shadow. The shadow on the house is less dark because there is a lot of light bouncing from the ground.

[zero123abc]

I'm sorry but I don't see the problem. If you compare the sides of the chimney with the corresponding parallel sides of the house, you will see they are identically lit, which is normal, since the sun is coming from the same angle. I work in Max not Maya but the thing is, on the preview of your scene, the sun is coming from the house towards the snowman, and in the render the shadows fall as if the sun is pointing from somewhere above the camera towards the house, are you sure the render and the scene view have the same setup?

Otherwise as for the render itself, it's perfectly good. There's no mistake, the chimney is supposed to leave a shadow on the roof because it blocks the sun's rays from falling on that part of the roof. Final gather aside, the intensity of the sun is very strong, and so it leaves a dark shadow. The shadow on the house is less dark because there is a lot of light bouncing from the ground.

first of all many thanx for ur quick reply mate :)....... yeah actually the scene and the render has the same light setup ..... i only rotated the viewport to show the light direction clearly ( not the light )

yeah the chimney shadow is ok ..... i agree with that ...... but i'm telling about the colors of the roof and the chimney ..... coz the chimney ( not the chimney shadow )should be very lighter and almost same as the roof color...... but it's got a dark color even i've given the same Lambert material to all :(..... thanx

[Russell123]

Hi friends hope all will be fine. Zero i am sending some link via messages check them hope they will provide you some good information about it.
thanks

[2bitfxprod]

yeah the chimney shadow is ok ..... i agree with that ...... but i'm telling about the colors of the roof and the chimney ..... coz the chimney ( not the chimney shadow )should be very lighter and almost same as the roof color...... but it's got a dark color even i've given the same Lambert material to all :(..... thanx

I think what chopmeister is trying to say is that the physics of the light are correct because our perception of color and intensity of light is based on the angle of the light to the reflecting surface to our eye. In this case the roof is "reflecting" more of the light rays back to our eye from the light source giving it the impression of being brighter than the roof. Which it is in the sense that it is sending (reflecting) more of the suns energy to our eye than the surfaces of the chimney.

I think that if you were to try some other light positions you would find you could find the same result only reversed, with the greater light reflected being from the chimney and not the roof (or the walls or some other surface).

Hope this helps. Have fun lighting.

Rob Au
Lighting TD
Rhythm & Hues Studios

[Johnherpes]

this PDF explains how to optimize a mental ray rendering in XSI. its a bit older but nevertheless full of good informations you dont wanna miss ni case you have to render under deadlines.

[richiexu]

i think the lighting is physically right.The color of the chimney and the color of the wall which is prarallel to the chimney are similar