View Full Version : Reflection help needed.

02-13-2009, 04:09 PM
Is there a way to get a solid white surface to reflect an object?

What I do is a lot of "isolated objects" on a white surface (countertop) and I need the surface to be pure white but would still like to see some reflection in it. Many times I can do it in post using Photoshop but would like to know if there is a way to do it directly in Lightwave.

Below is an example of a film strip (in progress) on a surface, now if I make the table top grey I can see the reflection fine (reflection set to 100%). However if the surface is set to white and reflection 100% it fades out almost immediately, basically you see the reflection only where there is a bit of a shadow.

I have the table top set to ray trace + Spherical map.
Luminosity 0
Diffuse 100
Secularity 0
Reflection 100
transparency 0

I had good results a long time ago but can't for the life of me remember how I did it.

Any ideas?

02-14-2009, 09:07 AM
Did you make a separate reflection pass and add it in post? Short of that, I don't see how you could do it with those surface settings. Pure white is that, pure white, so it blows out any reflection that may be there.


02-14-2009, 09:32 AM
ok, to explain, this just extends the possiblities of a forum thread. :D
(You might consider to buy a "Lighting" book or wiki for "additive color mixing").
So, just a few hints:
you can't add color to a pure white (RGB 255 255 255 value), as this is just the end of the tonal range.
Therefore, you will have to achieve a "pure white" look, not a technical pure white.

In general, it seems you have far too much light on that (100% Diff) ground plane and that is overkill for any possible reflection. To make things worse you have additionally 100% Reflection of a pure white backdrop.
Play with surface settings and lighting to achieve the desired effect.
You could start with a "too dark", "greyish" image and get the relation of the tonal range right, then brighten up the scene carefully by changing surface settings and lighting.

In "real world" a reflection on a white surface will always be quite weak (you already noticed by yourself, that it works better on darker surfaces, even when, in your case, that reflection on the grey plane is not photorealistic, as it is brighter than the object itself - this seems to come from a combination of white reflection color in surface plus reflection of white backdrop).

02-14-2009, 02:33 PM

William shows how to do this in the above thread.

edit: opps.. that thread was about shadows on a white bkrnd, not reflections...

02-14-2009, 03:41 PM
I know what I am trying to achieve is not "real world" And I can do it in post but I was hoping that there was a trick to getting the desired effect in Lightwave.

Here is a picture that is basically the effect I am going for

I guess I might have to do it in Photoshop if no one has any idea how this can be achieved directly in Lightwave.

02-14-2009, 03:51 PM
Right after posting the reply above I had an idea on how to achieve the effect in Lightwave and it worked. I knew I had done it almost a year or so ago but forgot how.

I had the reflection options set to "ray trace & spherical map". The solution turned out to be setting this to "Ray tracing & Backdrop" then setting the lights in the scene to exclude the table top surface.

This way it was only effected by reflections and not by lights at all.

Below is a quick render of the results.

02-15-2009, 12:23 AM
Which are the settings for the surface?
Diffusion and luminosity?

Thanks for the info.

Edit: Never mind, Diffusion 0 and a balance between reflection and luminosity.

02-15-2009, 01:00 AM
Luminosity 0
Diffusion 100

That is for the sample above. I actually lowered the reflection to 50% and up'd the luminosity to 40% on the final render to soften the reflection a bit but still keep the table white.

02-15-2009, 01:05 AM
Right, and reflection 100%.

02-15-2009, 08:14 AM
The way I would do it is

- give the tabletop surface a white color
- set the total of diffuse and reflection to 100%
- add a fresnell for reflection fall-off strength
- give it a bit of reflection blurring
- Put the scene in a white sphere (polies inverted)

Diffuse and reflection are basicly the same thing, reflected light. The difference between them is that DIFFUSE scatters the light in all directions (because of surface irregularities) and REFLECTION doesn't. That is why the sum of DIFFUSE and REFLECTION can't be more than 100%, if it was more than 100% there woud be more light being reflected then what is illuminating the object, making the object basicly an illuminating object. Reflected light is OR scattered OR not, if DIFFUSE and REFLECTION values were both 100%, the reflected light would be 100% scatterd (DIFFUSE) AND 100% direct (REFLECTION), impossible in real life, and a 3D aplication would add those light values together, giving 200% light being reflected from the object (scattered and direct).

To make your tabetop white while at the same time having object reflections, it has to reflect white. Your object reflections are blocking the white reflections (well, actualy the object themselves are blocking the white reflections) and thus you'll get exactly what you want.

With the fresnell you can controll the fall-off of the reflection and with the balance between the diffuse and reflection values you control the reflection strength.

(DIFFUSE and REFLECTION in capitals mentioned above mean the LightWave parameters)