View Full Version : Putting images together

06-21-2009, 09:26 PM
I am trying to composite this car into the scene. The problem is, I cant get the front map to disapear. No matter how much I tweak the settings.

I tried rendering the car and shadow seperatly and putting them together in another scene. Using the textured filter under add image filter, in the image processing tab. Although the front map is gone, the render does not look right. There is no occlusion shadows and the car is more blurry.(why doesnt the alpha channel see the occlusion shadows?) Compared to if I render the car with the front map.

The car looks alot better in my opinion if I dont use seperate passes for the car and the shadow. Although, the front map is obviously there if I dont.

I simply want to have shadows without seeing the front map. I have a zip folder with all of the things if someone wants to take a look at it. Just ignore the textures if it ask you where they are.

06-21-2009, 10:39 PM
What do you mean by "front map"? Front projection map? If so, what is it that's using it, because this type of effect doesn't really need one, so it's a bit confusing. ( Can't open your scene just yet, rendering something )

06-22-2009, 01:09 AM
The plane that is receiving the shadow is a front projection map

06-22-2009, 01:31 AM
Oh ok, that won't work. You have to give the plane 100% luminosity and 0% diffuse if you want the photo to look the same as original, and it won't recieve shadows that way. If you have any diffuse to catch shadows with, that will render shading over the image and alter the photograph.

What you need to do is render the car and car shadow separate from each other, and composite them together with the background plate.

06-22-2009, 04:42 AM
You can do this in lw if you don't have a compositing app, what you need are 3 texture layers in the color channel of a polygon, like your front projection. The top layer should have the car render, with an alpha, the middle is the shadow pass, and the bottom is the photograph. Set the shadow layer to Multiply. Put Diffuse at 0 and luminance at 100 and render.

06-22-2009, 01:33 PM
Do you mean put these images together?

06-22-2009, 02:04 PM
Yes, but ideally the shadow pass shouldn't be cut out by the car.

06-22-2009, 11:16 PM
Yes, but ideally the shadow pass shouldn't be cut out by the car.

The car has to be there to cast the shadow though. Right?

06-22-2009, 11:43 PM
Check 'unseen by camera' in the car's object properties.

06-23-2009, 11:29 AM
I got the car to disapear for the shadow pass. Although when I put the images together, it still doesnt look right.

What I'm looking for are the soft shadows around the tires, and the bottom of the car. When I put the shadow and car together from diffrent renders, the shadow only has one value. There are no occlusion shadows.

06-23-2009, 12:15 PM
You should be able to make the shadow pass look just like it did before, in this case it might be easiest to change the shadow color in the light's properties to grey (or ideally to match the shadows in the photo, there's probably a slight tint; usually blue). So the shadow becomes lighter and you can see the occlusion.

Also for compositing you want to render the car on black.

And well done figuring out that you need this type of dual shadow, a lot of people don't realize it. If you look at earlier movies like Shrek, or Monsters Inc., they didn't even bother with it. Always bugged me.

06-23-2009, 06:33 PM
When I change the color of the shadow in the light properties, it does not seem to change what the shadow in the alpha channel looks like. Even when I set the shadow to white, it doesnt look any diffrent then when it is black or grey.

06-23-2009, 07:33 PM
Oh I thought you were rendering the shadow on white -
Just fade the opacity of the shadow layer. But if you use the alpha instead of rendering it on white, you'll have to do the occlusion part as another layer.

Mr Rid
06-24-2009, 03:36 AM
Well, you can not save radiosity shadows separately. :D Only the shadows from lights will show up in a surface set to 'shadow density.' There is probably a workaround.

You have too many lights. Consider outdoor reality. There is only the sun, and radiosity bounce from everything else. So thats all you should have for illumination.

Your key light (110%) should be an area light for realistic shadows, and scaled to roughly the diameter of the sun.

Then GI at 50% will balance out with the key to make the 100% dif ground nearly match the brightness of the BG image.

Spec light flares are fine for tricking birght spec hits, but here they dont really need 'dissolve with distance' values since this is not an animation, and it will kinda compete with the intensity value. It is easier to just enter a single intensity value.

Ray recursion only needs to be 2 for reflections.

Incidence angles in LW are backward. So in LW, '0' is the surface angled away from camera, and '90' is the surface facing perpendicular to camera. Therefore the '0' surface should be more diffuse and more reflective than '90.' Your dif incidence was backward thus creating a dark edge.

Dif and reflect values should not total more than 100% at a given angle. So if your dif is 75% at '0' then the reflect can not be more than 25% at '0'. Otherwise the surface will become unrealistically luminous looking.

You had an image in the reflect texture that should not be there. The image texture will only use the grey values of the image to determine how reflective the surface is. I think you wanted to have the image reflect as an environment which would go in the environment tab- reflection options- spherical. You have more control to map images on geometry like an enviro sphere to get reflections and ambient GI rather than using textured enviro.

Should not have a luminous value on the wheels.

Tires are too bright.

I also like to make most texture images 256 color png so they take up a third as much ram in the scene.

So you get something like this-

06-24-2009, 11:05 AM
The shadow catcher is still visable in your render though. How do you get rid of it?

Mr Rid
06-24-2009, 11:35 AM
You cant easily get rid of it in your LW render. Lightwave is not really a compositing tool although there are tricks/workarounds for it. You could put a transparency grad around the edge of the ground to fade/blend it into the BG but that is a bit crude, or you can fudge it in 2D. You really have to render separate elements and composite them together as Toby is saying, although there is no way to isolate the radiosity shadow I can think of. Compositing is best handled in an app like After Effects, Fusion, etc. I have always wanted a way to have an object only render as a shadow within the scene, like you want. I see on Flay there was a plugin called TransShadow that may have worked but does not appear to exist anymore.

06-24-2009, 02:08 PM
I thought it was an ambient occlusion shadow, guess I should've opened the scene -
Regardless, if the ground is all white except for the shadow, it should all be taken care of by the fact that you're multiplying it over the background. Multiplying white (1.0) over any color (background photo) equals that same color. So the only thing you'll see is the shadow.

06-24-2009, 03:19 PM
I have adobe after effects cs4. How can I use it to my advantage for this?

06-24-2009, 04:03 PM
Here I've set it up the way I do radiosity shadow passes. Couple things to look out for:

The value of the ground outside the shadow is above 1.0, so if you save a floating point image it will give you bad results in a comp. Saving it to a 24 bit image will clamp it at 1 (no alpha for this pass). If it's below 1 it will darken you background, above 1 will brighten it, so you need it exactly at 1.

There is color in the non-ambient part of the shadow, because I use the same background to render the shadow pass to keep the brightness of the shadow more accurate. In most cases you'll want to completely desaturate the render before comping it.

And I see you do a lot of cars; what's REALLY important for the car's paint is a fresnel curve in the reflection, set to around 1.5 - 1.7.
1.52 is accurate for glass, but sometimes you want a little more shine.

Mr. Rid is right about not using a distant light, but the DP Infinite light is more convenient than an area light; acts like a distant light, but you can tell it how soft you want the shadows, the sun is 2 on a clear day. Highly recommend the DP light plugin.

Also I noticed that the windows are whacked when using the perspective camera - that's usually because polygons are badly non-planar. The classic camera is very forgiving, but it's still better to fix the polygons.

06-24-2009, 04:09 PM
I have adobe after effects cs4. How can I use it to my advantage for this?
Sweet! Set up a comp the same way as :

top layer should have the car render, with an alpha, the middle is the shadow pass, and the bottom is the photograph. Set the shadow layer to Multiply (blend mode).

Mr Rid
06-24-2009, 05:43 PM
...the DP Infinite light is more convenient than an area light; acts like a distant light, but you can tell it how soft you want the shadows, the sun is 2 on a clear day. Highly recommend the DP light plugin.

Nice. I just scale an area light to control shadow softness.

06-25-2009, 11:27 PM
I am still trying to learn this. Although, thank you guys for so much help.

06-26-2009, 01:47 AM
You're doing good dude, keep at it, let us know if you get stuck

Mr Rid
06-27-2009, 11:18 PM
I tried a rough experiment to isolate trace & GI shadows. Not perfect, but I rendered black light with a white shadow (must be all white geometry) which gives me an inverted shadow pass. This can be used as a luminosity mask to add shadows in comp, or as a front projection map in scene.


The shadow pass might also be rendered with the surface baking camera to be applied as a UV texture in scene but would have to rendered separately for each object receiving shadows.

Floor plane-