AECbytes Tips and Tricks Issue
#21 (August 22, 2007)
Compositing 3ds Max 9 Renderings in Photoshop
Book & Video Author
is the art of creating a new image by combining
images from different sources. In this project,
I will be rendering multiple lighting components
from a 3D model in Autodesk 3ds Max 9 and combining
the results in a new image using Adobe Photoshop
The technique presented here is one possible
solution for overcoming what is a problem with
all high-end 3D packagesexcessive rendering
times for generating acceptable presentation imagery.
I'm not saying that 3D compositing will yield
higher quality imagery than what is currently
possible using 3ds Max, Maya, Softimage|XSI, (or
similar) and a sophisticated renderer such as
mental ray. Instead, 3D compositing is a quick
process for achieving an improved level of realism
from relatively simple, quickly rendered image
There is no getting around the need for a well-built
3D model. Here I have opened a 3D model of the
House in 3ds Max 9. I created a camera,
set the target render size, turned
on safe frames, and composed
the scene. There is one direct light in the scene
and all the 3D surfaces have materials, many with
texture maps and mapping coordinates. You can
download the sample files here
Next on the agenda is to have 3ds Max render
specific components of the total lighting solution.
In addition to the regular Scanline
rendering, we want Diffuse, Shadow,
Z Depth, and Specular
components rendered out to files. These are called
render elements in 3ds Max parlance;
they are added on a tab of the same name in the
Render Scene dialog box.
The Z Depth render element deserves
special mention because it has its own rollout
at the bottom of the Render Scene
dialog. You must enter Z Min
and Z Max distances in that rollout
to get a usable rendering of this element. I suggest
using a Tape helper to measure
the distance from the camera to the front and
back sides of the building. These distances are
approximately 85' and 235' in this project. Z
Depth represents distance in grayscale
as measured along the axis that goes directly
into the picture plane. It useful for simulating
fog and depth-of-field in Photoshop.
Render all elements and save them as separate
.TIF files on disk. Render and save the scanline
image as well (this is what you see by default
in the Rendered Frame window).
The sample file is set up to do all this automatically
when you render.
Another very helpful component is called ambient
occlusion (called clay rendering
or dirt map in some renderers), and it
requires a bit more setup to render out to a file.
Ambient occlusion is not classified as a render
element per se, but is rendered separately by
the mental ray renderer. The interesting thing
about ambient occlusion is that it can give you
very attractive, soft shadows in any compositing
project. Ambient occlusion is calculated from
the ambient light in the scene, independent of
any specific light source.
In a nutshell, to generate an ambient occlusion
rendering in 3ds Max or VIZ, use the following
steps. Open the Render Scene
dialog and open the Assign Renderer
rollout at the bottom of the Common
tab. Set the Production Renderer to
Next, open the Material Editor
and create a new mental ray material.
Assign the Ambient/Reflective Occlusion
map to the Surface component
of the material. Open the Render Scene
dialog alongside the Material Editor
and switch to its Processing
tab. Enable the Material
Override feature and drag the material
you just created from the Material Editor
into the Material Override slot
in the Render Scene dialog box.
Do a test rendering and watch as the mental
ray buckets appear in the Rendered
Frame window. If the rendering is coming
in with coarse grain, hit Esc
to stop the rendering. Go back to the Render
Scene dialog and switch to the Renderer
tab. Improve the sampling quality by
increasing Samples per Pixel
(both Min and Max)
and by decreasing the Spatial Contrast
values. Render again and it will take longer but
the grain will be fine. Save the ambient occlusion
image and close 3ds Max.
Shown below are all the separate image components
which we will now composite in Photoshop.
Launch Photoshop and choose File
> Scripts > Load
Files into Stack, if you are using CS3
Extended. Select the component files you rendered
in 3ds Max and click OK to stack the images as
layers in one document. Do not use the
create smart object option in
the script. If you're using another version of
Photoshop, open all images and drag each image
with the Move tool, one at a
time into one document. Hold down the Shift
key while moving layers between documents to keep
the layers aligned.
You'll notice that the Shadow
layer is completely black. It is a special render
element and must be composited manually. Delete
the Shadow layer and open Shadow.tif
in its own window. Switch to the Channels
dock and observe that it has an Alpha
1 channel that actually reveals the shadows.
This channel must be converted into a layer in
order to composite it into the larger project.
Select the Alpha 1 channel, then
the Select All command, and Copy
to the clipboard.
Switch back to the Layers dock
and create a new layer. Paste
the selection from the clipboard. The shadows
appear white on a black background. Invert
the image by pressing Ctrl+I (Mac: Command+I).
Now the shadows are more properly black on a white
background. Press V (Move
tool), hold down Shift, and drag
this layer into your project document. Rename
the layer Shadow.
The Z Depth layer has the opposite
problem as compared to the Shadow
layer. In order to use Z Depth as a depth map
for the Lens Blur filter, it
must be a channel instead of a layer. Target the
Z Depth layer, Select All, and
Copy to the clipboard. Switch
to the Channels dock, create
a New channel, and
Paste from the clipboard. Switch
back to the Layers dock and Delete
the Z Depth layer.
Compositing is really more of an art than a science.
Photoshop compositing involves playing with blend
modes, layer opacities, layer order, layer masks,
adjustment layers and clipping masksall
the while evaluating the composite with an aesthetic
eye. Once you get up to speed with Photoshop,
these skills will be second nature. The following
image shows what I ended up with in the Layers
and Channels docks.
Probably the best way to understand the Photoshop
side of this technique is to open the sample
PSD file and investigate it yourself. Toggle
layers and masks on and off and kick the tires.
Let me give you a few pointers to help you understand
my workflow. I started by creating a Gradient
Fill layer at the bottom of the Layer
stack. I customized the gradient to blend turf
into sky in the distance.
Notice that many of the layers have masksmost
of these are identical to the Alpha 1 channel.
Ctrl-click the Alpha 1 channel
to load it as a selection. Switch back to the
Layers dock and create a Mask
and there you have it.
While I was compositing, I found that some of
the layers were too dark. I compensated by adding
Exposure adjustment layers and
taking the exposure up a few notches. Be warned,
however, that adjustment layers affect everything
below them in the Layer stackand
that's usually not what you want when compositing.
To make an adjustment layer affect only the layer
below it, create a Clipping Mask.
This is done simply by Alt-clicking (Mac: Option-clicking)
the border between the adjustment layer and the
layer below it. I color-coded layers with their
adjustments, so you can see at-a-glace what goes
The Shadow layer's blend mode
is set to Multiply and the Specular
layer's blend mode is Screen.
I found that the Scanline layer
looked best with Lighten as its
blend mode. Notice that the Shadow
layer is a smart object with Gaussian
Blur assigned as a re-editable smart
filter (new in CS3). I blurred the Shadow
layer to soften its hard-edged raytraced shadows.
The Ambient Occlusion layer's
blend mode is set to Multiply
because it is a type of shadow layer. I custom-painted
a mask to hide portions of the Ambient
Occlusion layer's contribution to the
overall composite. I thought the area under the
second floor deck was too dark, so I masked out
its ambient occlusion by painting in black with
a large soft brush.
The top and final layer started out as a Stamp
of all visible layers. This should be done only
after you are satisfied with how all visible layers
appear by pressing Alt+Shift+Ctrl+E (Mac: Option+Shift+Command+E).
Then I fired up the Lens Blur
filter and selected the Z Depth
channel as its Depth Map. The
lens blur is then applied to objects in the distance
first, fading into sharpness as the Z
Depth channel gets lighter.
Anyway, there should be a lot here to chew on.
Once properly digested (read practiced), these
techniques can really be applied quickly to just
about any project. I hope you'll agree that the
image below is more than the sum of its parts.
In my opinion, it is much more realistic than
what the regular Scanline rendering
in 3ds Max offers, and it took me much longer
to write this article than to render and composite
the entire project using 3ds Max and Photoshop.
A video showing this technique is available
on my free video podcast, The
About the Author
Scott Onstott is a book and video author of
AEC software tutorials. He has a degree in architecture
from UC Berkeley and has served as an instructor
there, in addition to working in several prominent
engineering, architecture, and interiors firms
in San Francisco. He has also worked as a technical
editor and technology consultant.
Scott has contributed to over two dozen books
and videos on AutoCAD, Architectural Desktop,
VIZ Render, Revit, 3ds Max, VIZ, Photoshop, Illustrator,
Painter, Fireworks, and Dreamweaver. He most recently
with Lynn Allen. He can be reached via: www.ScottOnstott.com.
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