Step 2: Using the HDR image to generate lights to create lights
this stage we will be deriving actual Maya lights from the HDRI image
through the use of the exported Lightgen file that was created earlier
Load Brock's Lightgen Control script
This will bring up a panel which allows you to import your lightgen outputted MEL file
Brock's Lightgen Control at load up
From the File Menu choose Lightgen Script Open and open the MEL file you created in Lightgen.
Open the lightgen script
After the script is opened you will now be able to control the directional lights created from the script.
Brock's Lightgen Control after MEL script loaded in
It is also possible to adjust the Light Hue, Saturation, and Value for all the lights.
Shadows may be enabled from the Upper, Lower, or all of the Lights in Dmap or Raytrace
the lights are looking good it is important to break the Intensity so
that each light may be tweaked individualy. Without breaking the
intensity the values are locked to the dimmer
It is also possible to break all the other connections to the lights so that the shadows may be tweaked individually too.
Continue to modify the lights so that they provide good lighting for the model as shown below.
Second step in Maya (left) and the resulting rendered image (right)
Step 3: Creating scene specific elements
some CG mock-ups there may be "special" lighting situations that need
to be created. Examples include caustics and fog. If this step is not
required for your CG mock-up, you may skip this step (pp 57).
The Brock's Lightgen Control script also allows the input of an additional Lightgen MEL file
Generating additional lights
Set the percentage first of what amount of lights to keep then click Generate and browse to the appropriate file.
Once the top percentage of the lights have been selected then enable light specific items for those lights
is an example image of an object that would require special lighting.
On the left is the Maya setup and on the right is the image rendered in
Maya with just a caustic pass.
Third step in Maya (left) and the resulting rendered image (right)
Advanced Use: Matching a specific angle and creating shadows
order to make the final result look as convincing as possible there are
two additional advanced used stages that can help blend a CG mock-up
into the live action photograph.
camera in Maya can have an image plane attached to it. By mapping in
the desired background image into this image plane it is possible to
interactively place the camera an image. This is valuable for making
sure the camera's angle matches that of the real camera.
A scene in Maya with an the background image plane attached to the camera
shadows you need to create a ground plane that matches the one in the
photograph. By renderning in seperate layers we can use the difference
of the ground plane with the ground plane with shadows to extract just
the shadow information. This can be done easily using the Difference
layer in Photoshop.
A scene in Maya with an the background image plane attached to the camera and a ground plane to reveive shadows
using these advanced steps you are able to create an even more
realistic looking composite. Keep in mind at this point the lights have
not been manipulated in position or placement at all from the default.
Rendered and composited image with all the stages of this pipeline plus shadows
Step 4: Dirtying up the image
this point you should be able to produce a pretty convincing high
quality render. However, the image will still need to be composited
into the background and "dirtied up" to make it look convincing. Above
is how the image looks with all of the elements combined before
dirtying up the image.
Launch Photoshop and open your image(s)
Blur and Noise work well for dirtying up the image
Render out as much as possible in layers so that it can be composited separately
Below is an example of this pipeline with the cg mock-up camera composited on top of the background image.
with any lighting setup there needs to be constant tweaking in order to
produce the best results. It should be clear that using just IBI alone
is not a very effective solution, but by stepping though this pipeline
it is possible to generate an accurate rendered image from using the
HDRI file as the base for all of the different lighting stages.
are some examples of the camera being lit through different lightprobes
(left) that are HDR images in angular format. The lighting is just
using the first stage of this pipeline to visualize the different
lighting aspects possible
Simon Bunker - a rendering guru with some excellent work and descriptions of HDRI CGTechniques.com - A site with several tutorials regarding HDRI OpenEXR - An open source format from ILM that supports HDR information