In this tutorial we will render a walk-through animation of a static
scene, where nothing but the camera moves. We will use global illumination
to light the scene, which makes the task somewhat complicated. GI is usually
too slow to calculate from scratch and with sufficient quality for each
frame of the animation. To optimize this process and save rendering time, we
can use the fact that the scene is static and the camera is the only thing
that moves. Most of the GI solutions used in VRay (irradiance map, photon
map, light cache) are either fully or partially view-independent, and we can
use this fact to reduce rendering times.
For this tutorial, we will use the irradiance map as a primary GI engine,
and the light cache as a secondary engine. To make the process easier to
understand, we will render the scene in three steps.
In the first step, we will calculate the light cache for the entire
animation. In the second step, we will calculate the irradiance map. In the
third step, we will render the final animation.
Note that you don't have to use this method to render walk-throughs. You
can always use a slower brute-force approach and avoid having to deal with
all the issues around precalculating the various GI solutions. However, you
pay for this with render times.
1.1. Open the
starting scene.
1.2. Assign VRay as the current renderer.
1.3. Set the Background color in the 3dsmax Environment and Effects
window to RGB 252,252,252.
1.4. In the Render scene dialog, turn Global
illumination on and set both the
Primary GI engine and the
Secondary GI engine to
Light cache.
1.5. Set the Image sampler type to
Fixed for faster previews.
1.6. Turn on Show calc. phase in the
Light cache rollout.
1.7. Check the skylight Override MAX's
checkbox in the
Environment rollout.
1.8. Set the skylight color to RGB 252,253,255 and HSV(156,3,255).
1.9. Set the skylight color Multiplier to
4.0.
1.10. Uncheck the Default lights checkbox
in the
Global switches rollout. This will remove
the default max lighting in the scene and it will by lit only by the
environment skylight.
1.11. Go to the
Camera rollout and change the
Camera type to Fish eye.
1.12. Uncheck the Auto-fit checkbox,
change the Dist value to
1.0 and Curve to
0.35. We set the camera to Fish-eye to produce a more interesting
effect.
1.13. Render frames 0 and
360 for reference.
The light cache doesn't look bad, but we will need to calculate it
for the entire walk-through animation, and not for a single frame only.
Note that this is not strictly necessary - we can render the animation
with the light cache being calculated each frame; however, rendering it
only once will save rendering time, especially for long animations.
1.14. Set the light cache Mode to
Fly-through. Make sure that the timeline
animation range matches the range which you want to render. This is
important because the light cache will look at the current timeline
animation range when calculating the fly-through cache.
Since all the light cache samples will be distributed among all the
animation frames, we will need to increase the light cache
Subdivs value. The exact value depends on
the quality you want to achieve and on your specific animation. If the
camera moves slowly, or the path is relatively short (e.g. just one room
of a house) then you can use lower Subdivs
value, since most of the samples will fall in the same place anyways. If
the camera moves quickly or covers larger parts of the scene, you will
need more samples to get adequate coverage everywhere.
1.15. Set the light cache Subdivs to
2000.
1.16. Render frame 360 for example.
Note that although we render only one frame, the
Fly-through mode forces the light cache to be
computed for the entire animation:
During the fly-through mode, the preview display of the light cache
is not very useful, since it shows samples from the entire camera path.
The following image shows the preview display while the light cache is
being calculated:
Now that we have computed the light cache, we need to see if it is
good enough for our needs. We can do this by rendering several different
frames with the same light cache.
1.17. Save the light cache to disk, for example to
lightcache.vrlmap.
1.18. Set the light cache Mode to
From file and select the saved file name.
1.19. Change the Filter in the
Light cache rollout from
Nearest to None. Now
we can see better the samples' size.
1.20. Render frame 435:
You can notice that in places where the camera gets close to a wall
in the scene, the light cache samples are smaller and more noisy. This
is because the light cache Scale is set
to Screen by default. This is fine for still
images, but for animation we would like a more even sample distribution.
To achieve this, we will need to use the World
option.
1.21. Set the light cache Scale to
World.
Now we have to determine a good Sample size
for the scene. This can be done, for example, by creating a geosphere
directly in the camera viewport or a Tape object and using it to
visualize the sample size. For our scene, a sample size of about
2.0 seems to be good enough (the scene is in
Generic units). In general, you should make the
Sample size as large as possible without getting artifacts (light
leaks etc). Even if you are getting some light leaks, it may be possible
to remove them by reducing the filter Interp.
samples value.
1.22. Set the light cache Sample size to
2.0.
Keep in mind that when you use the World
scale, you must make sure that your scene is not too large (e.g. with a
large ground plane) or that the light cache samples are not too small,
otherwise you can run out of memory for the light cache. This is not
such a problem for the Screen mode, since
surfaces that are far away from the camera will get fewer samples
anyways. For exterior scenes, it is recommended to use the
Screen mode always.
1.23. Change the light cache Mode back to
Single frame and lower the
Subdivs to 500
just to check if the sample size is adequate. Here is an example of frame
435:
The samples are equal in size everywhere and they are just big enough
so we don't get artifacts on the image.
1.24. Set the light cache Mode to
Fly-through again.
1.25. To smooth out the light cache a little bit, increase the the
Subdivs to 3300.
1.26. Change the Filter back to
Nearest.
1.27. Render frame 360:
The calculation time is longer now due to the increased samples
number.
1.28. Save the light cache and set the mode to From
file again.
You may notice that the light cache file has become bigger in size.
This is because there are more samples in the light cache, partly
because of the World scale mode - the same
amount of samples are taken everywhere in the scene (in
Screen mode, the sample size increases as the
samples get farther from the camera, which leads to less samples).
Now we can render several different frames to make sure that the
light cache is adequate for our animation.
1.29. Render a few frames.
It looks like the light cache is good and we can move on to the next
part - calculating the irradiance map.
Compared to the light cache, the irradiance map may take significantly
more time to calculate. This is because the light cache provides a very
crude and undetailed lighting solution. The irradiance map, on the other
hand, takes care of the small GI shadows in the scene.
Note that the irradiance map cannot be calculated through backburner. It
must be calculated on a single machine. This is because we will use the
Multiframe incremental
Mode for the irradiance map.
2.1. Set the primary engine to Irradiance map.
2.2. Set the irradiance map Mode to
Multiframe incremental.
2.3. Check the Show calc. phase checkbox.
Since the camera moves quite slowly, there is no need to render every
single frame of the animation at this stage. We can get an adequate
irradiance map by rendering every 10-th frame, for example. If the
camera moves faster, we will need to render more frames, for example
every 5th frame.
2.4. Set 3dsmax to render every 5-th frame from the
Common tab of the Render scene dialog.
2.5. Turn on the Don't
render final image option in the
Global switches rollout, since we are not
rendering the final animation yet and we don't need the final frames.
2.6. Render the entire sequence.
2.7. Save the irradiance map to file, for example,
irmap.vrmap.
2.8. Set the irradiance map Mode to
From File with the saved file.
Now we have one irradiance map for entire animation sequence. We can
render a few frames to make sure everything is ok.
2.9. Turn off the
Don't render final image option.
2.10. Render frames 0 and
360 from the animation:
The two images above were rendered with the settings used for the final
animation in Part III.
Now we are ready to render the final animation.
In this section, we have added some questions about this tutorial that
were asked on our online forum, along with the respective answers.
Q: Did you render out to consecutive images and then compile the avi or
was it straight out to avi?
A: The animation was first rendered out to .png images, and then compiled
into an .avi. That way, you won't lose all rendered frames if something goes
wrong in the middle of the rendering... and also you can play with the
compression settings later.
Q: Why did you choose Multiframe incremental
over Incremental add to current map mode? What is
the difference between the two that would cause you to choose one over the
other? I ask because Ive never used Multiframe
incremental and have always used the Incremental
add to current map.
A: The only difference is that the Multiframe
incremental mode will delete the map in memory at the start of the
rendering. With the Incremental add mode, the
current map is not deleted.
Q: I just wanted to clarify... It is possible to use
Incremental add to current map mode in conjunction with backburner
without any problems (ie flicker)? Does backburner handle frame allocation
ok without max saving any files? Reading your post above, I get the feeling
you are suggesting that you need to send different sections of the animation
to each render-node.
A: Yes, you can render different sections on different nodes, but you
must merge the resulting irradiance maps manually with the irradiance map
viewer in the end, before rendering the final animation. Also, you must make
sure that each section is allocated to one single render node only.
Q: I must make an animation with a spray which you can see in the image
upload, and I have many glossy reflect and refract, if I follow your tut how
can I make my final setup? With lightcache for second bounce and
Use light cache for glossy rays or without
light cache and none for the second bounce? Does Use
light cache for glossy rays and irmap in first bounce work fine?
A: You can have the light cache saved with the irradiance map. If done
so, you can actually just turn off secondary bounces which will save memory
as you wont have to load the light cache. However, if you have the light
cache help precompute the glossies with the Use
light cache for glossy rays option, then you'll need to go ahead and
load the light cache when rendering.
Categories
VRay Resources
Your cart
Authentication
VRay News
