Built-in presets
Current preset - this dropdown list allows
you to choose from several presets for some of the irradiance map
parameters. You can use these to quickly set the color, normal and distance
thresholds, as well as the min/max rates. The following presets are
available:
- Very low - this preset is only useful for
preview purposes to show the general lighting in the scene.
- Low - a low-quality preset for preview
purposes
- Medium - a medium quality preset; works
fine in many situations in scenes which have don't small details.
- Medium animation - a medium quality
preset targeted at reducing flickering in animations - the
Distance threshold is higher.
- High - a high-quality preset that works
in most situations, even for scenes with small details as well as for
most animations.
- High animation - a high-quality preset
that can be used if the High preset produces flickering in animations -
the Distance threshold is higher.
- Very high - a very high quality preset;
can be used for scenes with extremely small and intricate details.
Note that the presets are targeted for a typical 640x480 image. Larger
images usually can do with lower Min/Max rates than those specified in the
presets.
Basic parameters
Min rate - this value determines the
resolution for the first GI pass. A value of 0 means the resolution will be
the same as the resolution of the final rendered image, which will make the
irradiance map similar to the direct computation method. A value of
-1 means the resolution will be half that of the
final image and so on. You would usually want to keep this negative, so that
GI is quickly computed for large and flat regions in the image. This
parameter is similar to (although not the same as) the
Min rate parameter of the
Adaptive subdivision image sampler.
Max rate - this value determines the
resolution of the last GI pass. This is similar to (although not the same
as) the Max rate parameter of the
Adaptive subdivision image sampler.
Color threshold (Clr thresh) - this
parameter controls how sensitive the irradiance map algorithm is to changes
in indirect lighting. Larger values mean less sensitivity; smaller values
make the irradiance map more sensitive to light changes (thus producing
higher quality images).
Normal threshold (Nrm thresh) - this
parameter controls how sensitive the irradiance map is to changes in surface
normals and small surface details. Larger values mean less sensitivity;
smaller values make the irradiance map more sensitive to surface curvature
and small details.
Distance threshold (Dist thresh) - this
parameter controls how sensitive the irradiance map is to distance between
surfaces. A value of 0.0 means the irradiance map will not depend on object
proximity at all; higher values place more samples in places where objects
are close to each other.
Hemispheric subdivs (HSph. subdivs) - this
controls the quality of individual GI samples. Smaller values make things
faster, but may produce blotchy result. Higher values produce smoother
images. This is similar to the Subdivs
parameter for direct computation. Note that this is not the actual number of
rays that will be traced. The actual number of rays is proportional to the
square of this value and also depends on the settings in the
rQMC
sampler rollout.
Interpolation samples (Interp. samples) -
this is the number of GI samples that will be used to interpolate the
indirect illumination at a given point. Larger values tend to blur the
detail in GI although the result will be smoother. Smaller values produce
results with more detail, but may produce blotchiness if low
Hemispheric subdivs are used.
Options
Show samples - when this option is on,
VRay will show visually the samples in the irradiance map as small dots in
the scene.
Show calc phase - when this option is on,
VRay will show the irradiance map passes as the irradiance map is
calculated. This will give you a rough idea of the indirect illumination
even before the final rendering is complete. Note that turning this on slows
the calculations a little bit, especially for large images. This option is
ignored when rendering to fields - in that case, the calculation phase is
never displayed.
Show direct light - this option is only
available when Show calc phase is on. It will
cause VRay to show direct lighting for primary diffuse bounces in addition
to indirect lighting while the irradiance map is being calculated. Note that
VRay does not really need to compute this. The option is only for
convenience. This does not mean that direct lighting is not calculated at
all - it is, but only for secondary diffuse bounces (only for GI purposes).
Detail enhancement
Detail enhancement is a method for bringing additional detail to the
irradiance map in the case where there are small details in the image. Due
to its limited resolution, the irradiance map typically blurs the GI in
these areas or produces splotchy and flickering results. The detail
enhancement option is a way to calculate those smaller details with a
high-precision QMC sampling method. This is similar to how an ambient
occlusion pass works, but is more precise as it takes into account bounced
light.
On - turns on detail enhancement for the
irradiance map. Note that an irradiance map calculated in this mode should
not be used without the detail option. When detail enhancement is
On, you can use lower irradiance map settings and
higher Interpolation samples. This is because
the irradiance map is only used to capture the general far-off lighting,
while direct sampling is used for the closer detail areas.
Scale - this determines the units for the
Radius parameter:
Screen - the radius is in image pixels.
World - the radius is in world units.
Radius - this determines the radius for
the detail enhancement effect. Smaller radius means that smaller parts
around the details in the image are sampled with higher precision - this
would be faster but may be less precise. Larger radius means that more of
the scene will use the higher precision sampling and may be slower, but more
precise. This is similar to a radius parameter for an ambient occlusion
pass.
Subdivs mult. - this determines the number
of samples taken for the high-precision sampling as a percentage of the
irradiance map Hemispheric subdivs. A value of 1.0 means that the same
number of subdivs will be used as for the regular irradiance map samples.
Lower values will make the detail-enhanced areas more noisy, but faster to
render.
Advanced options
Interpolation type - this option is used
during rendering. It selects the method for interpolating the GI value from
the samples in the irradiance map.
Weighted average - this method will do a
simple blend between the GI samples in the irradiance map based on the
distance to the point of interpolation and the difference in the normals.
While simple and fast, this method tends to produce a blochiness in the
result
Least squares fit - the default method; it
will try to compute a GI value that best fits in among the samples from
the irradiance map. Produces smoother results than the weighted average
method, but is slower. Also, ringing artifacts may appear in places
where both the contrast and density of the irradiance map samples change
over a small area.
Delone triangulation - all other methods
of interpolation are blurry methods - that is, they will tend to blur
the details in indirect illumination. Also, the blurry methods are prone
to density bias (see below for a description).
In difference, the Delone triangulation method is a non-blurry method
and will preserve the detail while avoiding density bias. Since it is
non-blurry, the result might look more noisy (blurring tends to hide
noise). More samples will be needed to get a sufficiently smooth result.
This can be done either by increasing the hemispheric subdivs of the
irradiance map samples, or by decreasing the Noise threshold value in
the QMC sampler rollout.
Least squares with Voronoi weights - this
is a modification of the least squares fit method aimed at avoiding the
ringing at sharp boundaries by taking in consideration the density of
the samples in the irradiance map. The method is quite slow and its
effectiveness is currently somewhat questionable.
Although all interpolation types have their uses, it probably makes most
sense to use either Least squares fit or
Delone triangulation. Being a blurry method,
Least squares fit will hide noise and will
produce a smooth result. It is perfect for scenes with large smooth
surfaces. Delone triangulation is a more exact
method, which usually requires more hemispheric subdivs and high Max
irradiance map rate (and therefore more rendering time), but produces
accurate results without blurring. This is especially obvious in scenes
where there are a lot of small details.
Sample lookup - this option is used during
rendering. It selects the method of choosing suitable points from the
irradiance map to be used as basis for the interpolation.
Nearest - this method will simply choose
those samples from the irradiance map which are closest to the point of
interpolation. (How many points will be chosen is determined by the
value of the Interpolation samples
parameter.) This is the fastest lookup method and was the only one
available in early versions of VRay. A drawback of this method is that
in places where the density of the samples in the irradiance map
changes, it will pick more samples from the area with higher density.
When a blurry interpolation method is used, this leads to the so-called
density bias which may lead to incorrect
interpolation and artifacts in such places (mostly GI shadow
boundaries).
Nearest quad-balanced - this is an
extension of the nearest lookup method aimed at avoiding density bias.
It divides the space about the interpolated point in four areas and
tries to find an equal number of samples in all of them (hence the name
quad-balanced). The method is a little slower
than the simple Nearest lookup, but in general performs very well. A
drawback is that sometimes, in its attempt to find samples, it may pick
samples that are far away and not relevant to the interpolated point.
Precalculated overlapping - this method
was introduced in an attempt to avoid the drawbacks of the two previous
ones. It requires a preprocessing step of the samples in the irradiance
map during which a radius of influence is computed for each sample. This
radius is larger for samples in places of low density, and smaller for
places of higher density. When interpolating the irradiance at a point,
the method will choose every sample that contains that point within its
radius of influence. An advantage of this method is that when used with
a blurry interpolation method it producses a continuous (smooth)
function. Even though the method requires a preprocessing step, it is
often faster than the other two. These two properties make it ideal for
high-quality results. A drawback of this method is that sometimes lonely
samples that are far-away can influence the wrong part of the scene.
Also, it tends to blur the GI solution more than the other methods.
Density-based - the default method; it
combines the Nearest and the
Precalculated overlapping methods and is very
effective in reducing ringing artifacts and artifacts due to low
sampling rates. This method also requires a preprocessing step in order
to compute sample density, but it performs a nearest neighbour look-up
to choose the most suitable samples while taking sample density in
account.
Being the fastest of the three methods, Nearest
lookup may be used for preview purposes. Nearest
quad-balanced performs fairly well in the majority of cases.
Precalculated overlapping is fast and in many
cases performs very well, but may tend to blur the GI solution. The
Density-based method produces very good results
in the majority of cases and is the default method.
Note that the lookup method is mostly important when using a blurry
interpolation method. When using Delone triangulation,
the sample lookup method does not influence the result very much.
Calc. pass interpolation samples - this is
used during irradiance map calculation. It represents the number of already
computed samples that will be used to guide the sampling algorithm. Good
values are between 10 and 25. Low values may speed the calculation pass, but
may not provide sufficient information. Higher values will be slower and
will cause additional sampling. In general, this parameter should be left to
the default value of 15.
Use current pass samples - this is used
during irradiance map calculation. When checked, this will cause VRay to
use all irradiance map samples computed so far. Unchecking it will allow
VRay to use only samples collected during previous passes, but not those
computing earlier during the current pass. Keeping this checked will usually
cause VRay to take less samples (and therefore compute the irradiance map
faster). That means that on multiprocessor machines, several threads will be
modifying the irradiance map at the same time. Because of the asynchronous
nature of this process, there is no guarantee that the rendering the same
image twice will produce the same irradiance map. Normally this is not a
problem at all and it is recommended to keep this option checked.
Randomize samples - this is used during
irradiance map calculation. When it is checked, the image samples will be
randomly jittered. Unchecking it will produce samples that are aligned in a
grid on the screen. In general, this option should be kept checked in order
to avoid artifacts caused by regular sampling.
Check sample visibility - this is used
during rendering. It will cause VRay to use only those samples from the
irradiance map, which are directly visible from the interpolated point. This
may be useful for preventing "light leaks" through thin walls with very
different illumination on both sides. However it will also slow the
rendering, since VRay will trace additional rays to determine sample
visibility.
Mode
Mode - this groups of controls allow the
user to select the way the irradiance map is (re)used.
Bucket mode - in this mode, a separate
irradiance map is used for each rendered region ("bucket"). This is
especially useful since it allows the irradiance map computations to be
effectively distributed among several computers when using
distributed rendering. Bucket mode
can be slower that the Single frame mode,
since an additional border must be computed around each region in order
to reduce edge artifacts between neighboring regions. Even so, there may
be such artifacts. They can be further reduced by using higher settings
for the irradiance map (the High preset, more
hemispheric subdivs and/or smaller Noise threshold
for the QMC sampler).
Single frame - the default mode; a single
irradiance map is computed for the whole image, and a new irradiance map
is computed for each frame. During distributed rendering, each render
server will compute its own full-image irradiance map. This is the mode
to use when rendering animations of moving objects. In doing so one must
make sure that the irradiance map is of sufficiently high quality to
avoid flickering.
Multiframe incremental - this mode is
useful when rendering a sequence of frames (not necessarily consequtive)
where only the camera moves around (so-called fly-through animations).
VRay will compute a new full-image irradiance map for the first
rendered frame; for all other frames VRay will try to reuse and refine
the irradiance map that has been computed so far. If the irradiance map
is of sufficiently high quality as to avoid flickering, this mode can
also be used in network rendering - each rendering server will compute
and refine its own local irradiance map.
From file - in this mode VRay will simply
load the irradiance map from the supplied file at the start of the
rendering sequence and will use this map for all the frames in the
animation. No new irradiance map will be computed. This mode can be used
for fly-through animations and will work well in network rendering mode.
Add to current map - in this mode VRay
will compute a completely new irradiance map and will add it to the map
that is already in memory. This mode is useful when compiling an
irradiance map to render multiple views of a static scene.
Incremental add to current map - in this
mode VRay will use the irradiance map that is already in memory and
will only refine it in places that don't have enough detail. This mode
is useful when compiling an irradiance map to render multiple views of a
static scene or a fly-through animation.
The irradiance map mode that should be used depends on the particular
rendering task - a static scene, a static scene rendered from multiple
views, a fly-through animation or an animation with moving objects. Refer to
the tutorials
section for more information.
Irradiance map control buttons
There are some more buttons in this group that allow one to perform
certain operations on the irradiance map:
Browse - this button allows the user to
select the irradiance map file which will be loaded if the
From file mode is selected. Alternatively, the
user can enter the path and name of the file directly in the edit box.
Save to file - this will save to file the
irradiance map which is currently in memory. Note that the
Don't delete option in the
On render end group must be turned on. Otherwise
VRay will automatically delete the irradiance map at the end of the
rendering process.
Reset irradiance map - this will clear the
irradiance map from memory.
On render end
This group of controls instructs VRay what to do with the irradiance map
at the end of the rendering process.
Don't delete - the default for this option
is on, which means that VRay will keep the irradiance map in memory until
the next rendering. If this option is cleared, VRay will delete the
irradiance map when rendering is complete. This means that you will not be
able to save the map manually afterwards.
Auto save - if this option is set, VRay
will automatically save the irradiance map to the specified file at the end
of the rendering. This mode is particularly useful if you want to send the
irradiance map for rendering on a different machine through network
rendering.
Switch to saved map - this option is only
available if the Auto save option is turned
on. If Switch to saved map is on, then VRay
will also automatically set the irradiance map mode to
From file and will set the file name to be that of the map that was
just saved.
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