Irradiance Map VRay 1.5 tutorial

10 Feb, 2011 renderstuff (Staff Author)
This article is written for V-Ray 3d rendering plugin version 1.5. You may find that some particular interface options have different names, are implemented elsewhere, or not applicable for the newest V-Ray and another software. Regardless of that, current article is written in educational story style and can be useful for anyone interested in 3d rendering concepts and methods. To get the up-to-date interface manual for your software, please refer to the official documentation.

Hello everyone! We continue to setting up the global illumination in V-Ray. In the previous tutorial on the general setups and the principles of Indirect Illumination, we have learned what the global illumination is and why is it needed. In this tutorial, we will look into the principles, parameters and arguments for and against the calculation algorithms of secondary GI bounces Brute Force and Irradiance Map.

This tutorial answers the following questions:

- How does Brute force GI engine work?

- Where is the Quasi-Monte Carlo GI engine gone?

- How does the Irradiance Map algorithm work?

- How does the three-dimensional irradiance map look like?

- How IM detects the details of the scene?

- What is IM prepass?

- Why we should not set the same values of Min and Max rate?

- How does Detail enhancement option in the Irradiance Map work?

- What Multipass does?

- What value of interpolation gives smooth, but detailed Irradiance Map?

- Why there may be bright light spots on the rendering and how to get rid of them?

best v-ray engine settings 2.2 by renderstuff

Indifferent Brute force GI

Brute force GI is a basic algorithm that establishes a fixed number of rays reflected from a point in the scene after hitting it by original ray of light. If you remember, it was previously considered that the light ray from the light source falls on the surface of the scene object and is divided into a number of other rays, which in turn, bombard other objects of the scene (remember the example of the dandelion). Of course, the more diffusely reflected rays of the indirect light will the direct light ray be divided into, the more detail and less noise will be on the final image.

vray brute force gi subdivs 8 secondary bounces 3
Screenshot of a roolot V-Ray:: Brute force GI of a Indirectc illumination tab of the Renders scene windows of main 3ds Max rendering options. Here present twor parameters: Sebdivs and Secondary bounces.

Subdivs is a parameter trivially influencing the number of reflected rays, to which every original light ray splits, when it reflects from the object of a scene. Numeric value Subdivs it is not the actual number of such secondary rays. The actual number of rays will be equal to the square of that number. That is, if Subdivs is 2, then this means that the original light ray will be divided into four rays after reflection; if it is equal to 4, the original ray will be split into sixteen secondary and so on.

Secondary bounces is the value that specifies how many times will the secondary rays interreflect further. It is active only if the Brute force algorithm is set as an algorithm for rendering Secondary bounces in the corresponding dropdown list, because in this case, it will calculate the right amount of interreflections. If the Brute force is set as a Primary Bounces GI engine, the Secondary bounces parameter will be inactive.

Brute force algorithm is not adaptive, and simply calculates the GI for each pixel of the final image of the scene, not depending on its complexity, color and detail of objects. Thus, it spends the same amount of computing resources, both in clearly visible and in the unimportant parts of the scene. No wonder why it was named brute force :) We would also like to note that the Brute force is a direct calculation by the method of Quasi-Monte Carlo (QMC) and that is how it was called in earlier versions of V-Ray, which sometimes caused confusion when 3d artists have been long looking for a Quasi-Monte Carlo GI in the new interface.

The brute force of this algorithm is very irrational; its use leads to monstrous times for calculation, even on simple scenes at an adequate level of quality. Therefore, it is not worth to nominally use it in universal V-Ray settings as the render engine for primary or secondary bounces. Its use is justified only in special situations where other algorithms, because of their adaptability cannot cope with the calculation of small details in the scene, but more on that later.

Adaptive Irradiance map

Irradiance map is an adaptive algorithm of rendering global illumination bounces. The main feature of its work is to identify the most important areas of the rendered scene, calculate GI there and fill the GI information about the omitted areas by interpolating the information from the already computed ones.

In order to understand how works and what algorithm Irradiance map is, let us look at generated by it map, which, by the way, called the same ­­– irradiance map.

rendering vray irradiance map samples cube shpere room
Rendering of the test scene with the visible Irradiance map samples. This image showes the number of the white dots, which represent the GI samples. The detailed areas have more of them, while the flat surfaces have only few on a great distance between each other.

In front of you is the test scene, which was used in the previous tutorial about the GI, with the same geometry and the same direct lighting as before. For clarity, were removed all textures from the scene materials, to not to obstruct the observation of the irradiance map. Look closely at the most crowded with white dots areas. This is the interior angles of the room, rounded ChamferBox angles, and places of close to each other parts of different objects, in particular on the side of the sphere facing the cube, as well as the contact area of a cube with the front wall. These zones have the greatest importance in obtaining beautiful detailed global illumination.

It is set of these points is the irradiance map, which we see on the image. These points contain information about the color and brightness of GI in those exact areas. The rest of the image is filled with gray color. Gray areas on the irradiance map is part of the scene where irradiance map contains no information about GI. However, it is fully compensated by interpolation between the already computed points of irradiance map. In other words, Irradiance map calculates the most important areas only. After this, the missing information on areas, which were not computed, it simply compensated by interpolation, taking information about the color and brightness from the already existing ones.

It is quite obviously, what the adaptability of the Irradiance map is. In contrast to the Brute force (BF), Irradiance map (IM) does not calculate each pixel of a scene. It calculates only important areas, because of what the very significant savings of computing resources is possible.

Irradiance map algorithm builds a three-dimensional map of points, containing information about the GI just on the surface of objects in the scene. In the volumetric view, the irradiance map of our example scene looks as follows:

irradiance map viewer volumetric samples absence of not visible parts
The volumetric look of the Gi irradiance map produced by Irradiance map rendering algorithm. Here may be seend the actuad 3d-ness of the GI map and the disturbing of the samples. There are no samples at all at unvisible to camera scene geometry.

If we look at shown above second and third screenshots from special utility called Irradiance map viewer, we can clearly see not only the fact of three-dimensionality of irradiance map, but also its dependence on the view of camera, through which the rendering of the scene is performed. In particular, immediately striking eye the lack of points on the GI on not visible in the camera frame parts of the cube and on the other side of the room, which is located behind camera.

vray rendering total animation current task prepass 1 of 4
Screenshot of the Rendering window that pops up and stays along all rendering process. Here showed the Current Task of the IM calculation. Exactly is is a Prepass 1 of 4 means that the first of total four prepasses is performing at the moment.

In IM "feeling for" the important places of the scene in which GI calculation is performed, is implemented a very elegant way. It uses the concept of undersampling, previously described in the first tutorial of a Best V-Ray Settings series. For a start, GI of entire scene is calculated in the lowest resolution, which is usually less than the rendering resolution. This calculation is just not adaptive, as calculation with BF algorithm. After that, from the obtained data, the most important areas are determined, that is evaluating the very same areas where the more accurate rendering should be performed. Then the next higher resolution rendering takes place, but only in the required areas. This procedure is repeated several times step by step, each time increasing the resolution, and so, until it reaches the maximum specified resolution of the IM. The minimum and maximum resolution of IM rendering are set in its parameters. The step of calculations differs in twice more or twice less resolution, which is four times by area of the image in pixels. For example, when rendering resolution is 800 by 450 pixels, the next step of undersampling is 400 by 225, the next one is 200 by 113 and so on. It is worth noting that IM can use both the undersampling and supersampling. That is, IM can be calculated on less and on larger than the actual rendering resolution, in an even number of times, resolutions.

Each phase of the GI rendering called pass. The pass, which determines the important areas of the scene, called Prepass. The progress of passes calculation, their total number, and what prepass is calculated at the moment, can be observed in the Rendering system window, which pops up after starting the rendering.

Let us see, how IM calculation looks like on the example of four prepasses.

im prepasses different rates different sampling resolution
Four renderings vith visible samples. There are four step by step prepasses of Irradiance map. The first one has no higher density of samples in detailed parts of the scene, while others have them. The last fourth prepass shows the final samples distribution on the irradiance map. All renderings have showed IM resolution.

In this example, the maximum resolution of IM rendering is a resolution of 800 by 450, equal to the resolution of the rendering of the final image. To fully identify important areas, first used three undersampled prepasses at lower resolutions: 100 by 56 in the first prepass, 200 by 113 in the second prepass, and 400 by 225 in the third. Together with the final prepass, there are total four IM prepasses.

Look at the first prepass. You may notice that it had not allocated any areas, the entire image calculated equally with the same accuracy as the BF algorithm does. But completely different picture can be seen already at the third and especially the last fourth prepass. It is clearly apparent how the IM algorithm highlighted the important details of the scene, strewed them with GI samples, and significantly thinned out flat not detailed surfaces. They are unimportant the parts, such as walls planes, the flat face of the cube, etc. They have only a few points that will later be simply interpolated between them by IM algorithm, filling the empty zones. Also, we can immediately see that the size of samples with respect to the entire image at different prepasses is different, because the higher the IM rendering resolution, the lower the value of a single sample, and so more detail and more accurate irradiance map is.

It is not hard to guess that GI map, calculated with IM even on the full final resolution without advance prepasses, so without calculating the important areas will be just as tough and not adaptable, as in the case of GI rendering using the BF algorithm. The time to calculate it will certainly be nearly as long, as in the case of BF.

irradiance map with single prepass very dense
Rendering if the test scene with the visible IM samples. It may seem that here no samples at all. But in fact all image consists of dense situated samples. They are equally placed on the detailed parts as well as on the not important flat homogenous surfaces.

This image shows the irradiance map, calculated by one prepass right at the final resolution. When looking at it, it seems that there are no samples at all. However, it is just the opposite. All that is seen in this picture, these are all samples, very tight-studded the each pixel on final resolution. Thus, the irradiance map is not concentrated in some important areas; it completely covers all scene objects visible from the camera. Obtaining such a dense map entails such as many calculations. In particular, all four prepasses in the first case were calculated in 5 minutes, while calculation of only one pass in the second case took 50 minutes of computing time. The difference is more than obvious. Make no mistake that in the second case, the quality of the final image will be substantially better than in the first, because of richer map. The fact is that the unimportant areas of the scene represent mostly flat surface of one color; the color of GI there, is homogeneous and without details in both cases. However, important areas of the scene, in fact, that were calculated with and without adaptation, are equally detailed. That is why there is no point in spending ten times more computing resources on rendering homogeneous flat surfaces to get essentially the same result. We believe that the scale of time saving, when calculating the with IM, comparing to the time of calculation with BF, is quite obvious.

When the map of important points that contain the GI color information, has been calculated, the interpolation of missing GI points is starting. Then on rendering, in each point, as in the case of BF, performed calculation of a fixed number of secondary light rays over the hemisphere, as described in the previous tutorial.

Basic Irradiance Map settings

For that, which areas algorithm IM considers important, the number of secondary rays will take each point of IM, as well as the resolution of the probing details of the scene, respond the parameters located in the V-Ray:: Irradiance map rollout.

vray irradiance map built-in presets basic parameters detail enhancement advanced options mode on render end
Screngrab of the V-Ray:: Irradiance map rollout of the Indirect illumination tab of the Render scene 3ds max window. Here are much parameters. The fisrs Built-in presets area has only drop-down list Current preset. Basic parameters zone contains parameters such as Min rate, Max rate, HSph, Subdivs, Interp. samples, Clr thesh, Nrm thresh, Dist. thresh, Interp. frames. Options zone is with Show calc. phase, Show direct light, and Show samples parameters. Thre are slo such zones as Detail enhancement, Advanced options, Mode, and On render end.

Current preset is just a quick set of preset values for the main parameters of IM. Dropdown list with these sets is in the Built-in presets zone. The purpose of each of them can be easily understood by their names, they speak for themselves: Very low, Low, Medium, Medium animation, High, High animation, Very high. However, the greatest interest to us is Custom option. As its name implies, this value allows us to manually configure IM. Feature of Current preset option is that if you select one of the presets, and then select Custom, then numeric fields of IM parameters will keep the values of the last preset. By default settings, IM is preset to High, it is this preset we should choose for the start and then change the basic parameters of the IM, selecting the Custom.

Next, the Basic parameters zone options come. These are obviously the basic IM parameters.

Min rate is a value that determines the resolution of the first prepass of GI.

Max rate is a value that determines the final resolution of rendering GI or simply the resolution of the last prepass.

As we already know, the IM algorithm with a few GI calculation steps selects the most important and detailed areas. If you look at the examples above, in the upper right corner you will find the value of rate, which determines the resolution of current prepass in rendering IM. Rate value 0 (zero) means that the calculation of GI will be in a resolution equal to the resolution of the final rendering. Rate value equal to -1 means that the calculation of GI will be in a twice lower resolution than the resolution of the final image. Rate value equal to -2 means that the calculation of GI will be in a twice lower resolution than the resolution of -1 rate, which means four times less than the final image resolution. By analogy, the rate value equal to 1 would mean that the calculation of GI will be doubled comparing to resolution than the resolution of the final image, etc.

Absolutely similar concept of undersampling and supersampling uses the anti-aliasing V-Ray Adaptive subdivision algorithm, discussed in detail in the first tutorial of the best V-Ray settings.

Algorithm Irradiance Map is a very flexible and high-tech tool. Despite the seeming logic of rendering the final GI prepass on the final resolution, i.e., with Max rate equal to 0, in practice there is absolutely no need to do this because of the small difference in quality, and the huge difference in computational cost.

The following examples illustrate this:

im calculating time high and lower min and max rates significant time saving
Renderinf of the test scene with different Min and Max rates. The first rendering shows beautiful image with the long rendering time. While the second rendering shows the quite acceptable image quality with the 5 times less rendering time.

On the first image, where the IM has been calculated on the final resolution of the rendering there is a little more clear and dense shade under the sphere than on the second image, as well as more precise and sharp shadow at the bottom of the cube, especially seen in its left corner. This is because in the first case, IM has a lot of small details, while the latter are interpolated from a smaller IM resolution. However, the render time of IM in the first case (max rate: 0) by more than 5 times greater than when the last prepass was calculated at 8 times lower resolution (max rate: -3). Five minutes and three seconds against fifty-seven seconds. At higher resolution and more complex scene, the time difference calculation IM will be even greater. At the same time, at high resolutions such as 2500 – 3500 pixels by a side, which is by the way should be used in the final rendering, this difference will be less noticeable due to the overall resolution increase. In addition, this slight and pale blur of details in a few minutes elementary eliminated in 2d graphics editor. In practice, the values of the Min rate -5 and Max rate -3 is sufficient for the good photo-realistic rendering, and these values should be set in start V-Ray configuration.

Parameter HSph. subdivs (in a more expanded form HemiSphere Subdivisions) is the number of rays of GI, reflected from a point on the surface of the object. This parameter determines the amount of diffuse light rays taken of each secondary point IM, as mentioned earlier, in the form of a hemisphere. That is a complete analog parameter to a Subdivs in BF algorithm. In most cases, the HSph. Subdivs value, equal to 80 is enough and that it should be set for universal V-Ray configuration.

Interp. Samples is the parameter that determines the quality of interpolation of the IM. Remember the examples with IM samples, where the samples were marked with light dots, and missing areas with gray color. Interp. samples determines the quality of interpolation of not important gray areas with missing information, from the white-dotted important areas. The higher the value of Interp. samples, the higher the interpolation, resulting more blurred GI, while at low values of Interp. samples GI map is less "soapy", but more noisy with lots of artifacts. Default value of 20 samples is enough, and this value should not be changed.

As we already know, IM with help of prepasses feels for to the scene to identify its most detailed parts. IM does so, based on previous prepasses information, and it is guided by three main critical in terms of details properties. This is color, difference between the normals, and the relative position of objects. In the IM, these properties are presented with Clr thresh, Nrm thresh and Dist thresh parameters respectively.

Clr thresh determines the sensitivity threshold of the algorithm IM to the colors of the scene. The higher the threshold, the less color changes on the objects of the scene will be considered as important areas and the easier will be the calculation of IM. Lowering the sensitivity threshold of the algorithm will make IM more sensitive to color changes in the scene and would create more detailed IM, and so the better pictures. Clr thresh parameter value equal to 0.3 is quite acceptable to create an acceptable IM and in universal V-Ray settings we should use it.

Nrm thresh defines the sensitivity threshold of IM algorithm to the scene geometry, in particular to the intensity of change of the object’s normals in it. The lower the threshold, the more geometric details on the objects of the scene will be considered as an important area, respectively, higher quality will be the final image. The parameter Nrm thresh equal to 0.1 is enough for a well-detailed IM and it should be used in universal V-Ray settings.

Dist thresh defines the sensitivity threshold of the IM algorithm to neighboring geometric surfaces in the scene. The higher the threshold, the farther each to other surfaces will be considered as an important area and better will be the final image. Looking at the showed above example, you can easily understand the difference between parameter Dist thresh and parameter Nrm thresh. If from Nrm thresh in this scene will depend the density of the IM in the corners of the room, then Dist thresh will determine the detail of IM in the zone of the close location of the sphere and cube to each other. It should be noted that, when the threshold Dist thresh is lowered, it will take into account only the smaller distance between the surfaces of objects, thereby reducing the density of the samples of IM, and hence the quality of the final image. Pay attention that it is in contrast to the Clr and Nrm thresh, where the decrease of threshold improves image quality. The parameter Dist thresh of 0.1 is enough to create a good IM and we should use it in universal V-ray settings.

The last parameter, located in the zone of Basic parameters, it is inactive Interp. frames. It is responsible for a number of irradiance maps, calculated for different frames of animation in the mode of Animation (prepass), which V-Ray will use to render the current frame in Animation (rendering) mode. It is in the last case, this option will be active and available for change. However, these are very specific modes of IM, which will be described in the tutorial on rendering various types of animation in the V-Ray. By default, in the universal V-Ray settings this option may be left unchanged.

In Options zone of the V-Ray:: Irradiance map rollout can be enabled options, which are responsible for IM rendering in the frame buffer. These options enabling let us to observe clearly the IM prepasses calculation, to show direct light with the GI on the prepasses rendering and to watch the location of samples on the IM. For these functions response parameters Show calc phase, Show direct light and the Show samples, respectively. These are all test functions that do not affect the IM rendering, and in the universal starting V-Ray settings they should not be activated.

Irradiance map detail enhancement

The next area of IM parameters is the Detail enhancement.

As we know, the main highlight of IM is the calculation of important details of scenes with prepasses at lower resolutions. Option Detail enhancement allows us to create a hybrid between an adaptive, but making a little fuzzy samples map IM algorithm and a rough, but precise in details, Brute Force.

When the function Detail enhancement is activated, IM, as well as before, uses prepasses to calculate the details of the scene. However, at the last calculation pass, when the final information on the detail in the scene is obtained, the algorithm Detail enhancement comes into play. The principle of Detail enhancement work is that GI samples of the most important areas are calculated by the algorithm Brute Force at full resolution of the final rendering, without undersampling. All other areas, as in the normal mode of IM, are calculated by interpolation.

The algorithm of Detail enhancement for the determining of what samples in important areas should be calculated, based on the principle of the algorithm similar to the Ambient occlusion (AO), but, in contrast to AO, Detail enhancement algorithm takes into account the direction of light.

It is worth to note that when Detail enhancement is activated, IM algorithm is used only to determine the detail of the scene, and direct rendering of important details lies on the BF component of Detail enhancement. Knowing this, if the option Detail enhancement is active, we can lower all the parameters of the IM, except Interp. samples. Parameter Interp. samples can even be set to larger values.

Algorithm is activated by setting the tick in the checkbox On. Then become active settings such as Scale, Radius and Subdivs mult.

Scale defines the units of measurement of the following Radius parameter.

Radius is the value of the hemisphere radius, which defines the area in which the BF will calculate the GI samples from the reference point. Location of reference points of BF, as mentioned above, is determined at the stage of calculations of detail of the scene with prepasses.

Subdivs mult. is in fact a complete analog of Subdivs parameter of the BF algorithm, which determines the number of diffuse rays. It is set as a percentage of the current HSph. subdivs value.

To better understand what is the radius of the hemisphere, and what hemisphere point we are talking about, we should be closer acquainted with the concept of AO. Explanation of this concept is beyond the subject of this tutorial, but it will be discussed in detail in separate article on AO and, in particular, areas of application of the parametric VRayDirt map. In any case, Detail enhancement is a specific option, which greatly reduces the adaptability of IM and significantly increases the time of GI rendering. That is why it should not be activated unnecessarily and, of course, in the universal V-Ray renderer settings also.

Additional Irradiance Map options

Next in the IM settings is a zone of Advanced Options.

Interpolation type is drop down list that allows us to choose the method of interpolation if IM samples, i.e., the algorithm that fills the missing areas in the IM, getting the absent sample data from already computed ones. This list contains four methods, they are Weighted average (good / robust), Least squares fit (good / smooth), Delone triangulation (good / exact), and Least squares with Voronoi weights. Technically, they have different mathematical principles to calculate the result. It is absolutely no need to delve into how they work. End user need only to look at the clues given in parenthesis at the end of each of them, and immediately become clear about their features. Optimal interpolation method is the default Least squares fit. That is it worth using in the starting V-Ray configuration.

Sample lookup is a drop-down list, allowing us to select a method that determines which of the calculated IM samples will take part in the interpolation of missing samples in the surrounding areas. There are four sample selection methods, they are Quad-balanced (good), Nearest (draft), Overlapping (very good / fast) and Density-based (best). These also are algorithms, each with its own mathematical peculiarities in the methods of selecting the desired samples, in which it is not necessary to delve without special need. Similarly to the  Interpolation type methods, the tips in parenthesis next to their name perfectly explain their features. By default, the best method of Density-based (best) is set and exactly it we may use in universal V-Ray settings.

Calc. pass interpolation samples - a value that specifies the number of computed samples that will guide the IM interpolation algorithm during the last calculation pass. Nominally assigned value of 10 samples is enough to get good results. It should be used in universal settings of V-Ray.

Multipass is a feature that allows the current IM prepass to be able to use absolutely all available samples, calculated for the current particular moment. That is to say, the samples from previous lower resolution prepass, and samples that are already computed in the current own prepass.

Irradiance map is computed as the final render, in many threads to fully utilize the potential of modern computing systems, which are often multi-threaded through multiprocessing and multicore. Initially, when calculating IM by multithreaded system, every piece of IM is calculated by a separate thread, independently each from other. The data for this calculation is taken only from the previous prepasses. Because of this, it turns out that each piece of calculation of IM, without information about the surrounding portions gives inconsistent with them results. On the calculated in this manner IM become evident the boundaries of those portions in the form of lattice.

vray irradiance map rendering visible sample rendering portion boudaries multipass off
Rendering with the turned off Multipass function. It demonstrates that the obtained this way IM has evident lattice formed by rendering portions, that were not matched.

Look closely at the picture. There are clearly visible linear boundaries of IM calculation per-thread portions. For example, this effect is very noticeable on the sphere and on the wall to the right, on the ceiling above the cube.

Enabling of Multipass function allows the IM algorithm to use information about the current prepass samples. That is, when rendering each portion, it allows the IM algorithm to use information about the adjacent calculated portions, giving a consistent smooth result. Thus, in practice, Multipass function allows to smooth the boundary between the IM calculation portions, giving homogeneous IM, without any visible artifacts in the form of a lattice. In the universal starting V-Ray configuration, this function should always be kept active.

Randomize samples is a feature that allows to generate samples of IM in a random order, making IM more realistic. Nominally, the IM algorithm selects the samples on scene objects with regular intervals, resembling a grid, even if the considered above option Multipass is enabled. This effect clearly can be seen in the image below.

test scene vray rendering im ordered samples with randomize samples option off
Test scene rendering with the turned off function Randomize samples. It shows that by default, IM samples are placed with the predictable order, which can lower the photo-realism of the obtained image.

To resolve this regularity, which betrays the computer origin of the image, and prejudices photorealistic renderings, function Randomize samples in universal V-Ray settings we surely must keep activated.

Check sample visibility is a feature that allows us to interpolate the samples of IM, only being in sight of each other. Very often, due to the low density of IM, in the process of interpolation of missing samples, the IM algorithm takes the neighboring samples that fall within the zone of sampling for a given point, even though they may be located outside the visible area relatively to each other in the scene. For example, we have a bookcase with a thin wooden shelf, lying close to the rear of this bookcase. On the top of the shelf is a light and it illuminates shelf’s upper part. Under the shelf, direct rays of light in no way can fall. Nevertheless, beneath a shelf at the rear can easily appear bright spots, despite the fact that they simply cannot be there. This happening because the IM algorithm to interpolate the missing samples in the area below the shelf, takes adjacent samples from the upper part of the shelf, without considering actual geometry. To avoid this, the IM interpolation algorithm is necessary to know that we want to check what samples are in the zone of direct mutual visibility, and what are not. Of course, such a check would require additional computational resources.

We suggest you to look an example from V-Ray Help, which perfectly illustrates how this function works.

This is a very useful feature, however, in most scenes, the above-described artifacts are absent, and there is absolutely no need to always verify visibility of samples, needlessly wasting computing resources. In the universal starting configuration of V-Ray, feature Check sample visibility should be disabled.

In areas Mode and On render end we can set the IM working mode, needed for animation rendering. We can specify a folder and name on the hard drive, under which the computed IM can be saved. As mentioned earlier, to the animation in V-Ray a separate tutorial will be devoted, in which these options will be discussed. In starting universal V-Ray settings these options should be left untouched as they are by default.

One last thing worth noting is that the algorithm Irradiance map can be used only for rendering the first diffuse bounce, that is, only as a Primary bounces GI engine. From the working algorithm of IM it is quite clear that the calculation of the avalanche of GI rays, produced after the first bounce, the methods of IM prepasses are inappropriate. When choosing Secondary diffuse bounces GI engine, in a V-Ray:: Indirect Illumination (GI) rollout, an Irradiance map option is absent, which excludes its use for these bounces in any case.


In this tutorial, we have thoroughly been acquainted with important aspects of setting two GI rendering algorithms, namely, the Brute Force and Irradiance Map. In particular, we exhaustively investigated all the details, aspects and tweaks of adaptive GI rendering engine Irradiance Map, and clearly were able to see everything on numerous examples.

Dear friends, we sincerely hope that after carefully reading this tutorial, you are much closer to understanding the essence of the Brute Force and Irradiance Map. We also hope that you are no more scared by a lot of IM settings, and their technical names do not mislead you anymore. Understanding of this critical information lets any V-Ray user easily customize and obtain great GI maps for photo-realistic 3d renderings.

In the next tutorial, we will learn about the GI bounces rendering algorithms Photon mapping and Light Cache. We will consider in detail how they work and each function of Light cache in particular, will learn about the best values of their settings.

All have easy settings and beautiful 3d renderings!

12 Feb, 2011 voron81
12 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Spasibo! Ochen poznavatelno!

13 Feb, 2011 Aleksey
13 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Thank you for this analysis! This is a very useful thing! Just wanted to ask a question! You are not told about the preservation of IM. The fact that it is possible to reduce the waiting time if you save kartuIM. and would like to know about the "myth" - if you calculate the IM at low resolution, you can slip it in large? If you analyze your writing, it can be done if the rate value to inflate the value of a ...?

13 Feb, 2011 RenderStuff (Staff Author)
13 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Hi Aleksey. Of course, IM card can be saved, and then safely load and calculate the final render at a resolution greater than that which was carried out the initial miscalculation of IM. However, the rate The parameters, as described in detail above, it is, in fact, and have permission to render IM. Excess save operation to the hard disk just to anything. If the essence of this myth is to calculate the IM map on one resolution, and then increase the rendering resolution and use this card, but this initially makes no sense, because once it is possible to calculate the IM at the desired resolution, specifying true value rate. If from the beginning to make the image rendering to final resolution, and Max rate to put a lower value, the IM map, of course, it has been calculated at a lower resolution. That will have a similar desired result without the hassle of loading and unloading IM map, it is easier and wiser😉

13 Feb, 2011 Aleksey
13 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Well, yes, I agree ... thank you! And you can add IM? That is, think IM for one camera then IM to another camera ... folding or "dosohranyaesh" ... thus it is possible to even further improve the details to a minimum and to Reith? I think it would be faster 🙂 although maybe stupidity ...

13 Feb, 2011 Aleksey
13 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
We look forward to continuing a very ... 🙂

13 Feb, 2011 RenderStuff (Staff Author)
13 Feb, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Stack stored on the card drive costed from different cameras, into one big map of IM can be, for example, by using a special utility. You can immediately and automatically make it Vray means. You can even render one camera, and then later when rendering, to count only those scenes zones for which the IM has not been calculated, thus saving computing resources already counted 🙂 But, as already mentioned in the lesson about this later in a separate article dedicated to rendering animations of different types of V-Ray.

2 Mar, 2011 Vladimir
2 Mar, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Hi, thanks for this analysis settings have not enough understanding of the basics!

11 Apr, 2011 Ilya
11 Apr, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Excellent article! Really looking forward to the next lesson about the animation !!!

5 Aug, 2011 ASRockus
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Uv. RenderStuff, decided to experiment with the settings recommended Vami.Sozdal scene as you have in the image below, the light in VrayLight okne.A Now the problem: without a GI scene is illuminated for some reason not as your, back sphere to the wall where its shadow falls and the shadows of the cube dirty black spot, and she half-sphere of the same tsveta.A-enabled GI shadows on the wall are very noisy. I would like to hear at least a suggestion. With respect!

13 Feb, 2011 RenderStuff (Staff Author)
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Hello! You wonder confused 🙂 You're all quite normal turns. Just you have a much larger VRayLight Plane, as well as the cube itself is almost the same height with the scope. In this part of the sphere is illuminated by direct light falling on it directly from VRayLight. Zoom size Lite or increase the height of the cube and you'll get the same effect with the "invisible" area😁 Also, if you look closely at the article screenshots - you will see that chemfer box there is not only higher than yours, but also significantly longer in the side of the camera😁 When you turn of Global illumination , as actually and without it, simply continue to make noise VRayLight. Merely because the default the Subdivs 8, determine the quality of the shadows cast by this light source is very low. Raise Subdivs to 30 - 40 and the noise in the shadows disappear😉

5 Aug, 2011 ASRockus
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
VRayLight Plane with aperture size okna.I you well on the screenshot to the lesson so ugly black dirt net.Vasha Sphere is in complete darkness with a soft (so to speak), but I have a dirty black polosa.Kak you posvetovali VRayLight have raised up to 30 subdiv cube has increased in size with the included GI noise vsyotaki not completely disappeared here's a look-enabled and non-GI:

13 Feb, 2011 RenderStuff (Staff Author)
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Of course not completely disappeared. But all in your hands. Spin up to 60 & or higher, as well as the Screw LC and IM. So you will be able to achieve complete absence of visual noise. Regarding the darkness, then that is what chemferboks chemfer him to have been bevelled edges 🙂 If you look like your chemferboks adjacent to the wall, you will see where the light breaks. For you not to bother, reducing or filet radius vdvigaya chemferboks the wall, just replace it with a normal Box and tightly Pridvin'e the box to the wall, to avoid gaps, you can even slightly Push inside its walls that for sure. Not only one renderer settings are important for visualization. The geometry of the scene also plays an important role in achieving the desired result😉

5 Aug, 2011 ASRockus
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
With noise to render with GI clear as possible and twist all that is (LC, IM, etc.), but that's how it will be rational, because most likely render time will increase as the ear! and all this in a simple scene, and that would be draped with material, imagine scary. Chamferboks replaced the cube, pulled up to the wall so that no light will break😉 but no change. It wants to understand the cause of this pseudo-black shadows and achieve similarity with your skrinom.Prostite for my intrusiveness (age)😉

13 Feb, 2011 RenderStuff (Staff Author)
5 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
In general, it is not clear what exactly you do not like? The last option looks great with both GI and without it. Without GI looks exactly as it should. Carefully read the second lesson series about the best settings-Ray the V: In particular the chapter "Global illumination in computer graphics." There is quite clearly seen that the "shadow". Your renderings look quite similar to 🙂 Concerning rationality, it should be understood that the situation white scene with white geometrical shapes - a completely synthetic. In real 3d rendering scene will be with materials and textures that are completely hide all the artifacts. Put in the diffuse slot of his white stuff any texture, for example, a wood texture and you will see that the noise has virtually disappeared. He certainly remains the same, just on a background texture will not be noticeable. Also, for the purity test, do not forget about boxing shape. We have it is deeper and greater than you😉

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Now something has become clear, namely, after I decided to keep render the image in a graphical format, and show you that it does not suit me, I saw to my surprise that the picture began to look better. Gone was this dirty black stripe (ie, it is, but not the same as before) and klyaksovye spots are seen on the screenshot made in a viewport, all became much softer! So, what we see right after rendering (without saving in graphics format) this is not a complete picture? By the way, it is darker than Max (why?). If so, then confirm or disprove my suspicions. GI is included and stored in JPEG image and this without GI

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
You're here: Gamma 2.2 will tell you all the details😉

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
And on the image to save Max and then, what do you say? Why are all the same, some artifacts simply disappear after the image is saved in a 2d format?

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Thank you for taking part in uv.RenderStuff my experiments, so to speak. Much grasped and more proyasnilos.Esli any more questions, you can contact? Thanks again.

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Of course! Be sure to ask, we are happy to help you😉 Especially for these purposes we have a mini-forum on 3d graphics: Feel free to come in and ask a question of interest to you. If there is no appropriate topic, then open the new one. Regarding the image to save Max and after - read about the range of article 2.2 from the link above. There is an answer to your question 🙂

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Regarding image Max, you do not quite understand correctly, I mean: why some artifacts disappear after you save into graphical format? On the screen above it shows that you have vvidu.Tam where red painted this picture of Max-screen rendering (namely screen), and below pictures the same render BUT already saved in JPG format from the Max window in the usual way (save as). Do not know if it is clear ... expressed in the article gamma about artifacts like there is nothing, in any case, re-read again, but like everything else there, a huge thank you again!

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Yes, indeed, we do not quite understand you right, but getting to the point, the picture in the frame buffer is usually interpolated, that is, it is shown not to scale pixel-to-pixel, and a slightly reduced. Sometimes this interpolation (because of the reduction), can appear seemingly artifacts, which actually is not😉

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
I wonder how then to monitor this "process" ?, because really would look like a picture, you can see only after saving.

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Hold Ctrl to point and click the mouse in the window frame buffer. Or simply twist the wheel on it, so you can zoom display rendering in the frame buffer to the one you want, as well as examine closely all the details you are interested in. Also, of course, you must always use the V-Ray frame buffer, and not properly working with the V-Ray - standard maksovsky 🙂

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Regarding the V-Ray frame buffer, if there click on the icon "clone", it opens Maksovsky, and in it the image lighter (it is clear that the scale), but as if to make a clone, so that later, after further any amendments or adjustments it was possible to compare the results?

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Keep the render to disk and compare the results, leafing through some one else imeydzh file viewer 🙂 The V-Ray 2.0, for example, generally has a new feature VFB the History , which allows you to compare the previous and new renderings.

5 Aug, 2011 ASRockus
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
The V-Ray Adv 1.5 RC5 also have something like Show Last VFB button in the tab V-Ray Frame Buffer., But you can view the latest Render (like so).

13 Feb, 2011 RenderStuff (Staff Author)
6 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
No, actually, Show Last VFB, only allows you to call accidentally closed window frame buffer with the last renderer in it at the time, as the VFB History (history buffer Frem) - allows you to compare two different rendering. In any case, this topic has been much discussion has gone beyond the Irradiance Map and walked toward the frame buffer 🙂 According to this, if you want to talk to any other CG topic other than just the theme of the discussion (IM), please open a new discussion and there we will continue our conversation😉

30 Aug, 2011 Fco3d
30 Aug, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Excellent explanation I been looking for something like this long time, congrats very helpful.

13 Feb, 2011 RenderStuff (Staff Author)
15 Sep, 2011 # Re: Irradiance Map VRay 1.5 tutorial
Thank you for your interest! You can follow the next tutorials, they describe the every aspect of optimal V-Ray setup.

19 Nov, 2011 oumhani
19 Nov, 2011 # Re: Irradiance Map VRay 1.5 tutorial
great tutorial on a not so easy to understand concept, thank you

21 Feb, 2012 Peps
21 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Hello! There was a problem. I have a scene with your render settings I changed in Irridiance map min rate -6, max rate -1. 6. Total number of prepassov render 1500H1000 - 4-5 hours, quality suit. I did another scene, and tried to pour it in the first through Marj (previously wiped her) tried to upload settings render the first stage through the load presets to make the rendering for the second, but then bummer - the number prepasov was 7 and render time go to infinity. What is the reason? HELP!

21 Feb, 2012 Anton (Staff Author)
21 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Hey, the reason for the material used for the interpolation Glossy effects of the Irradiance the Map , that is one of the materials activated the Use interpolation . In addition, if one of the materials used scenes Raytrace map, it can also be the cause of care rendering V-Ray to infinity .

21 Feb, 2012 Peps
21 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Thank you so much! I read all about the problems of rendering Vray, and realized that my future still need a good library with materials specifically for Vray. Want to cook, do not self-learned and taking into account the specifics of my work is not necessary. Recommend these libraries please.

21 Feb, 2012 Anton (Staff Author)
21 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial

21 Feb, 2012 Peps
21 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial
A low bow to you! 👌

22 Feb, 2012 Ant
22 Feb, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Great tutorials but you were very quick to discard Brute Force as a GI option,,,

When used in the right hands, and with enough experience and understanding of Vray's render settings, Brute Force provides superior GI calculations resulting in highest quality and whilst you are correct that it can be time consuming, I feel that this may put beginners off and could prevent them from ever achieving Vray's ultimate results.

Aside from that comment, your tutorials have been very informative and the CG community is a better place for having this information 😉

15 Mar, 2012 cybreous
15 Mar, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Im failuring everytime when i do this, im saving the maps and doing the tutorial step by step, it all works fine with the precalc, but when i do the final render it stucks and renders the first frame over and over again, it never moves forward,please can anyone help me to get this working right, don't know what iam doing wrong

22 Mar, 2012 Delgado
22 Mar, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Great tutorials, I'm new to v-ray and these are by far the best tutorials i have seen regarding initial v-ray set ups


20 Nov, 2012 MARCO
20 Nov, 2012 # Re: Irradiance Map VRay 1.5 tutorial
Why there may be bright light spots on the rendering and how to get rid of them? what about this topic? :| no info was given on the subject...

21 Nov, 2012 Maks (Staff Author)
21 Nov, 2012 # Re: Irradiance Map VRay 1.5 tutorial
MARCO, please attach a link to an image with these spots, so we can get a better idea about causes of their appearance on your rendering.

25 Jan, 2013 Ioan Alex
25 Jan, 2013 # Re: Irradiance Map VRay 1.5 tutorial
Thx for explaining all detailed options
great tutorial


28 Dec, 2013 phadron
28 Dec, 2013 # Re: Irradiance Map VRay 1.5 tutorial
Hi, this is a super tutorial! thank you for this. I have a question. 🙄 what is the right balance between an image full of points (samples) and one with less samples? when I have to stop with change IM parameters? is there a rule for this? this is a good IM map? -->

21 Nov, 2012 Maks (Staff Author)
29 Dec, 2013 # Re: Irradiance Map VRay 1.5 tutorial
Right points balance in theory is when there are lot of points on the small details giving more quality, and few points on flat regular planes letting one to lower the rendering time.

On practice, though, we do not advice to look on IM map unless you have some mysterious artifacts; IM map may help to resolve such problems. You rather look on the rendering results and tune the parameters based on the final color output. The only criterion of the good render is when the render looks good, not when it is theoretically correct or balanced.

14 Jun, 2014 Olivié C
14 Jun, 2014 # Re: Irradiance Map VRay 1.5 tutorial
Thank you for this great tutorial.

2 notes :

> your explanation of "Interp. Samples" is not in line with the V-Ray online manual : it's not about the "quality" of the interpolation but rather about the "quantity" (number of IM samples interpolated).
You say "Default value of 20 samples is enough, and this value should not be changed." well you actually need to increase this when you use high IM quality (say Max rate = 0) in order to avoid artefacts (since you need to interpolate more samples to smooth the highly sampled GI). Increasing "Interp. Samples" can actually be necessary in such cases for interior rendering.

> "Min rate -5 and Max rate -3 is sufficient for the good photo-realistic rendering" well this sounds a bit optimistic and a good advice for preview, but it's still ok to render the final image with Max rate -1, or 0 if usefull.

Thanks again for your tutorial !

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