Thursday, June 14, 2012

Vray Materials by VIS CORBEL

To begin creating beautiful materials, we must first understand how the VRay material works. Let’s take a closer look at the VRayMtl, VRayFastSSS2, and VRayBlendMtl. These 3 are the main material types that are essential for realistic results, you can achieve almost anything with them. VRay offers even more material types, but those are meant for pretty specific tasks and will not be covered in this guide.
Forget about using MAX Standard materials, they will give you slow, noisy and non-realistic results. VRay is designed to be used with it’s native shaders, so that is what we are going to do.
Let’s get started.
(You can click on the images to enlarge them.)
VRayMtl is the basic, most used, universal material that VRay offers. You will find that most of the materials you wish to create can be made from a VRayMtl.
This how the basic, unchanged material looks.

Now let’s look at the first section – Diffuse.

Think of Diffuse as the base color of the object. If you see a tomato, you can instantly tell it’s red. This means that red is the Diffuse color. It is a bit more complicated for very reflective or very refractive objects, but we will look at those later.
VRayMtl allows you to choose a simple color as the Diffuse or use a Map. You can use any Bitmap or Procedural Map in the Map slot.
Here is an example.

The Roughness parameter can “flatten” the color transitions. You can use it to make your material appear dusty and flat. Here is an example with the same green material at 0, 0.5 and 1.0 Roughness.

Next section is Reflection

As the name suggests, this section deals with the reflective properties of the material. Most real world objects are reflective. Look at these photos of chrome and brick for example.

The reflections of the chrome are very strong and sharp, you can instantly recognize it as a reflective surface. But what about the brick? It might look that it’s not reflective at all, but in fact the reflections are just weak and very very blurred. The only objects that don’t reflect any light are the black holes :) Keep this in mind when creating the materials.
Let’s look at the parameters now.
First is the Reflection color.

Black color makes the material non-reflective, white color makes it fully reflective. All the gray scale values between increase or decrease the reflection strength. The color sliders in 3Ds Max go from 0 to 255, this means that if you want to make a material that reflects 50% of the light that hits it, you need to set the value of the reflections to 128. Here is an example at 0, 128 and 255. Notice how the third image has lost all the Diffuse color and is only showing the reflections. Reflections make the base color weaker as they get stronger. The Energy Preservation law doesn’t allow realistic materials to reflect more light than they receive. This means that If the material has 0% reflections, it shows 100% of the Diffuse color. If the material has 30% reflections, the Diffuse color is weakened to just 70%, and so on. Think of the reflections as a layer on top of the Diffuse, together they create the final image.

Just like with the Diffuse, you can use Color, Bitmap or Procedural map in the Reflect slot. Here is an example with all three.

The Diffuse color for all the examples is 128 gray. Notice how the Reflect color changes the look of the Diffuse. This color change happens because VRay adheres to the Energy Preservation rule. If the material reflects the red colored light, the red color is subtracted from the Diffuse and only green and blue are left. This behavior can sometimes make it difficult to predict the final result, this is why you can change the Energy Preservation mode in the material options. If you choose Monochrome, only the reflections will be colored and the Diffuse color will be left unchanged.

Next up is Reflection Glossiness. This is the parameter that controls how sharp/blurred are the reflections. Some real world objects, like polished metal, mirror, chrome, have very sharp reflections, while other materials, such as wood, concrete, plastic, etc., have blurred reflections. You can adjust the Reflection glossiness from 0 to 1 (completely blurred to perfectly sharp). For most materials you will not need to lower the glossiness below 0.3. You should always use blurred reflections with caution, do not lower the glossiness more than necessary, as this will cause more noise in your image, you can get rid of it by increasing the Subdivs, but it will take a toll on the rendertime. Here are some basic examples of how the glossiness works.

Notice the noise introduced into the image. You can clean it up with the Subdivs parameter, increasing it will make reflections smoother at the cost of render time. Notice how the render time has increased 3.5 times if you compare the third and first images. 16 is a good choice for decent result without too much waiting. You can use the subdivs parameter to find a balance between time and quality.

I do not recommend unlocking Highlight glossiness and changing it, if your goal is realistic materials. This parameter allows you to ‘fake’ the blurred reflections without actually calculating them. It can sometimes be used for quicker renders if deadlines are tight.
Next up is the Fresnel parameter. You might have heard that all real world materials feature Fresnel reflections, but what does it actually mean? Fresnel changes the reflection strength depending on the viewing angle. General rule is that reflections are weaker if the surface is facing you perpendicularly and increase in strength as the surface approaches parallel position relative to your viewing angle. Here are some real world examples where you can see this effect in action. The marble, car and wall surfaces are much more reflective when they are more parallel to the viewing angle.

And here is how the Fresnel IOR or Index of Refraction works. Use only values from 1.01 up, lower values are not physically correct for normal materials. Increasing the IOR changes the relationship between the angle of the surface and reflection strength, look at the examples.

As a general guideline, here are the Reflect IOR values for some common object types:
water 1.33
plastic 1.45
glass 1.5-1.8
diamond 2.4
compound materials like wood, stone, concrete etc 3-6
metals 20-100
Exact values need to be fine tuned for each material to achieve the right look.
Next parameter is Reflection Depth. This is the number of times a light ray is reflected before stopping the calculations. When the set number of reflections has been calculated, the rest are simply displayed as the Exit color. You can try setting a bright color as the Exit color to see how much information you lose. Look at the example, the green parts show the areas which would benefit from a larger number of reflections. As you can see, 6 reflections are plenty for this scene. Other scenes with more reflective surfaces might need a larger value.

Let’s move on to the next section – Refractions
These settings control if and how the material let’s the light through it. Common materials that have refractive properties are glass, water, gems, transparent plastics, etc.
First parameter that controls the refractions is Refract color. As before, it goes from black (no refractions) to white (full refractions) and everything in between is a mix between Diffuse and Refraction.
Here are some examples with a black material. I recommend using black diffuse color [1;1;1] for most of the transparent materials and adjust the overall color with Refract color and Fog color.

You can use a color, bitmap or procedural map in this slot as well.

Refraction glossiness. Just like with the reflections, you can change how blurry are the refractions. This effect is great for frosted glass or any other rough surface that lets through the light but distorts it along the way.
This one increases render times and noise a lot so be careful with it. No need to go lower than 0.6 for most materials.

To clean up the noise, we need to increase Subdivs parameter. As you can see, getting a clean result comes with a huge cost. The render time for the last image is almost 7 times longer than with the default value. It is also 15 times longer than not using blurred refractions at all! So try to minimize the blurred refractions if you need fast renders.

In the real world light changes it’s angle as it travels between objects of different density, thus the surface ‘refracts’ the light. IOR value of 1 let’s the light through without bending it, as the IOR value increases, so does the angle at which light is refracted. Look at these examples.

Index of Refraction has been calculated for many materials, so you don’t need to guess. You can find various IOR tables on the internet. Here is one of them:
Acetone 1.36
Actinolite 1.618
Agalmatoite 1.550
Agate 1.544
Agate, Moss 1.540
Air 1.0002926
Alcohol 1.329
Amber 1.546
Amethyst 1.544
Crystal 2.00
Diamond 2.417
Emerald 1.576
Ethanol 1.36
Ethyl Alcohol 1.36
Glass 1.51714
Glass, Albite 1.4890
Glass, Crown 1.520
Glass, Crown, Zinc 1.517
Glass, Flint, Dense 1.66
Glass, Flint, Heaviest 1.89
Glass, Flint, Heavy 1.65548
Glass, Flint, Lanthanum 1.80
Glass, Flint, Light 1.58038
Glass, Flint, Medium 1.62725
Gold 0.47
Ice 1.309
Ivory 1.540
Jade, Nephrite 1.610
Jadeite 1.665
Lead 2.01
Malachite 1.655
Methanol 1.329
Moonstone, Albite 1.535
Nylon 1.53
Onyx 1.486
Opal 1.450
Oxygen (gas) 1.000276
Oxygen (liq) 1.221
Pearl 1.530
Plastic 1.460
Plexiglas 1.50
Polystyrene 1.55
Quartz 1.544
Quartz, Fused 1.45843
Rock Salt 1.544
Rubber, Natural 1.5191
Ruby 1.760
Sapphire 1.760
Silicon 4.24
Steel 2.50
Tiger eye 1.544
Topaz 1.620
Tourmaline 1.624
Turpentine 1.472
Turquoise 1.610
Water (gas) 1.000261
Water 35′C (Room temp) 1.33157
Zirconia, Cubic 2.170
Max depth works just like with the reflections. The default value is usually fine, but for scenes with large amount of refractions, you should increase it.
Next parameter is Fog Color. It is great if you want to tint the glass in a realistic way. Using the Fog color makes thinner parts lighter and thicker parts darker. You can use the Fog multiplier value to adjust how strong is the tint. I suggest using colors with less than 255 lightness and saturation for realistic results.

You can control the relationship between object thickness and Fog intensity by using the Fog Bias value. Look at the examples to see how it works. Negative values make the tinting stronger and color transitions more extreme, while positive values make the fog smoother and weaker. Use it together with fog multiplier to get the effect you need.

The biggest drawback of the Fog color is that you can not use a map in this slot, this means you can only use a single color. If you want to create a stained glass material or glass with multiple colors, you will have to do that by using the Refract color and not the Fog. It is, however, great for those single-colored materials and much more realistic than simply changing the Refract color.
VRay 2.0 introduced the long awaited Dispersion feature for refractive materials, until 2.0 you had to use a ‘fake’ method of blending multiple materials with different Refract colors and IOR. Now you can simple activate the Dispersion and change the strength with Abbe number. Smaller values makes the dispersions stronger, while larger numbers makes them more subtle. Use your own artistic eye to figure out how much dispersions you need. You will have to increase the Refract Subdivs for a nice result (with the default value materials have a green tint), even if you are not using glossy refractions. Dispersion also increases the render time.

Next section is Translucency, but we are going to skip it, as I prefer to use VRayFastSSS2 material for translucent objects. It offers much greater speed and flexibility.
Let’s look at the BRDF section.

First is the BRDF model. This parameter affects how the specular highlights of the material are calculated. VRay offers 3 options: Phong, Blinn and Ward. Phong has the sharpest highlights, Blinn is a bit more blurred and Ward is even softer. Blinn is the default value and it is fine for most materials, for metals you will want to use the Ward model.

Anisotropy allows you to create stretched highlights. In real world these are most commonly seen on brushed metal surfaces with long, parallel ‘scratches’. Anisotropy allows you to fake this by stretching and rotating the highlights as you like.
This example shows how changing the Anisotropy value changes the speculars. Negative values stretch them highlights horizontally while positive values stretch them vertically.

You can also change the angle manually to any value you need. Here is an example with stretching rotated at 45 degrees.

And finally you can change the reference axis for even more control.

Next comes the Maps section of the material. This is a convenient list of all the slots you can assign bitmaps or procedural maps to.

There are some important properties of the material that can only be accessed through this section. These are Bump, Displace and Opacity.
Let’s look at the Bump and Displace slots first.
Both of these slots allow you to assign a bitmap or procedural map to simulate unevenness and deformation of the objects surface. Bump does so without changing the overall geometry of the object, but Displace actually subdivides and deforms the object during rendering. The deformations work like this – middle grey [128;128;128] of the map does not change anything on the object, darker values push the surface inwards while lighter values pull it out. The further this value is from medium gray, the stronger is the effect. Color of the map is not taken into account and only the lightness value is used.
Bump is fast and Displace is slow.
If you need large, realistic deformations, you should use displacement, while bump is perfect for smaller things that don’t change the objects outline. Look at the examples to see the difference.

Last map we are going to look at is the Opacity map. It works very simple. Pure white value is used for the non-transparent parts of the material and pure black is for completely invisible parts of the material, everything in between is more or less half transparent. It is great if you need to simulate stuff like tree leaves or lace fabric without using a large amount of polygons. Here is an example using the same map as in the Bump samples.

The two next segments of VRayMtl are Reflect Interpolation and Refract Interpolation. They are supposed to be a quicker way for calculating blurred reflections and refractions, but I will not be covering those, as I have often found troubleshooting the issues/glitches that can appear from them take longer time than rendering non-interpolated materials.
This wraps up the basic VRayMtl, it already allows you to create 90% of the materials you will encounter in your work. There are, however, some special cases where other materials are better suited.
Let’s look at the VRayBlendMtl. It is the perfect tool for making compound materials.For example, if you need to create a black, shiny surface with blurred gold spots, it is way easier to create two materials and blend them together than hand painting all the different maps you would need to achieve this effect in a single VRayMtl.
The VRayBlendMtl works with a layer-like system.
There is a Base material to which you can apply multiple Coat materials. You can control how much of the coat material is applied by using Blend Amount color, Bitmap or Procedural map. Pure white blend color shows only the coat material, medium gray shows 50% of the coat material and 50% of the base material and finally pure black doesn’t show any coat material at all.

Here is the same blend material with black and white checker map in the Blend Amount slot.

Each next coat layer treats everything above it as a single material, if you have a base material and 2 coat materials at 50%, the result is 0.5(0.5base+0.5_1st_coat)+0.5_2nd_coat.
In this example I’ve added a second coat layer with pure green diffuse color, if all 3 parts would be used equally, the resulting color should be white (RGB at equal values result in grayscale color), but it is instead a 50/50 mix of purple and green.

You can use up to 10 material in a blend (if you then create a new VRayBlendMtl and keep the filled one as sub-material, you can add 9 more materials, repeating this procedure gives you unlimited amount of slots). Here is a somewhat more complex example of a 4 material blend.

I am sure you now see the potential of VRayBlendMtl. I will show you some practical examples on how to use it in the videos.
Let’s move on to the next material type – VRayFastSSS2. The letters SSS stand for Sub-Surface Scattering, another common name is Translucency. This effect happens when light rays don’t go straight through the object, but are scattered in multiple directions when inside, this does not allow you to see through the object, but you can see the light inside it. Unlike refraction glossiness which scatters light rays at the surface, SSS does this inside the object. This makes some interesting lighting effects, the light penetrates the object and lights it from within. Some real world examples are: flesh, milk, marble, jade, fruit, wax etc. Look at these photos to see what I’m talking about.

VRayfastSSS2 is perfect for this type of materials.
My example scene for this section has just one light behind he object to illustrate the sss effects better.
Compare the VRaymtl and VRayfastSSS2. Notice how the regular material doesn’t let any light in, only bounces it off the surface while VRayfastSSS2 is more illuminated. The effect is very subtle though.

The easiest way to increase the translucency effect, is by increasing the Scale setting. The larger the Scale, the deeper light goes into the object.

Next parameter, SSS prepass, controls the accuracy of the scattered light. Lower values give blurrier results, while higher values give a more precise rendering, the precision comes with an increased render time. For production renders, I suggest using values of -1 to 1.

Fast SSS allows you to set the IOR as well. Most water based materials like skin, milk, juice, plants have IOR of ~1.3, for stone type materials 1.5-1.7 is more suitable.
You can also use the built-in presets to quickly create some common materials, these are:
Skin (brown)
Skin (pink)
Skin (yellow)
Milk (skimmed)
Milk (whole)
Marble (white)
Water (clear)
If none of the presets fits, you can create the material yourself.
Let’s look at the settings.
First is the Overall color. This color allows you to change the color of the whole material (the surface and the inside).
Look at the examples to see how this color changes the look of the default VRayfastSSS2 material.

Next is the Diffuse color and Sub-Surface color. First one controls the outer surface, second one controls the inside of the object. This works somewhat different than VRaymtl. By default, VRayfastSSS2 only uses the sub-surface color and scatter color as the main sources of pigment. You can assign a diffuse color and increase the diffuse amount to mix it with those two colors. It is a bit hard to explain, I’ll show you an example. Here I have assigned a Red Diffuse color and a Blue sub-surface color. With the default setting of 0 Diffuse is not seen at all, when I increase it to 0.5 it is a 50% mix with the blue and finally, when I set it at 1, there is no more translucency and only the red diffuse color is seen.

Ok, let’s look at the Scatter color now. The lightness of this color affects how strong is the scattering effect. It get’s stronger from black to white, as usual.
I’m using a simple grey material with red sub-surface color in this example.

You can also use a saturated color in this slot to give a tint to the object. It work’s best if you use a color that is close to the sub-surface color. It also tints in the opposite direction, sounds weird, I know. What it means is if your sub-surface color is red and you set the scatter color as orange, the actual tint will be to the opposite direction of the hue scale – purple. If you use purple, the tint will be orange. Look at the pictures to see it in action. The effect is subtle, but sometimes it’s just what is needed!

Scatter Radius works just like Scale, you can increase the depth of translucency by increasing this value.
Let’s look at the Specular Layer now.
You can make the VRayfastSSS2 material reflective by enabling Trace Reflections option. You can control the look of the highlights just like with the VRaymtl – by changing the glossiness value.
All these settings – glossiness, subdivs, reflection depth work just like in the basic VRaymtl.

Let’s move on to the Options section.
The main setting here you need to focus your attention is Single Scatter mode.
There are 3 possibilities you should use depending on the material you are trying to create.
Simple mode is best for materials where the light doesn’t go too deep, best examples are skin, plastic.
Refractive mode is great for materials that are very translucent but at the same time quite opaque (marble, milk)
Refractive (raytraced) mode is for more transparent materials, this also creates nice refractions and transparent shadows. Use it for materials like glass, water, crystals.

For the best results, turn Front lighting, Back lighting and Scatter GI on.

Tuesday, May 8, 2012

Vray speed tips for 3d visualisation

Here is a compiled list of tips that can improve Vray rendering speeds whilst maintaining a high level of quality. These tips come from my own experience, they may help improve your rendering, but they are not to be used as a definitive solution as every 3d project is different. I have categorised each tip to make it easier to follow and although some may seem obvious, I thought they should be mentioned as they can be useful.

Global switches

  • When working with 3rd party CAD data, specifically Autodesk Inventor 3d files imported into Autodesk 3ds Max, leaving displacement ticked increases render times considerably. I assume this is to do with how it reads the mesh data. Obviously you will need to leave this on if you plan to have displacement in your scene, if not, turn it off.

Indirect illumination (GI)

Irradiance map
  • This GI method is resolution dependant, so adjust the min/max rate to suit your output resolution.
  • If you have multiple camera views for the same scene, save out an incremental irradiance map. The same map can be used providing there is over lapping geometry between camera views. This will save you some rendering time.
  • Tick show calc. phase, this will show you the irradiance map as its calculating. After a few seconds you will begin to get an idea of the general illumination of the scene. If it is incorrect you can cancel the render, therefore only wasting a small amount of time.
Light cache
  • Tick use light cache for glossy rays, this can reduce rendering times by quite a lot if you have heavy glossy reflections in your scene. Keep in mind that it is very dependent on the scene and because of this, in some instances it can lead to unwanted artefacts. There are multiple steps you can take to avoid this happening.
Option A
If you have the latest version of Vray (which is 2.0), there is an added feature called retrace threshold which improves the precision of the global illumination and helps eliminate light leaks when use light cache for when glossy rays is on.
Option B
Set the filter to fixed and adjust the filter size to two or three times the sample size. So if your sample size is 150 mm set the filter size to 300 mm.
Option C
Within a material, scroll down to the options panel and set treat glossy rays as GI to always. Also turn off the use light cache for glossy rays if you have it on. By doing this you are telling the material to always use the secondary GI engine to calculate the glossy rays, which in this case is the light cache. It basically does the same job as use light cache for glossy rays but you can specify which materials within the scene use this option.
  • Use screen as a method for scale when dealing with scenes that have large ground planes and distant objects. If you choose world scale, you may find that these distant objects can become very noisy, and you may decide to increase samples to remove this noise which will lead to longer render times.
  • Set your number of passes to the number of processor cores you have in your PC. Even if you have multiple cores over multiple PC’s, the light cache is only calculated on one PC.

System settings

  • By default, Vray sets the dynamic memory limit to 400, but this can actually go a lot higher. It is recommended to change this to a value that is half your RAM amount. For example if you have 8GB of RAM, you can set this to 4000.


Image output size
  • It is important to understand render output resolution and DPI, Make sure you know what’s happening to the render once you have signed it off. If you have rendered an A3 image at 300 DPI and you then later on find out that image was going into a small area on an A5 leaflet, you have rendered your image at a higher resolution than what was required.

Render elements

  • Save out all your passes as separate files to later on composite them in post. This will allow you to tweak each individual aspect of your render such as lighting, reflection, refraction and shadow without the need to re–render the whole image again.

Image sampler

Antialiasing filter
  • Sharpening filters such as Mitchell-Netravali and Catmull-Rom may increase noise within the render, to compensate more samples are required to reduce the noise level. Turn the filter off completely and add it in post. Renders of around 3000 pixels are fine without a filter. Only use a filter when rendering smaller images to avoid antialiasing issues

  • Adaptive subdivision is best used for flat non reflective materials such as buildings, whereas adaptive DMC is better and faster for glossy materials and camera blur.

Material editor

  • When adjusting the reflective glossiness, you will need to increase the subdivs value to compensate, otherwise you will get very noisy results. Do not fall into the habit of setting the subdivs to a value you use throughout your scenes. Setting all your reflective materials to a subdivision of 32 for example, is not a solution. In fact it will increase your render times unnecessarily. Keep in mind that the higher the reflective glossiness, the lower subdivisions you can have. If you have reflective glossiness set to 0.85 you can set your subdivisions to 16 or even lower depending on your set up. If the reflective glossiness is set to 0.6, it would require a higher subdivision. This requires a little experimenting but it is good practice, especially for architectural visualisation, to have a default library of materials that you can use for multiple projects. This way, you won’t have to keep adjusting subdivisions because you know that material from your library is good enough.
  • From experience, adjusting the refraction glossiness does more harm than good unless you are aiming for a frosted effect. If not the majority of results are less than noticeable, and the render times are through the roof. Keep this at 1.0. You will save so much render time this way.
Vray materials
  • Vray calculates its own materials faster than non Vray materials because they are specifically optimised for Vray. A scene can easily be converted by right clicking the viewport and using the Vray scene convertor.


Gamma and LUT
  • Without gamma correction, you are forced to add extra Vray lights in darker areas to further illuminate a scene causing the render times to go up. Gamma correction gives more luminance therefore fewer lights are needed. Within the 3ds Max preferences, enable gamma and set it to 2.2 and tick affect colour selectors and material editor. You will also need to change the Vray gamma. In the render setup under colour mapping set the gamma to 2.2.

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Compositing Vray render elements

The purpose of rendering out multiple passes is that it allows you to tweak all aspects of an image such as global illumination, direct light, diffuse, reflection, specular etc. These passes can then be compiled together in Adobe Photoshop.
The whole process of saving out the different render passes may seem like an extra task within your workflow but it will save you a lot of time, especially if you wish to reduce the reflection of a material or change the colour of an object. Without render passes you would result in rendering the image again and that is not the best way to go if you have a deadline looming.
Vray has multiple render elements, some are compulsory where as others are not. To view a list of render elements that Vray supports click here. Before I start, I would like to point out that I will be using a linear workflow with a gamma 2.2 setup within 3ds Max and Vray. I strongly recommend setting this up as it will improve many areas within your workflow. You can find an easy to follow step by step guide here.

Selecting the render elements

Within the Vray render settings go to the render elements tab and add the following elements.
The difference between VrayRawGlobalIllumination and VrayGlobalIllumination is that the raw version is not multiplied by the diffuse colour. This allows much more control in post processing
The pure diffuse surface colour, combined with VrayRawGlobalIllumination it will give you VrayGlobalIllumination.
This element works in the same way as the VrayRawGlobalIllumination. Combined with the VrayDiffuseFilter the result will be VrayLighting
The reflections on the surface.
The surface specular highlights.
As long as you have given all your materials within your scene a material ID, the resulting render element will be a mix of solid colours that correspond to a material ID. This can then be used to colour pick areas within your render to adjust in post.

Providing you are using the Vray frame buffer leave all settings as they are. There are other render elements that are not included in this guide that you may need depending on the type of project, such as VrayZDepth for DOF, VrayRefraction to control the opacity and VrayExtraTex combined with Vray Dirt to create an ambient occlusion pass.
Additionally you can add the VrayRawShadow element to control the intensity of shadows but from experience, the outcome is sometimes less than desired because of the low amount of samples it uses to calculate. Similar to the diffuse pass, the end result is not very smooth. It’s best left combined with the GI and lighting elements.
Vray render elements also work best with Vray materials, if some of your objects are standard materials they may not function correctly as a render element. So double check that your objects have Vray materials applied before you render.

Auto save the render elements

Because there are many passes saving these out one by one is time consuming and out of the question when you are creating an animation. In the Vray frame buffer rollout tick split render channels and choose a location to save the render passes. I recommend saving as a TIF file with at least 16 bit Colour. This will allow for maximum range when adjusting the levels in Adobe Photoshop.
Leave save RGB and save alpha ticked. The RGB will be the completed render which combines all the render elements before any post production, this is known as the beauty pass. Due to the fact that you are saving the resulting image here, you do not need to specify a location for the render output in the common tab. Ignore the pop up warning for no files saved.
At this stage it is important to note that if you are following the gamma 2.2 and linear workflow setup mentioned earlier the rendered image will appear darker in the Vray frame buffer because don’t affect colours (adaptation only) is ticked. To see the actual result click the sRGB button in the Vray frame buffer during or after rendering.

Compositing the render elements in Adobe Photoshop

In Adobe Photoshop go file/scripts/load files into stack. Then select all the render elements and click ok, this will add all the elements into a single work file for you. Then re-order the stack into the following:
  • Alpha
  • RGB Colour
  • VrayMtlID
  • VraySpecular
  • VrayReflection
  • VrayRawLighting
  • VrayRawGlobalIllumination
  • VrayDiffuseFilter
The VrayDiffuseFilter will be used more than once and is combined with other render elements. A main purpose for the diffuse pass is to easily apply colour correction and if necessary, change the colour of an object completely. So that you do not have to manually adjust each diffuse pass, convert it to a smart object by right clicking the layer and choosing convert to smart object. Now duplicate the newly created smart object and place it under the VrayRawLighting so that both main light sources now have a diffuse layer to blend with.
To edit the smart object at any time, double click the layer and it will open in a new window. Once completed save and close and it will automatically update the smart object and any duplicates within your composition.
Set the VrayRawGlobalIllumination blend mode to multiply and create a clipping mask so that the blending of the VrayRawGlobalIllumination only affects the layer it has been clipped with. To do this hold down the Alt key and click between the VrayDiffuseFilter and VrayRawGlobalIllumination (The cursor will change into two circles). Repeat this step for the VrayDiffuseFiltercopy and the VrayRawLighting elements.

Group both the VrayRawLighting and VrayDiffuseFilter. Do the same for the VrayRawGlobalIllumination and VrayDiffuseFilter. Then change the blend mode between the two groups to linear dodge (add).
Linear dodge (add) adds the colour information from the blended layer and removes the black because it is seen as a value of 0 and is therefore invisible. A basic terminology is anything that adds light is to be linear multiplied such as GI complete with diffuse, reflection, specular etc.. Anything that takes away light (such as shadows) is to be multiplied.
Turn on the VrayReflection and VraySpecular layers and set both of their blend modes to Linear dodge (add).

Gamma correction

At the start I mentioned that the composition will appear darker than normal. This is because we are still working in linear space. Add a levels adjustment layer on top of the stack and change the middle Input slider to 2.2. The middle input slider adjusts the gamma in the image. For more information on level adjustments click here.
Some gamma users have mentioned that the results can appear washed out. To correct this you can add further adjustment layers to improve the colour and contrast.

This has been a summary of the required render elements to complete an RGB beauty pass. There are many more elements and adjustments that can be added to aid with post processing. However, it is very much down to the type of project and the result you are after.

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