Introduction

While the Glossiness map describes surface detail on a microscopic level, Bump and Normal maps are mostly used for details visible to the naked eye. Both maps are light effects and don't affect geometry - they render highlights and shadows to fool the eye. This is faster to render than geometric detail and is easier to adjust, however it has its cons. Both Bump and Normal maps are quite unsuitable for large scale details (especially for large protrusions) and don't affect the shape of objects silhouette. In scenarios where such details need to be produced, a Displacement map needs to be used.  

Bump Map

Bump maps simulate relief using greyscale values. White pushes out/up, while black pushes in/down. Both textures and procedural 3ds Max maps can be used. Because of the greyscale nature of these maps, textures can be created easily directly in 3ds Max or in Photoshop. They can also be derived, for example, from a Diffuse map. A better way to generate Bump maps is to use a dedicated texturing software like Substance Designer, Substance Bitmap2material, PixPlant, etc. These programs can be fed with a Diffuse map that has lighting information embedded and with a few tweaks output a Bump texture (along with other texture maps).

Bump maps are usually directly plugged into the Bump map slot of a V-Ray material. Bump strength defaults at 30 and acts as a multiplier where 30 means 30% power. Negative values invert the bump. This parameter is something quite unintuitive to work with. There are no certain rules, we have to experiment to get correct results (it's nice to have a VRayBumpNormals pass when experimenting with bump so you can really see what you're doing). This is one of the major drawbacks of a Bump map vs. a Normal map where the strength has a default value which produces correct results for all maps. More on this a bit later.

Bump maps are data maps so they should be loaded, when available, with Gamma 1.0 (VRayHDRI: Iverse Gamma: 1.0).

VRayColor2Bump Map

V-Ray has a nice map that can work a bit more intuitively with Bump maps. It's called VRayColor2Bump and it uses real-world units, centimeters, to control the depth of the bump. A value of 1cm for this map means that the difference between white and black in the map is 1cm and the luminance is set to mid-grey. In other words Black=-0.5cm, Mid-grey=0cm, White=0.5cm. Textures that do not have completely white or black values simply won't reach the maximum/minimum values (-0.5cm and 0.5cm). That's why, if you want to reach exact values in your bump, you need to have completely white and black values.

VRayColor2Bump can use a simple Bump texture or a whole map network as a base. As the Chaosgroup documentation on this map suggests, it takes more resources to render as opposed to directly plugging a Bump map into the bump slot. Therefore it needs to be used wisely. As a general rule - if you have a Bump texture that has no colour corrections made in 3ds Max, plug it directly into the bump slot and find the appropriate value. If you have colour corrected the Bump map in any way (this includes colour correction, output, composite, mix, etc. map), then plug it into a VRayColor2Bump map and then plug it into the bump slot. Remember to change the default multiplier of the bump slot from 30 (or whatever number you've had before) to 100, which means that the map that has been plugged in will have 100% power.

Normal Map

Normal maps are colour maps. They use the Red, Green and Blue channels to represent the X, Y and Z axis in 3D space. This means that Normal maps as opposed to Bump maps "deform" the surface in all 3 axes instead of only Z (up and down) and give better results. Normal maps are very hard to be hand painted in softwares like Photoshop (an exception here is Mari which allows for painting Normal maps). When we are talking about materials, Normal maps are usually created by using the lighting information of a Diffuse map. Scanned surfaces are always the best option and give true to reality results, while photographed surfaces will give only an approximation - all based on software possibilities and tweaking. Programs that can create Normal maps are Substance Designer, Bitmap2Material, Knald, PixPlant, xTex to name a few. Another way to produce a Normal map is baking it from a high resolution version of a mesh on to a lower one.

In 99% of cases, Normal maps are exported in Linear color space. Even though they have colour, they are considered to be data maps as they are produced entirely by the computer. That's why we need to load them with Gamma 1.0 (VRayHDRI: Iverse Gamma: 1.0).

If you experience strange results with your Normal map, it might fall in the 1% category where something probably went wrong while exporting. You can see if your map needs Gamma correction or not if you open it up in Photoshop and sample a region of the map that seems "flat" with the picker. Look at the RGB values you get. If they are around 200,200,255 sRGB - then the map does not need Gamma override. If you get values around 128,128,255 sRGB then you need load the map with a Gamma override of 1.0. With time,  you will get used to the correct look of Normal maps in the Material Editor - these maps should look fairly bright so you will notice if the map looks darker than it should be (which would be the case if it's loaded with incorrect Gamma). 

Normal Map Types

There are two main types of Normal maps used in the industry - Tangent Space Normal maps and Object Space Normal maps. The first type is the one most commonly used and is composed manly of purple-blue colours. These maps deal very well with object deformations and are the ones we use. Object Space Normal maps have a rainbow colour assortment and are used in the industry mostly for objects that won't deform, however, even in such cases the Tangent Space Normal maps are used more often.

More importantly, there are two standards for outputting Normal maps - OpenGL and DirectX.

In a sense, OpenGL maps look "logical" and DirectX maps looks like they are "inside out". When you use maps downloaded from online resources, sometimes you won't be able to judge so easily as in the example above and you will have to do a test render. Bricks for example are a bit hard to judge when viewed at full resolution but if you actually zoom-out and look at them as thumbnails it becomes a bit more prominent if they are "logical" or "inside out".

Furthermore, sometimes (very rarely) maps might have their channels swapped in which case you will need to swap them back. Here are a few tips to check if map channels are correct: for OpenGL maps, when looking at the Red channel the surface should appear to be lit from the right; when looking at the Green channel, the surface should appear to be lit from above. For DirectX maps, when looking at the Red channel the surface should appear to be lit from the left; when looking at the Green channel, the surface should appear to be lit from above.

Finally, to convert OpenGL to DirectX or vise versa, you need to flip the Green channel (Y).

Normal Maps in VRay

When using VRay there are a few rules when using Normal maps:

• Normal maps should be loaded with Gamma 1.0 override

• Any blurring/filtering should be removed for sharpest/best results

• Normal maps are plugged into a VRayNormalMap before going into the Bump slot of the material

• VRay works with DirectX maps, if you have OpenGL map you need to flip the Green (Y). Most maps found online will be OpenGL so you will need to flip Y most of the times

• Bump multiplier of the Bump slot should be set to 100 for correct representation. Normal map intensity should be controlled (if needed) from the multiplier in the VRatNormalMap