NORMAL MAPS: PART II - BEYOND THE BASICS - page 1

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1 BEN CLOWARD - Character Animator NORMAL MAPS: PART II - BEYOND THE BASICS - page 1 Introduction After writing the first tutorial, I compiled a list of all of the extra information that I wanted to include on the "Tips and Tricks" page. The list ended up being so long that I decided to create a whole new tutorial. With this second normal mapping tutorial, I'm going to go a bit more in depth for each of the steps of the process of working with normal maps. While learning how to create and use normal maps myself, I've learned a lot of information for how to achieve better results both on my own through trial and error, and also through research on the web. With Part II I'm going to go beyond the nuts and bolts of creating and applying normal maps and get into the jucy tid bits that really make them work well. Note: If you haven't followed the steps in the first tutorial and/or created your own normal maps yet, I recommend that you do that first before proceeding with this tutorial. I lot of the tips presented here cover issues that you'll run into while working with your first normal maps, and they may not make as much sense to you until you've actually tried out the process. In order to make things a little more organized, I've divided this tutorial into four main sections covering the four main steps of normal mapping (so far I've only finished the first one. Come back soon for the other three sections.): Tips for Creating Models As covered in the previous tutorial, normal maps can require creating both a high poly model and a low poly model. This section covers information to keep in mind while creating these models that will help you achieve a better end result. Methods for Creating Normal Maps The previous tutorial covered two methods for creating normal maps: converting a bump map to a normal map, and using ATi's NormalMapper program. This section illustrates some additional (and better!) methods for creating normal maps. Tips for Editing Normal Maps This topic was not covered at all in the previous tutorial but needs to be addressed here since editing a normal map requires some special care and consideration. Tips for Applying and Using Normal Maps I presented one method for applying normal maps in the previous tutorial: Nvidia's Cg plug-in for 3DS Max and Maya. There are several other good methods that I'll explore in this section. One more thing before you jump in. As I said in the first tutorial, I'm an artist, not a programmer. I'm writing this tutorial to help artists better understand the process (which can be quite technical) so they can use it to make better art. I hope it's helpful to you. If you find some problems, know some more information that would be helpful to include, or just would like to give me some feedback, I'd love to hear from you. me! Now get going and make some cool stuff!

2 NORMAL MAPS: PART II - page 2: Tips for Creating Models Tips for Creating Models As I've discussed, the whole goal of normal mapping is to make a low poly model look like a high poly model. This is usually achieved by creating both a low poly model and a high poly model and then using the detail of the high poly model to create a normal map for the low poly model. So we've got two models involved. This page contains tips for creating both the high and low res models that will help you to achieve better final results. First, we'll discuss the order of creation for the models. Which Model Do I Create First? So if you have to create a low poly model and a high poly model, which one do you create first? The honest answer is, which ever one you want! Here are a couple of options: Create the High Poly Model First If you are used to creating high poly models for non-real-time rendering, you might want to create your high poly model first. Once you've created a beautiful model with lots of detail, make a copy of the model. This copy will become your low poly model - you just need to reduce the poly count. Most 3D programs come with a feature to simplify a model. In 3DS Max, the MultiRes modifier works pretty well. Just crank the poly count down to a number that fits in your budget. If the model is a character that needs to deform, be sure that you leave enough detail in the joint areas for realistic deformation. Create the Low Poly Model First A lot of artists in the game industry are more comfortable creating low poly models. If that's you, you'll probably want to create the low poly model first. This gives you very fine control over the low poly mesh. (Sometimes resing down a high poly model, like in the previous method, gives you a very messy mesh.) Once you've got a low poly model you're happy with, make a copy of it. This copy will become your high poly version. Just subdivide it several times. The Mesh Smooth modifier in 3DS Max works well for this. Now go in and add all the detail that you've always wanted to add but couldn't because of your polygon budget. There are other options, but this is probably enough to get you going. Once you get started you'll probably settle on a method that you're most comfortable with. Tips For Creating the Low Poly Model The low poly model is the version that will actually get used in the game. It needs to have a poly count that fits in your engine's budget. Creating a low poly model that uses a normal map is a little different from creating a regular model. Here are some tips for getting good results from your normal map: Only One Smoothing Group, No Hard Edges Up until now, smoothing groups (or hard edges) have been a good way to accentuate features of a low poly model and make the details more clear and readable. It used to be important to use smoothing groups carefully to create a good model. Throw all of that out the window. Smoothing groups are an enemy to normal maps. Your low poly model should have one smoothing group (no hard edges). Here's why:

3 This image illustrates the process of generating a normal map. For every pixel in the normal map, a ray is cast from the surface of the low poly model outward along the normal where the ray started. The high poly model surface normal is recorded at each ray intersection. (A more detailed explaination is available in my first normal mapping tutorial here.) If your model has a hard edge, all of the rays on the polygons that share that edge will be uniform (go in the same direction). This will leave a gap in the rays between the two polygons. No data from the high res model will be recorded in this gap and an ugly seam on your final model will result. This image illustrates the same case but with a soft edge. Here we see that with a soft edge, the low poly normals are interpolated (smoothed) from one polygon to the other. There is no gap in the rays that are cast from the low poly model to the high poly model. No high poly model data is left out. There is a similar principle with regards to the high poly model. Be sure to check it out below in the high poly model tips section. Avoid Extremely Sharp Angles Because you're using one smoothing group, as mentioned above, if your model has sharp angles (greater than 90 degrees or so) you will get bad artifacts in your normal map. These are caused by the large difference between the angle of the faces and the vert normals. Round off your sharp angles with extra faces for better results, or if you need sharp angles, go ahead and use smoothing groups/hard egdes to create them. Hide UV Seams Well The low poly model needs to have UV coordinates applied. You should already be familiar with this process. There are a few things to keep in mind when laying out the UVs. The first is to hide your UV seams as best you can. Put them on the insides of arms, in the back of the head, where the neck meets the shirt, around the waist, etc. Try to find spots on the model were a seam makes sense. UV seams are much more pronounced in a normal map than they are on a regular diffuse texture. There is one method that you can use to erase them. I discuss that on page 4. Flipped UVs Issue In order to save space on the texture map and to achieve a high texel density, most character modelers will unwrap half of the model and then mirror that half for the other side. You can also do this during the unwrap process by selecting a group of UVs and flipping them horizontally or vertically and then laying them down on top of the coresponding set of UVs from the other side of the model. This is a great technique, but it causes some problems when creating normal maps. Here's the issue: The lighting on a normal mapped model is dependant on the surface direction (normal) of the polygons, but also on the normal direction of the UVs. It's as if the UVs have a normal also. When you flip the UV coordinates horizontally or vertically, the effect on the lighting is the same as if you flipped the polygon from front facing to back facing. Suddenly, the lighting looks like it's coming from the opposite direction. If you work for a game company, you can ask your engineers to add some additional code to your model exporter, so that when your models are exported from Max or Maya, etc, the exporter will recognize cases were the normal of the polygon and the normal of the UV coords don't match. In those cases, the exporter can flip the UV normal back the right way for you without effecting the unwrap at all. If they need

4 help figuring out how to do that, this is a good place to start. If you don't work at a game company or have access to programmers that can just whip up stuff like that, your best bet is just to avoid using mirrored texture coordinates all together. That's probably not what you wanted to hear since you'll have to use a lot more texture space to get the results you want, but that's the best you can do. Overlapping UVs Often when applying UVs to a model there are several parts of the model that share the same part of the texture, so the UV coordinates of those pieces are all on top of each other. This will work, but requires some special handling. Generally, programs that create normal maps, like NormalMapper, get all confused if you have overlapping UVs - so the trick is to make a special copy of your low res model that's used only for generating the normal map. On that copy, delete all of the polygons that have overlapping UVs except for one set. That way, when you generate the normal map using the copy, there are no overlapping UVs, but you can then apply the normal map to the original model that has overlapping and evething will work fine. Splitting Up Your Model Many models require more than one normal map. In these cases make a copy of the original low res model, break the copy into multiple pieces, one for each normal map. Put all of the polygons that will be using the first normal map in the first piece, all of the polygons that will be using the second normal map in the second piece, and so on. Then generate the normal maps using the seperate pieces as if each piece was its own model. Once the normal maps are created, you can apply them to your original model. Sometimes it is also necessary to split up a complex model into several different peices even when it's just using one normal map. If you try to generate the normal map for your whole model and it comes out very messy looking with high res details in the wrong places and lots of errors, you can often fix the problem by making a copy of your low res model and breaking it up into pieces along the UV seams. Generate a normal map for each piece seperately and then put all of the parts of the normal map together in a paint program to create a single normal map for your original model. Tips For Creating the High Poly Model The high poly model will only be used to create your normal map. Since it won't be rendered in real-time, you can use as many polyons as you want - even millions! You can model every rivet and every nail head, every skin wrinkle and every pore. You can sub-divide the model until the wireframe is do dense it looks like one solid color. (This kind of modeling is very gratifying for those of us who've been stuck in low poly land for many years.) The only practicle limitation is the amount of time it takes to generate the normal map. Here are some tips to keep in mind when creating your high poly model: You Don't Need UV Coordinates That's right! The high res model does not need UV coordinates. It's just a high detail mesh. Only the low res model needs UV coordinates. Optionally, you can apply UV coordinates to the high res mesh and then apply a bump map to it. Then when the normal map gets created, all of the detail from the high res mesh AND the bump map will go into the normal map (I'll get into more detail about how this is done on page 3 of the tutorial), but this is not required. Be Careful With Straight Extrusions Details that extend straight out from the surface of the mesh don't translate to the normal map very well. If you select some faces on the high res mesh and extrude them straight out from the surface, the detail won't show up in the normal map or it will not look very good because the normal map contains surface direction, not surface height. Consider extruding the faces and then scaling them down a little at the top so that the sides are slightly sloped. Rounded details always translate into the normal map better than sharp grooves and ridges. Remember Your Normal Map Resolution Keep in mind that all of the detail in the high res model is being created for the purpose of creating a normal map. The normal map will be

5 created at a limited resolution (256x256, or 512x512, etc). If you put details on the surface of your high res mesh that are smaller than the pixel size of your normal map, you're wasting your time because they won't show up, they won't be clear. Remember that as you add small details to your high res mesh. I hope that these modeling tips help you get better results when creating your normal maps. This is certainly not a complete list of tips for creating the high and low res models. If you know of additional information that I need to add, please me!

6 NORMAL MAPS: PART II - page 3: Methods for Creating Normal Maps Methods for Creating Normal Maps In the first tutorial, I outlined two methods for creating normal maps. On page 4 of the first tutorial I discussed converting a bump map to a normal map in Photoshop. On page 5 of the tutorial I explained how to generate a normal map from a high and low detail model using ATi's NormalMapper program. In this section I'll explain some additional (and better!) methods for creating normal maps. Normal Mapping Tools in 3DS Max 7 3ds Max 7 ships with some pretty impressive tools for creating normal maps of all types. Since I got the beta version of Max 7, I haven't used NormalMapper anymore. Max's tools are just very good and very easy to use. (There are some bugs in Max 7's shaders for displaying normal maps though. I'll discuss those on page five of the tutorial.) Ben Mathis has written a great tutorial for creating normal maps using the tools in Max 7. You can find it here. Thanks Ben! Normal Mapping Tools in Maya 6 Maya 6 has some great tools for creating normal maps. Jeff Parrott has a simple tutorial on his web site that shows how easy it is to use the normal mapping tools in Maya. You can find his tutorial here. Normal Mapping Tools in Softimage XSI I think that XSI was the first major 3D authoring app to feature tools for creating normal maps. Bartek Dabkowski has created a tutorial that shows how to use these tools. You can find it here. Normal Mapping Tools in Lightwave While Lightwave doesn't have any "built-in" tools for generating normal maps, it has a very flexible plug-in system. Marvin Landis has taken ATi's NormalMapper and turned it into a plug-in for Lightwave's Modeler. He even wrote a nice interface for it! You can get his plug-ins here. Nvidia's MeLODy Nvidia has created a tool called MeLODy that can create normal maps. It also automates the process of creating LODs. You can get it here. To create a normal map for your model using MeLODy, install it and follow the steps below: 1. Create a high and a low res version of your model. The low res version needs UV coords. 2. MeLODy supports OBJ or 3DS format so export both of your models in one of those two formats. 3. Open MeLODy and click the "Normal Map Settings" button. 4. By defualt, MeLODy is set to create its own set of texture coordinates for your low res model. You can leave it that way if you want, but most artists prefer to use their own texture coordinates. You can use use your own coordinates by choosing "Use Existing Normal Map Texture Coordinates." Click the "Close" button at the bottom of the panel. 5. Now you're going to load in your models. In MeLODy, the low res model is called the "Working Model" and the high res model is called the "Reference Model." Click the "Load Working Model" button and browse to the location of your low res OBJ or 3DS file. Now that the low res model is loaded it will appear on the right side of the viewport. 6. Click the "Load Reference Model" button to load the high res version. Browse to the location of your high res OBJ or 3DS file. The high res model will appear on the left side of the viewport. 7. Now you're ready to generate your normal map. Just click the "Generate Normal Map" button and MeLODy will create a normal map for your low res model using the normals of your high res model. 8. Once the normal map is finished, you can see where it has been saved

7 by clicking on the "Console..." button. If you don't get the results you were hoping for, MeLODy has a host of settings for tweeking the way the normal map is created. You can find a detailed description of the settings and how to use them in the User Guide that comes with the MeLODy installation. Creating A Normal Map Right In Your 3D App Did you know that you can create a normal map in ANY 3D program? You don't need any special plug-ins or exporters or extra tools at all when you create a normal map with this technique! I'll explain how to do it, but first there are a few limitations: Your low res model must be a flat plain. The low res model must have a planar UV projection (flat texture coordinates). You can't use this for characters that have specific unwrapped texture coordinates. This technique is really good for environment normal maps like bumpy ground, rock walls, bricks, metal panels, etc. I'll explain the steps to set it up for 3DS Max, but you can do the same thing in ANY other 3D program. Here's how to do it: Open 3DS Max and create a directional light. Rotate it in world space to 0,-90,0. Set the light's color to 255,0,0 (red). Set the multiplier to Create another directional light. Rotate it in world space to -180,-90,0. Set the light's color to 255,0,0 (red). Set the multiplier to 0.5. Create a third directional light. Rotate it in world space to 90,-90,0. Set the light's color to 0,255,0 (green). Set the multiplier to Create a forth directional light. Rotate it in world space to -90,-90,0. Set the light's color to 0,255,0 (green). Set the multiplier to 0.5. Create one more directional light. Rotate it in world space to 0,0,0. Set the light's color to 0,0,255 (blue). Set the multiplier to 0.5. Select each of your lights and check the "Overshoot" box under Directional Parameters so they'll light things that are outside of their cone. Choose "Rendering->Environment..." In the Environment panel set the Ambient color to 127,127,127. Create a free camera. Set the camera rotation to 0,0,0 in world space. Click the "Orthographic Projection" check box so that the camera becomes orthographic (so it has no perspective). Now you create a high resolution model. Apply a material to the model that has a white diffuse color. When you render your model from the point of view of the camera, you'll get a normal map! Here's what the scene looks like when it's all set up:

8 I like creating normal maps this way because they render much faster and I don't have to use any external software. I got the idea for this technique from this web page: If you're having a hard time setting it up, you can download a sample file for Maya, Max, or Lightwave at the bottom of that page. Using My Normal Map Shader In 3DS Max 6 and 7 When you boil it down, a normal map is just an image of your high res model where every pixel is colored to represent surface direction instead of surface color and lighting. With this in mind, all you really need to create a normal map is a material or shader on your high res model that gives you normal colors instead of surface colors. I've written a shader in HLSL FX format that does exactly that. You can grab it here. When you apply that shader to your model in 3ds Max 6 or 7 (follow these instructions to apply it) you get an instant normal map. Just take a screen shot of your model, open it in an image editing program, crop it, and save it out. You're all done! The main draw back to this method (and the previous one also) is that you can't make a normal map that wraps around a 3d character. This technique is best for creating tilable normal maps that you're planning to apply to the environment. Normal Map Formats Since a normal map is a way to use color data to represent surface normals, there are several ways that the color data can be used - or several normal map "formats." In order for your normal map to give you the correct results, the program that generates the normal map and the program (or shader) that uses the normal map must use the same format. Tangent Space vs Object Space vs World Space The main way in which normal map formats differ is in what "space" they use. "Space" refers to the point of reference for the X,Y, and Z values (the R,G, and B of the normal map). All of the info that I've been discussing in my tutorials so far has been covering normal maps created in "Tangent Space." Tangent Space normal maps use texture coordinate space, so X and Y are the U and V of the texture coordinates and Z is the surface normal. Tangent space normal maps appear mostly light blue (127,127,255) because the Blue channel represents the direction that the underlaying model surface is facing. The red (X) and green (Y) channels are for offseting that direction. Tangent Space normal maps are best used on characters that deform and when tilable normal maps need to be applied to curved surfaces in the environment. Object Space normal maps use the orientation of the model as their X, Y, and Z. Y is most commonly in the direction of the top of the model while X is to the left of the model and Z in the direction the model is facing. Object Space normal maps usually appear rainbow colored because they represent normals that face in every direction instead of just a 180 degree hemisphere like Tangent Space normal maps. Object Space normal maps can be used on rigid objects that need to rotate and have a unique set of texture coordinates (not a tiled texture). World Space normal maps are very similar to Object Space normal maps - except they use the X, Y, and Z of the world as their coordinates. They also appear rainbow colored. Because they depend on the world coordinates, you can't rotate a model with a World Space normal map and have the lighting still appear correctly. For that reason, World Space normal maps can only be used on static objects that have a unique set of texture coordinates. In my opinion, Tangent Space normal maps are the best. They can be used for everything. You can apply them to deformable characters, rigid objects, and world geometry. Unlike Object Space or World Space normal maps, Tangent Space normal maps can be created to be tilable and then applied anywhere - on the walls, ceilings, floors, etc. They are a bit more expensive computationally, but this extra expense is insignificant on today's graphics hardware.

9 Positive or Negative Y When using Tangent Space normal maps, the most common difference in formats is the direction that the green channel is lit. Some programs light the green channel from the left (postive Y) and others light the green channel from the right (negative Y). Some programs give you the option to choose positive or negative Y. If your normal map isn't being lit correctly, the first thing that you should try is to flip the green channel. Just open the normal map in Photoshop, select the green channel, and choose "Invert." That will give you the same result as if you had rendered the normal map in the other format. So there you have it: A bunch of extra stuff about generating normal maps! Now I bet you're asking yourself, "If my normal map has problems, can't I just open it in Photoshop and paint out the errors?" The answer is a most definite and totally confident "sort of." :0) There are a few things that you should know about editing your normal map in a paint program. I'll discuss those on the next page.

10 Mip-Maps NORMAL MAPS: PART II - page 4: Tips for Editing Normal Maps Tips for Editing Normal Maps So you've created your normal map, you apply it to your model and it looks great! -- Except for those annoying seams and those few spots that didn't turn out quite right. Well that's easy, you can just open the normal map in Photoshop and fix those with the clone tool, right? WRONG! A normal map is very different from a regular texture, because the colors represent the X, Y, and Z values of a directional vector instead of just a color. Not only that, but the three values together must yield a directional vector whose unit lenth is one (a normalized vector). This means that only a very specific set of colors can be used. So you can't just go painting colors and expect them to give you good lighting when used as a normal map. "Can't I just paint with the colors that are already there?" - Yes, but if your brush has a soft edge, the blending will give you colors that no longer result in a vector length of one. Just about any editing that you do in your paint program that doesn't preserve the exact colors that were there when you started will give you incorrect results. "So I can't edit my normal map at all in a paint program?" - You can. But there are a few things that you need to watch out for and a few tips that will help you get better results. Read on! Re-normalization The main thing that you need to do to avoid the problems that I mentioned above is to "re-normalize" your normal map. You can paint on it, and use the clone tool and edit all you like as long as you make sure all of the colors result in a vector with unit length one (normalized) when you're done. Luckyly, Nvidia has created a very cool Photoshop plug-in that will do this for you. When you're done with your editing, you just run the plug-in and it looks at every pixel in the normal map and adjusts the colors so they give you normalized vectors! You can grab the plug-in here. Download the "Adobe Photoshop Normal Map Plugin" and install it. Once you're done with the installation, follow the step below to "re-normalize" your normal map If you added layers while you were editing, flatten your image so it's all on the base layer. Get rid of any alpha channels if you have them. Choose "Filter -> nvtools -> NormalMapFilter..." This will bring up the Normal Map filter options window. There are options here for converting a bump map into a normal map, but since we already have a normal map, we're just going to use the normalization feature. Under "Alternate Conversions" choose "Normalize only." Click "OK." That's it! Your normal map is now normalized again, just like it was before you started editing. Now you can save it and apply it to your model. Seams One of the main problems that occurs when creating normal maps is that there are seams at the edges of UV regions. This problem can be solved in several ways. The best way is to have the program that creates the normal map expand the colors of the map beyond the edges of the UV regions. In some normal map creation software this is called "edge padding" and in others it's called "expand border texels." There may be other names for this feature, but that's the first thing you should try if you're having trouble with seams. If that doesn't work, another method is to paint a small buffer strip of light blue (127, 127, 255) along both of the edges of the seam. This light blue color represents the vector that points straight out of the surface. If both edges of the seam are using this color, they'll match each other better. You might lose a little of your high res detail, but at least you won't have an ugly seam. I recommend only using this method if you really need it.

11 Real-time textures use mip-maps to reduce texture flickering and sizzling when the texture is smaller on the screen than it is in resolution. Mip-maps are smaller copies of the texture. The smaller the texture appears on screen, the smaller the copy of the texture that gets used. Usually the mip-maps are automatically generated when the texture is used and the artist doesn't have to worry about them at all. With normal maps, it's a different story. Mip-maps are generated by copying the texture and scaling it down. For regular textures, this works fine, but for normal maps, the scaling also de-normalizes all of the normals. That means that as your model moves away from the camera, all of the normals will get de-normalized and the lighting on your model won't look that good. The solution to this problem is to make sure that when mip-maps are created for normal maps, the mip-maps get renormalized. This is probably a step that a graphics engine programmer could do pretty easily. If you don't have a graphics engine programmer handy, you can do it yourself by using DDS as your image file format. 3DS Max will read DDS image format. DDS stands for Direct Draw Surface. It's an image file format that is used natively by DirectX. It contains extra information that DirectX can use - like mip-maps. Nvidia makes a plug-in for Photoshop that will read and write DDS format. The plug-in allows you to do a ton of stuff with the image when you save it in DDS format. Most importantly it allows you to normalize all of the mip-maps. If you installed the plug-in that I talked about above in the "Re-normalization" section you already have it. If not, you can get it here. Once you're done with the installation, follow the step below to "re-normalize" your mip-maps. 1. In Photoshop open your normal map and choose "Save As..." Pick DDS format and click "Save." 2. When you click the Save button, this options dialog will appear that allows you to specify all of the parameters for saving your image. I was really impressed with how much control all of these options gave me over exactly what I wanted to do with my image. You can do a lot more with DDS format than we're going to cover in this tutorial. 3. Under MIP Map Generation, choose "Generate MIP maps." The plug-in will automatically create mip-maps for your normal map when you're ready to save. The mip-maps will be stored as a part of the DDS format image. 4. Click on the "Normal Map Settings..." button to access the normal map conversion options. The following window will open:

12 5. Make sure that the "Convert to Tangent Space Normal Map" box is checked. Under "Alternate Conversions" choose "Normalize only." Click "OK." These settings will ensure that when your mip-maps are generated, they will be re-normalized. Now click the "Save" button. Now you've got a DDS image saved that has correctly normalized mip-maps. The lighting detail will remain correct regardless of the model's distance from the camera. Texture Compression To allow for as many textures as possible, most video games use some type of texture compression. Most use S3TC, DXTC, or some type of palletization. These types of texture compression work well for diffuse textures, but they don't work so well for normal maps. All of these compression techniques change that colors of the image so that it can be smaller. This causes the normals to become denormalized. The compression also introduces other artifacts. These artifacts aren't as obvious on a diffuse texture, but on a normal map they really stick out. The following table illustrates the effects of texture compression on a normal map. The left column shows the normal map itself with several different types of texture compression. The right column shows the lit model with the normal map applied.

13 While the file size savings is significant, the quality loss is also significant with all types of compression. It's pretty obvious from the chart that 8 bit compression is not usable at all. You might be able to use 16 bit, but it's only 2:1 compression. There is very little difference between DXT5 and DXT1 except that DXT5 also has an alpha channel (not shown here) which can contain extra information - like a height map. Obviously, the best thing to do is to not use any texture compression at all on normal maps. If you absolutely have to use compression, DXT1 seems to be the best option. It has the smallest file size and is better looking than 8 bit. There is another option, but it requires that your normal map be changed around a bit and also that your shader be edited slightly. DXT5 gives the most quality to the green channel and to the alpha channel. We can take advantage of this to "hijack" the DXT5 format and turn it into a normal map compression format. First we need to re-arrange the data in the normal map. Take the red channel data (X) and put it in the alpha channel. Now make the red and blue channels black. Now we need to adjust the shader to switch the data back around for us. The shader needs to be told that the red channel data is in the alpha channel of the texture and that it needs to calculate the blue channel values itself. This is possible with a little algebra because we can assume that the vector that results from R,G, and B will be unit length one. If you are able to make these changes to both the normal map and the shader, you'll get 4 to 1 normal map compression with very little quality loss!

14 All of the normal mapping shaders on my web site now offer this compression solution as a second technique in the shader - so you can get four to one texture compression and good normal map quality as well. I hope that the tips on this page have been helpful for you. I've learned that the data in normal maps is very sensitive and can't just be treated like any other color map. I hope that as a result of the things I've written, you'll be able to more successfully handle and edit normal map data. In the first Normal Map Tutorial, I explained how to use the Nvidia Cg Plugin for 3DS Max 5 to apply your normal map to a model. On the next page I'll explain lots of other good methods to apply your normal map to your model. Read on!