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What is the difference between Normal vs. Bump Map

Posted on 2011-02-18
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Can anyone explain what the difference is between a Normal Map and a  Bump Map?  I am working on developing 3D models for Unity and not quite sure the difference now.  I have always used Bump Map for depth-ness.
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Question by:ModifyMe
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by:Jose Parrot
ID: 34928383
The difference is in the way of using the image.
The normal bitmap is the image itself, used as a picture, texture or bumpmap.

As a picture, the bitmap appears as a single image, for example, as a background for a scene.

As a texture, the bitmap is applied on a surface to make it appear like the material or color existing in the image. We can repeat the image such that a small image covers a large area. In this case, the image needs a special attribute, say, its left side should be continuous to the right one, as the bottom side must link to the up side as well.

As a bump image, the attibute of a texture should exist too, if we repeat the image. The difference in this case is that the colors or gray levels are interpreted as heights in the objects' surfaces, emphisizing the texture effect with shadows.

Jose
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Sean Scissors earned 2000 total points
ID: 34929374
In dealing with games Normal Maps are more commonly used which is actually a type of bump map. Games like Gears of War used Normal Maps to create very highly detailed looking characters in real time. Normals is a term used to depict the inside/outside of a surface. 3D programs allow us to "bake" these normal maps into textures. What is then done is you can take a large character at 1million polygons (there is no limit) and then bake the normal map texture onto a much smaller, say 5000 triangle character model.

Example:
Model 1(high poly) - http://www.unrealtechnology.com/media/upload/Image/ue3_char1.jpg
Model 2(low poly) - http://www.unrealtechnology.com/media/upload/Image/ue3_char2.jpg

Ending result baking normal map from high poly to low poly charcter - http://www.unrealtechnology.com/media/upload/Image/ue3_char3.jpg

In games nowadays with better technology Normal maps are still being used but new types of bump maps like Parallax Occlusion maps are more popular. Parallax Occlusion is like a normal map but it differs in that it is calculated based off of the camera angle and not just the light.

In other words while the GeOW character looks good, if you look at a 90 degree angle the bump isn't seen. Whereas with Parrallax Occlusion, the bump is seen from any angle just as much as the next due to it being based off of the actual camera angle within the scene.

FYI: Gimp has a Normal Map plugin that easily allows you to create and even preview normal maps on a texture. If you have any other questions let me know.
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Author Closing Comment

by:ModifyMe
ID: 34929520
Wow, what a great explanation!

Thank you!

Just curious, how does a 3d artist create a 2mil poly character you depicted?  Is that a scan?
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Expert Comment

by:Sean Scissors
ID: 34929551
Well in that case they used a 3D modeling program albeit something like Autodesk Maya (which I have used for a about 4 years) 3Ds Max, Cinema4D, Zbrush..etc. I mentioned 5000 triangles because in games, having to be rendered in real-time, characters and objects are more often then not rendered in triangles (3 sides) instead of Polygons (4 sides) in order to save space. Like I said with Normal maps; If you create a high poly character and then map the baked normals to a low poly you can create a good looking character. In movies this isn't an issue because 3D characters are pre-rendered rather then being rendered in real-time like a gaming engine does.
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Author Comment

by:ModifyMe
ID: 34929646
Thank you!
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Expert Comment

by:Sean Scissors
ID: 34930012
Your welcome. Let me know if you have any other questions. There's a lot to learn about the difference between modeling for games and modeling for movies.
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Expert Comment

by:Jose Parrot
ID: 34934959
Ooops, I have misunderstood the question, but Scissors85 answer was really good.
Why grade 9.1? It was a brilliant answer.

Jose
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