什麼是displacement map??

[Cyclopsll]

有一天, 有一個朋友send了他的作品給我看
是一條掛著的毛巾, 但毛巾上面有他的logo
我問他是如何將個logo搞上去的
他說什麼displacement map就可以了

之後我就有找尋過有關displacement map的資料
而且在書中亦有介紹過相關的知識, 亦有在這裡爬文看過
但由於我只是一個Maya的初學者, 最多都只是明白初級的貼圖
bump map倒是明白, 但displacement map就是概念十分模糊

其實那是一種什麼的技巧來的?
可以用來做什麼?
我看書中有說過, 同一個model, 用不同的displacement map有可以有不同的外型, 是真的嗎, 我不是太明白啊

各位前輩可以提點一下小弟嗎?
thanks

[HammerChugoh]

For you to unerstand the concept of displacement map, you can think of bump map as a skill of modifying surface normal to give you an illusion that the surface is push up and down. And for displacement mapping, it actually move the surface(depends on different renderer, this process are handled in different process and approach), mostly a renderer(prman) will rasterize your geo into tiny micropolygon(as small as a pixel sometimes) and these polygon will be offset base on an images or a procedural function. so displacement can give you self shadow and offset in direction other than the dir of surface normal.