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《现实主义与造型》史蒂芬.斯塔尔伯格  

2006-06-15 14:56:08|  分类: 其他东西 |  标签: |举报 |字号 订阅

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Realism and Shading
Steven Stahlberg

现实主义与造型
史蒂芬.斯塔尔伯格

译:大饼 2002.5

The devil's in the details
I'll make a sweeping statement here - good cg pays attention to the details, bad cg doesn't.
This doesn't mean such an image necessarily and always has to be realistic, like a photograph is realistic - but in practise, it turns out that's usually the direction it should be taken.
First let me define what I mean by 'realistic detail' here.
The universe around us, the one outside our computers, has everywhere we look a certain hard-to-describe chaotic, natural ‘richness’, the opposite to ‘mathematical perfection’; the dirt and dust on our man-made things, the accidental factors that flaw them, the dents, cracks, spots, mold and rot, the branching of trees, the varying shapes of mountains... The poor 3d artist has to jump through all sorts of hoops to achieve this kind of richness. This is because what we're dealing with in cg is just numbers - mathematical perfection. What we enjoy resting our eyes on most in the world around us - the precarious balance between chaos and patterns, randomness and sudden discontinuity, contrasts, is all alien to the computer, in fact the direct opposite to what it does best.
True, the computer is good at fractal detail, and patterns, but there is a uniformity and 'coldness', a sharpness and smoothness, that becomes boring and ugly without the other factors mentioned. (I'll get back to that later.) So a single layer of strong Fractal Noise just isn’t enough - we want more, qualitatively speaking. More of what, exactly?
Every successful work of art has (among other things) some or all of these aspects I mentioned before:
1. Detail (complexity)
2. Variation of detail
3. Discontinuities (and edges)
4. Patterns
5. Contrasts
6. Randomness, Chaos (applied to all the above)
How to apply these points to your images? Here are 6 things to remember, to have strong kung fu in cg.
细节带来的麻烦
我要在这里做一个彻底的陈述:好的CG要在细节上下功夫,差的则不然。
这并不意味着一个图像中要有丰富的细节或者总是要做成现实主义的作品,就像相片一样真实,但在练习中,这应该是个努力的方向。
首先,让我来说说我的“现实主义细节”的意思。
我们周围的世界,计算机之外的那个世界到处都充满难以描述的混乱,与大自然的“富饶”相对的是“数字的完美”;这是数字化的一个缺点,人造的东西很脏很乱,导角,裂缝,污点和腐烂,树的分支,山脉的形状变化等等,可怜的3D艺术家不得不克服所有的束缚来实现这种“富饶”,这是由于我们在CG中要面对的东西是仅仅是数字化的完美的一部分。形成对照的是,我们喜欢把目光停留在我们周围的世界中-混沌与有序之间的,随机与突然中断之间的不稳定的平衡等等所有的与计算机不同的,或者说与之相反的世界中。
实际上,计算机很擅长分形的细节和图案,但是有一样必须提及,那就是表现尖锐的和光滑的这两样不同的事物,只用分形噪波中的一个单一的层是不够的,我们需要更多,更多什么呢?
每个成功的艺术品都具备以下的几点:
1. 细节(复杂性)
2. 细节的变化
3. 不连续(和边缘)
4. 图案
5. 对照
6. 随机的混乱(应用于以上几点)
如何在你的图像中应用这几点呢?要想成为CG高手,有6件事你要记住。
1. Shading
Add shading to the objects in the scene, this raises the complexity/variation level. This may seem obvious, but I start at the beginning to better make my point. In Maya it's just a matter of placing at least one light, Don't use high incandescence or ambience too much, since these will tend to blow out the shadows.
Note that the ambient light is too strong in the left one below (a common mistake), and corrected at right. We want the darkest shadows to be dark, almost black but not quite, except maybe for small parts of the image. (Unless we're going for a high-key scheme, I'll discuss that in the lighting segment.)
1.明暗关系
为场景中的物体添加明暗关系,这样做会提高复杂度和变化的级别,这是显而易见的,但我在一开始就指出这一点。在Maya中,这只是放置至少一盏灯光的事情,不要过多地使用白炽灯或者环境灯,因为这会使阴影的效果减弱。注意,环境光在左方或者下方时不要太亮(这是个很普遍的错误),正确的应该在右方,我们想得到是一个图像中很小部分的一个最黑的黑影,差不多是黑的但黑得不是很彻底(除非我们打算制造一个高调的气氛,到时候我们再讨论这个问题)。


  
2. Shadows
Now let's add shadows - this also seems simple enough, but this step is very often skipped, and it's amazing how much some simple shadows can add to an image. We add them to all objects that are not transparent, except if the shadow directly interferes with what we are trying to achieve of course.
2.阴影
现在我们添加阴影,这看上去很简单,但这一步经常被忽略,在图像中加入阴影是很容易的。除非阴影直接妨碍了我们要表现的东西,不然我们就应该把所有不透明的物体加上阴影。


  
3. Textures complexity
All textures must be above a certain level of complexity, or they must be very muted and subtle. NEVER use a simplistic texture, like a procedural (fractal noise, ramps etc), on it's own with very high contrasts, or strong colors. Watch out for strong colors - a surface that only reflects light and emits none of its own, should never have a 100% saturated color on it. Also, on composition - don't cover too much of your image area with a very strong color.
3.纹理的复杂性
所有的纹理的复杂程度必须超出某个等级,或者非常精细。决不要使用过分简单的纹理(分形噪波,撞音等),在纹理上要有高度的对比和强烈的颜色。注意强烈的颜色,一个表面只能反射光线而它本身不能发光,不要在它的身上使用100%的饱和度。所以,在合成时,不要用强烈的颜色覆盖你的图像的太多区域。


  
4. Modeling or texturing detail
Thin planes not very far away must have some thickness, bevels should always be added if visible, subtle details - there are never enough, so add more (fillets, flanges, ridges, dents, seams, bolts, panels, defects, dirt, etc), and the polygon resolution must not be too low in rounded objects (if you can see the facets, it's too low). Points 3 and 4 is where 50 to 90% of all the effort and time should be placed (depending on the image) - a good general rule is: The More Detail And Variation The Better. Now I don't mean you should go putting 10,000 exact copies of rivets on a wall - there's no variation in that. To stick with the riveted wall as an example - you should add as many rivets as will look cool (never add detail that will not be seen!), but make sure some of them are different from the others. Also make sure they are not evenly spaced and in perfectly straight lines (and maybe some are missing), that the wall is slightly bumpy and buckled, maybe scratched and dented, that some dirt has collected around the rivets and maybe some rust has run down the wall from some of them, the wall should have a different texture at the top than at the bottom, etc etc...
4.模型和纹理的细节
距离我们的视线不是很远的薄板是有厚度的,如果看得见,它是有导角的,微妙的细节永远都不是多余的,添加多一些(边缘,接缝,毛边,污垢,残缺等),圆形物体的模型分辨率不能太低(如果你可以看得见facet,那么它的分辨率就太低了)。在第3点和第4点上,要花费50-90%的精力(就图像而言),一个普遍的规则是:越多的细节就有越好的效果。现在我不是说要你在墙上复制10000个钉子,那没有必要,这是一个例子,如果看上去效果很好的话,你可以在墙上加一些钉子(不要再看不见的地方添加细节),但你要确定有一些跟其他的是不一样的。还要确定这些钉子不是在一条完美的直线上分布的,墙不是平的,可能有凹坑和划痕,在钉子的周围可能很脏,还有很多铁锈,墙的顶部和底部是不同的,等等等等。

5. Realistic lighting FX
6. Post effects
Motion blur, if you have fast movement (fast as measured in screen pixels per frame, not absolute speeds). Depth of Field if necessary/applicable. And lastly: Gaussian blur and film grain, in that order (do that always, a computer will render things too sharp and smooth every time).
5.现实主义的灯光特效
6.加速特效
运动模糊,如果有很快的运动(不是绝对速度,而是屏幕上每帧的像素)。场景深度,如果有必要的话。最后:高斯模糊和电影颗粒。(保持这些特效,计算机每次都会渲染得十分光滑)。


Additional notes:
Be careful with Glows and Lensflares - beginners very often use too much of these.
The concept of multiple pass rendering for later compositing is a very useful one, and can be used in many different ways to speed up production, and add flexibility and choices towards the end of a project. It can be used to separate light sources and their effects on the scene, it can be used to create your own motion blur, it can be used to separate glow effects, particles, foreground/background, super-high-resolution parts from normal or low res, raytraced effects from raycast, faked fog and faked Depth-of-Field effects, etc.
For printing, you can the final image in Photoshop 200 - 400% without obvious loss of quality, especially if you add grain. A big problem with cg in most cases is that it's too sharp anyway, especially at high resolutions, so lower the rendering resolution and save time as well.
附:
使用晕光和发光效果时要小心,初学者经常使用过多的晕光和发光效果。多通道渲染的观念在最后的合成中是很有用的,可以用很多种不同的方法来加快完成的速度,增加了灵活的和可选择的方案。这样也可以在场景中将灯光与它们的效果分离开,可以建立你自己的动作模糊,可以使用单独的晕光效果,粒子系统,前景和背景,在中低级的物体上建立超高分辨率的部分,还有光线跟踪效果,伪造的雾气和伪造的景深效果等等。
如果用于印刷,你还可以在Photoshop中将图像放大200-400%而没有明显的质量损失,尤其是当你添加了颗粒效果的时候。CG的一个大问题是它总是十分精细,尤其是高分辨率的时候,于是,较低的渲染分辨率会节省很多时间。


About textures
The best texture is almost always a retouched photo. Why? Because we're directly using a piece of 'Reality', with all that entails in regards to chaotic patterns, detail and variation.
The best tools to use for photo retouching are the clone/stamp tool, and filters applied in masks with varying degrees of feathering on the mask borders.
The worst texture is usually a simple straight forward procedural with no layers.
Sometimes worse are the ones hand painted from scratch in a computer. The reason for this is partly that painting anything is very difficult, and especially using a computer. Mainly there's the problem with the pen tool. A real airbrush, for instance, should never be used freehand, the results are almost always terrible, it should always be masked one way or another. Same thing applies to the computer.The reason the result looks so bad (if we don’t watch out) is the uniformity and smoothness of the lines, sometimes with the little globules at the start and end of every stroke.
Avoid repeating textures at all costs - an example: you have to shade the floor of a large hall with a granite texture. It's a nice texture, but the problem is it's not big enough, it has to be repeated 100 X 150 times at least. But when you render a view from average human eye-level looking across the hall, you see this horrible weird zig-zag pattern extending across the floor. Mirroring and Staggering doesn't seem to help, in fact Mirroring made it worse by making the zig-zags bigger. How to fix it?
One way is to use a 'smear-map' with much less repeats than 100 layered on the main texture - a subtle one will be enough. Another way is to layer textures on each other, with different repeats. Say you have a checkered pattern that repeats 12 times across a floor.
Another way is to open the image in Photoshop, paste it as many times as you like in a larger window, and then make sure it's non-repeating by painting and retouching, then reapplying it in your shader with less repeats. But be aware that this creates larger image files, eating disk space, RAM, and slowing shader-updating.
关于纹理
最好的纹理通常都是经过润饰的相片,为什么呢?因为这样我们可以直接使用“真实”的东西,包括混乱的图案,细节和变化。
润饰相片最好的工具是复制和印章工具,还有在边缘经过羽化处理的遮罩中应用不同等级的滤镜。
最差的纹理是经常没有分层的使用简单的整齐的平铺纹理。
有时更差的是用计算机手绘的草稿作为纹理。原因就是手工绘制纹理是很困难的,尤其是使用计算机。主要的问题是使用钢笔工具,举个例子,一个真正的喷笔决不会只是徒手使用,这样做的结果是很糟糕的,应该在某处进行一些遮挡,在计算机中也是同样的道理,否则结果会很差(如果我们不小心的话),看上去会很光滑,很整齐,每一笔在开始和结束时都有一些小水滴。
在所有的图像中消除重复部分,一个例子:你应该在一个花岗岩纹理的墙下的地板上进行遮光处理。那是一个很好的纹理,但是问题是贴图不够大,你不得不重复至少100×150次。但是当你渲染视图时,你会发现在地板上有一个很怪异的折形图案。镜像和抖动处理并没有效,实际上,就是镜像处理使得地板出现了折形的图案,如何修补呢?
一个方法是使用“污点贴图”并且至少在主纹理重复100层,如果足够精细的话,一个就可以了。另一个办法是将层的纹理互相重叠,使用不同的重复。在一个地板上将一个图案重复12次。
另一个方法是在Photoshop中打开图像,在一个大窗口中粘贴数次,然后通过绘制和润饰确信没有重复后,将它以最少的重复数应用到你的场景中,但是注意,这样创建了一个很大的图像文件,消耗的磁盘空间,内存,还减慢了图形的刷新速度。
 

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