On HDR lighting/关于HDR照明

狂风大尉

On HDR lighting/关于HDR照明
感谢Ghostxx的来源提供


There have been many lively discussions recently about how best to use HDR images for lighting in 3dsmax and vray.
最近有很多活跃的讨论关于如何最好地使用HDR图像在3dsmax软件和Vray里得到更好的照明。

The latest round came after the release of Peter Guthrie’s excellent HDR sky images. Time for me to add my two cents on the subject.
最新一轮缘起发布的Peter Guthrie’s excellent HDR sky images。我来提出我的两个观点。
  
One recurring question is how to obtain sharp shadows that match the photos used to create the HDR map.
一个反复出现的问题是如何获得锐利的阴影用HDR贴图。

Often times, sunny-sky HDR images, for instance, only seem to yield renders with big, blurry soft shadows instead of the sharp shadows you’d expect from looking at the map.
通常,晴朗的天空的HDR图像,例如,只有似乎产量呈现大、模糊软阴影而不是锐利的阴影,你应该期望在地图上寻找。

This is especially obvious when working in LWF or with particularly washed out HDR maps.
这是特别明显的当工作在LWF流程或使用特别黯淡的HDR贴图。

There are traditional workarounds for this.
有传统的解决方案这个。

One consists in adding a VraySun or a direct light to the scene and align them with the sun in the HDR image.
一个是用VraySun或直射光添加到场景里,使之与太阳在HDR图像里的位置匹配。

Another is to use the “Smart IBL” system, which does exactly the same thing but automates the process.
另一个是使用“Smart IBL” system,它做完全相同的事情,但是这个过程完全自动化。


But there’s another, simpler way to obtain sharp shadows from nearly all HDR maps – shadows that are 100 per cent consistent with the map, authentic-looking, and do not involve adding any other light sources.
但还有一个更简单的方法来获取尖锐的阴影几乎完全从HDR贴图上,100%符合贴图,看起来像真的,不涉及添加任何其他光源。

Most of the time, lowering a map’s gamma will do the trick.
大多数时间,降低一个贴图的gamma 是一个讨巧的技巧。

Yep, that’s it. What this hack does is to increase the contrast of the HDR image, thereby artificially boosting its dynamic range. It is most effective when using maps that have a reasonably high dynamic range, strong and well-defined light sources (spotlights, a sun, etc.), and sufficient resolution.
是的,就是它。这个BUG确实可以提高HDR图像的对比度,从而人为地提高它的动态范围。它是很有效当你使用的图片有一个合理的高动态范围贴图、强烈和明确的光源(聚光灯,一个太阳,等等),和足够的分辨率。

It also helps if you’re using an accurate rendering methode for GI – using a very low-res irradiance map will make it more difficult to generate sharp shadows than using brute force sampling.
它是很有帮助如果你使用一个准确的GI计算方式 -使用非常低分辨率的irradiance map将使它更难以生成比较好的阴影效果对比使用brute force。


The image below shows this trick in action using four home-made, very high-resolution HDR maps.
下图显示了这个技巧使用四个自制的、非常高分辨率HDR贴图。

The renders on the left use the maps with their default gamma of 1.0. On the right, the gamma was lowered to 0.5. Look at the difference in shadow definition and general “punchiness” (click for higher resolution).
左边的渲染使用默认伽马1.0的贴图。在右边,伽马降至0.5。看看不同的影子(点击查看高分辨率图片)。

The easiest way to do this is to use .hdr images in a VrayHDRI map, which features a live gamma control.
最简单的方法是使用.hdr图像在VrayHDRI贴图,其中包含了实时的伽马控制。

You can find the high-res maps used for this example in my Turbosquid account.
你可以找到高分辨率贴图用于这个例子在我的Turbosquid account帐户。




In all cases, render times were similar and none of the images were post-produced. Of course, the technique has drawbacks.
在所有情况下,渲染时间是相似的,并且所有的图像没有后期。当然,这种技术也有其缺点。

Changing a map’s gamma may change the light’s intensity, it may alter a map’s colours in a way that makes it difficult to use the map as a backplate, it may create unnatural reflections…
改变一个贴图的伽马可能会改变光的强度,它可能会改变贴图的颜色,使它很难使用当贴图作为背景时,它可能会产生不自然的反射…

If you use very high-dynamic range, high-resolution images, you may get sharp shadows out of the box with a gamma of 1.
如果你使用非常高动态范围、高分辨率的图像,你可能会得到尖锐阴影当使伽马是1的时候。

In other situations, the gamma treatment may happen to be  precisely what the doctor had ordered to compensate for an LWF image’swashed-out appearance. In other words, it all depends on the situation. But when all you’re getting are soft shadows and you want them sharp, this one is worth a try.
在其他情况下,这种伽马处理的方法可能弥补图像的漂白效果在线性流程下。换句话说,这完全取决于你的情况。但是当你想要软阴影变锋利,这值得一试。

hyui

Good to know!

ZackD

不错的分享，谢谢