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<h1 class="post-title p-name">双向反射分布函数(BRDF)</h1>
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<h3 id="光的反射"><a href="#光的反射" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>光的反射</h3>
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<p>对于在某一点上发生的反射，我们通常认为：</p>
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<ul>
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<li>光进来打到了一个物体，被弹走后，改变了方向</li>
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<li>光线打到了某个物体表面后被吸收，再从物体表面将吸收的能量辐射出去</li>
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<h4 id="通过radiance-和-irradiance-来解释"><a href="#通过radiance-和-irradiance-来解释" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>通过Radiance 和 Irradiance 来解释</h4>
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<p>从某个立体角($\omega$)来的Radiance会打在dA上，在dA上转换成能量，并以光的形式辐射到另一个方向上去(dLr),即表现为出去的Radiance</p>
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<p><img src="../../images/reflaction_radiance_irradiance.png" alt=""></p>
|
||
<p>对于dA来说，其接收到的能量只考虑某一方向下立体角的Radiance,在投影后就可以计算dA接收到的Irradiance,Irradiance又会转换成Radiance反射出去</p>
|
||
<p>出于描述dA从某个方向接收到能量后向某一方向辐射的能量值的目的，我们定义了双向反射分布函数(BRDF)</p>
|
||
<h3 id="bidirectional-reflectance-distribution-function-brdf"><a href="#bidirectional-reflectance-distribution-function-brdf" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>Bidirectional Reflectance Distribution Function (BRDF)</h3>
|
||
<p>BRDF描述了dA表面是如何把一个方向收集到的能量反射到另一个方向去(定义收集到的能量如何如何往各个方向去分配(漫反射还是镜面反射))</p>
|
||
<p><img src="../../images/BRDF_define.png" alt=""></p>
|
||
<p>镜面反射下，反射出去的方向上分布了所有能量</p>
|
||
<p>漫反射下，吸收的能量会被均等的分配到各个不同的出射方向上去</p>
|
||
<p>BRDF本质上描述了光线和物体是如何作用的，因而BRDF项也定义了物体的不同材质</p>
|
||
<h3 id="反射方程the-reflection-equation"><a href="#反射方程the-reflection-equation" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>反射方程(The Reflection Equation)</h3>
|
||
<p>反射方程定义的是任意着色点，在不同的光照下，我们考虑任意一个输入的光照的入射方向对出射方向的贡献，并累加所有入射方向的贡献</p>
|
||
<p><img src="../../images/the_reflection_equation.png" alt=""></p>
|
||
<p>公式解释：</p>
|
||
<p>考虑任一不同方向的Radiance到图示的点，再通过BRDF的计算，可以得到出射的Radiance</p>
|
||
<p>存在问题：</p>
|
||
<p>从某个方向观察着色点意味着需要考虑所有到达这个着色点的光线，在光线弹射次数大于一次的情况下，能到达着色点的光线并非只有光源，还可能有其他面反射过来的光线(一个面接收光源照射后反射的Radiance还能够照亮其他面，产生递归问题)</p>
|
||
<h3 id="渲染方程the-rendering-equation"><a href="#渲染方程the-rendering-equation" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>渲染方程(The Rendering Equation)</h3>
|
||
<p>渲染方程在反射方程上考虑了物体自发光的情况，提高了通用性，几乎所有物体表面的光线传播都可以使用下列公式来总结</p>
|
||
<p>$$L_o(p,w_o) = L_e(p,w_o) + \int_{\Omega+} {L_i(p,w_i)f_r(p,w_i,w_o)(n\cdot w_i)dw_i}$$</p>
|
||
<ul>
|
||
<li>渲染方程与Blinn-Phong模型都假设所有方向向外(考虑所有入射来的方向为球心向整个半球的各个方向)</li>
|
||
<li>$\Omega +$和反射方程中的$H^2$都表示半球</li>
|
||
</ul>
|
||
<h4 id="帮助理解渲染方程"><a href="#帮助理解渲染方程" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>帮助理解渲染方程</h4>
|
||
<p>反射方程：</p>
|
||
<ul>
|
||
<li>对于一个点光源，反射方程描述Li进来经过BRDF反射到观察方向上去的能量</li>
|
||
</ul>
|
||
<p><img src="../../images/understanding_flection_equation1.png" alt=""></p>
|
||
<ul>
|
||
<li>如果有多个光源，就累加计算每个点光源光线到这个点反射到观测方向上的能量值</li>
|
||
</ul>
|
||
<p><img src="../../images/understanding_reflection_equation2.png" alt=""></p>
|
||
<ul>
|
||
<li>如果有一个面光源(一堆点光源的集合)，则将面光源上任意一个点的贡献积分起来</li>
|
||
</ul>
|
||
<p><img src="../../images/understanding_reflection_equation3.png" alt=""></p>
|
||
<p>渲染方程：</p>
|
||
<ul>
|
||
<li>在考虑其他物体反射过来的光时，可以将反射面视为光源，由于渲染方程假设所有方向都是向外的，所以从x点指向反射面就要变成负的</li>
|
||
</ul>
|
||
<p><img src="../../images/understanding_rendering_equation1.png" alt=""></p>
|
||
<p>该点向某一观察方向辐射出去的Radiance是依赖于其他点辐射出去的Radiance，即为递归过程</p>
|
||
<p>递归的另一用处：简化方程</p>
|
||
<p>在某个方向看向一点时，我们不知道看到的能量(Lr)、从其他反射到这一点的Radiance，但其他项都已知，可定义物体的不同材质(diffuse、gloss、specular)</p>
|
||
<p><img src="../../images/rendering_equation_simplify.png" alt=""></p>
|
||
<p>可利用数学上的一些简单表达式进行简化</p>
|
||
<p>$$I(u) = e(u) + \int {I(v) k(u,v)dv}$$</p>
|
||
<p>I: 从两个不同位置(u,v表示)辐射出去的Radiance，</p>
|
||
<p>e：着色点自己发出的能量在加上从其他物体表面反射来的Radiance反射到该着色点后有多少能量辐射到观察方向</p>
|
||
<p>$k(u,v)dv$ : 方程核心</p>
|
||
<p>进一步简化：</p>
|
||
<p>将BRDF和积分写成某种操作符(算子)后简化为下列式子，</p>
|
||
<p>$$L = E +KL$$</p>
|
||
<p>所有物体辐射出的所有能量 = 所有光源辐射出来的能量加上辐射出来的能量被反射后的能量</p>
|
||
<p>解渲染方程 ：</p>
|
||
<ul>
|
||
<li>将KL移至方程左侧，L写成单位矩阵*L的形式</li>
|
||
<li>将(I-k)移至右侧</li>
|
||
<li>计算(1-K)的逆即可解出L的值</li>
|
||
</ul>
|
||
<p>$$L = E + KL$$
|
||
$$IL - KL = E$$
|
||
$$(I - K)L = E$$
|
||
$$L = (I - K )^{-1}E$$</p>
|
||
<p>算子本身具有类似泰勒展开的性质</p>
|
||
<p>$$L = (I + K + K^2 + K^3 + \ldots)E$$
|
||
$$ L = E +KE+ K^2E +K^3E + \ldots $$</p>
|
||
<p>可看做：</p>
|
||
<p>光源直接辐射(E)，加上经过一次反射后的辐射(KE)，加上经过两次反射后的辐射(k^2E)</p>
|
||
<p>即分解了光线传播过程的弹射次数</p>
|
||
<h3 id="全局光照global-illumination"><a href="#全局光照global-illumination" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>全局光照(global illumination)</h3>
|
||
<p>光线弹射一次得到为直接光照，弹射两次及以上为间接光照，所有光线弹射次数的项加起来的结果为全局光照(直接光照+间接光照)</p>
|
||
<h4 id="实例-光栅化"><a href="#实例-光栅化" class="anchor-link"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" class="icon anchor-icon"><path d="M326.612 185.391c59.747 59.809 58.927 155.698.36 214.59-.11.12-.24.25-.36.37l-67.2 67.2c-59.27 59.27-155.699 59.262-214.96 0-59.27-59.26-59.27-155.7 0-214.96l37.106-37.106c9.84-9.84 26.786-3.3 27.294 10.606.648 17.722 3.826 35.527 9.69 52.721 1.986 5.822.567 12.262-3.783 16.612l-13.087 13.087c-28.026 28.026-28.905 73.66-1.155 101.96 28.024 28.579 74.086 28.749 102.325.51l67.2-67.19c28.191-28.191 28.073-73.757 0-101.83-3.701-3.694-7.429-6.564-10.341-8.569a16.037 16.037 0 0 1-6.947-12.606c-.396-10.567 3.348-21.456 11.698-29.806l21.054-21.055c5.521-5.521 14.182-6.199 20.584-1.731a152.482 152.482 0 0 1 20.522 17.197zM467.547 44.449c-59.261-59.262-155.69-59.27-214.96 0l-67.2 67.2c-.12.12-.25.25-.36.37-58.566 58.892-59.387 154.781.36 214.59a152.454 152.454 0 0 0 20.521 17.196c6.402 4.468 15.064 3.789 20.584-1.731l21.054-21.055c8.35-8.35 12.094-19.239 11.698-29.806a16.037 16.037 0 0 0-6.947-12.606c-2.912-2.005-6.64-4.875-10.341-8.569-28.073-28.073-28.191-73.639 0-101.83l67.2-67.19c28.239-28.239 74.3-28.069 102.325.51 27.75 28.3 26.872 73.934-1.155 101.96l-13.087 13.087c-4.35 4.35-5.769 10.79-3.783 16.612 5.864 17.194 9.042 34.999 9.69 52.721.509 13.906 17.454 20.446 27.294 10.606l37.106-37.106c59.271-59.259 59.271-155.699.001-214.959z"/></svg></a>实例-光栅化</h4>
|
||
<p>光栅化在已知着色点与光源位置的情况下便可以做着色，着色实际为直接光照</p>
|
||
<p>因此光栅化能表现的光线传播内容实际上只有零次和一次弹射(光源自己+直接光照)</p>
|
||
<ul>
|
||
<li>直接光照(光源能直接照射的地方有颜色，其余位置为黑的)</li>
|
||
</ul>
|
||
<p><img src="../../images/Direct_illumination_eg.png" alt=""></p>
|
||
<ul>
|
||
<li>一次间接光照(光弹射两次)</li>
|
||
</ul>
|
||
<p><img src="../../images/one-bounce_global_illumination_eg.png" alt=""></p>
|
||
<ul>
|
||
<li>两次间接光照(光弹射一次，两次，三次累积后的全局光照效果)</li>
|
||
</ul>
|
||
<p><img src="../../images/two-bounce_global_illumination_eg.png" alt=""></p>
|
||
<ul>
|
||
<li>四次间接光照(玻璃灯内部变亮，在弹射三次时，仅足够进入物体，不足以离开物体)(双层玻璃需要两次弹射进入，两次弹射离开)</li>
|
||
</ul>
|
||
<p><img src="../../images/four-bounce_global_illumination_eg.png" alt=""></p>
|
||
<p>8次弹射和16次弹射只会提高暗处亮度，难以感知到</p>
|
||
<p>在无限次数弹射下，亮度会收敛到某一个值上，不会有剧烈变化，也不会产生过曝</p>
|
||
<p>在相机的情况下，保持快门打开则会产生过曝现象，与辐射度量学中单位时间的条件相应，快门打开使积累能量的时间变长，亮度变亮</p>
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