Differentiable rendering methods promise the ability to optimize various parameters of 3d scenes to achieve a desired result. However, lighting design has so far received little attention in this field. In this paper, we introduce a method that enables continuous optimization of the arrangement of luminaires in a 3d scene via differentiable light tracing. Our experiments show two major issues when attempting to apply existing methods from differentiable path tracing to this problem: first, many rendering methods produce images, which restricts the ability of a designer to define lighting objectives to image space. Second, most previous methods are designed for scene geometry or material optimization and have not been extensively tested for the case of optimizing light sources. Currently available differentiable ray-tracing methods do not provide satisfactory performance, even on fairly basic test cases in our experience. In this paper, we propose a novel adjoint light tracing method that overcomes these challenges and enables gradient-based lighting design optimization in a view-independent (camera-free) way. Thus, we allow the user to paint illumination targets directly onto the 3d scene or use existing baked illumination data (e.g., light maps). Using modern ray-tracing hardware, we achieve interactive performance. We find light tracing advantageous over path tracing in this setting, as it naturally handles irregular geometry, resulting in less noise and improved optimization convergence. We compare our adjoint gradients to state-of-the-art image-based differentiable rendering methods. We also demonstrate that our gradient data works with various common optimization algorithms, providing good convergence behaviour. Qualitative comparisons with real-world scenes underline the practical applicability of our method.

翻译：可微渲染方法有望实现三维场景中各种参数的优化以达成预期效果。然而，照明设计在该领域中至今未受到足够重视。本文提出一种通过可微光线追踪实现三维场景中灯具布局连续优化的方法。实验表明，将现有可微路径追踪方法应用于该问题时存在两大难题：其一，多数渲染方法生成图像，这限制了设计师对照明目标的定义范围仅局限于图像空间；其二，现有方法主要面向场景几何或材质优化，未充分验证光源优化场景。目前可用的可微光线追踪方法即便在基础测试案例中也未能提供令人满意的性能。本文提出的新型伴随光线追踪方法克服了这些挑战，实现了基于梯度的视点无关（无相机）照明设计优化。由此，用户可直接在三维场景中绘制照明目标，或利用现有烘焙照明数据（如光照贴图）。借助现代光线追踪硬件，我们实现了交互式性能。在此场景中，我们发现光线追踪相较于路径追踪具有优势——其天然适配不规则几何结构，能降低噪声并提升优化收敛性。我们将伴随梯度与当前最优的基于图像的可微渲染方法进行对比，同时证明梯度数据可适配多种通用优化算法，展现出良好的收敛特性。与真实场景的定性比较验证了本方法的实际应用价值。