Accurate environment maps are a key component for rendering photorealistic outdoor scenes with coherent illumination. They enable captivating visual arts, immersive virtual reality, and a wide range of engineering and scientific applications. Recent works have extended sky-models to be more comprehensive and inclusive of cloud formations but, as we demonstrate, existing methods fall short in faithfully recreating natural skies. Though in recent years the visual quality of DNN-generated High Dynamic Range Imagery (HDRI) has greatly improved, the environment maps generated by DNN sky-models do not re-light scenes with the same tones, shadows, and illumination as physically captured HDR imagery. In this work, we demonstrate progress in HDR literature to be tangential to sky-modelling as current works cannot support both photorealism and the 22 f-stops required for the Full Dynamic Range (FDR) of outdoor illumination. We achieve this by proposing AllSky, a flexible all-weather sky-model learned directly from physically captured HDRI which we leverage to study the input modalities, tonemapping, conditioning, and evaluation of sky-models. Per user-controlled positioning of the sun and cloud formations, AllSky expands on current functionality by allowing for intuitive user control over environment maps and achieves state-of-the-art sky-model performance. Through our proposed evaluation, we demonstrate existing DNN sky-models are not interchangeable with physically captured HDRI or parametric sky-models, with current limitations being prohibitive of scalability and accurate illumination in downstream applications

翻译：精确的环境贴图是实现户外场景逼真渲染与连贯照明的关键要素，它们支撑着引人入胜的视觉艺术、沉浸式虚拟现实以及广泛的工程与科学应用。近期研究扩展了天空模型以更全面地涵盖云层形态，但如本文所示，现有方法在忠实还原自然天空方面仍存在不足。尽管近年来基于深度神经网络生成的高动态范围图像在视觉质量上已有显著提升，但由DNN天空模型生成的环境贴图在场景重照明时，其色调、阴影与光照效果仍无法与物理捕获的HDR影像相媲美。本研究指出，当前HDR领域进展与天空建模目标存在偏离，现有工作无法同时满足照片级真实感与户外照明全动态范围所需的22档光圈动态范围要求。为此，我们提出AllSky——一种直接从物理捕获的HDR影像学习的灵活全天候天空模型，并借此系统探究天空模型的输入模态、色调映射、条件控制及评估方法。通过用户对太阳位置与云层形态的自主调控，AllSky在现有功能基础上实现了对环境贴图的直观用户控制，并取得了最先进的天空模型性能。基于我们提出的评估体系，本文论证了现有DNN天空模型既无法替代物理捕获的HDR影像，也无法取代参数化天空模型，其当前局限性严重制约了下游应用的可扩展性与精确照明效果。