University of California, Berkeley, Berkeley, CA, USA.
Institut Jean Nicod, ENS, EHESS, CNRS, PSL University, Paris, France.
J Vis. 2023 Aug 1;23(8):13. doi: 10.1167/jov.23.8.13.
For more than 2000 years, artists have exploited cast shadows to influence how objects appear to be positioned in a scene. A contact cast shadow can anchor an object to the ground and a detached cast shadow can make an object appear to float. However, there is a period of approximately 1000 years when there were virtually no cast shadows in art. How were states of contact versus floating depicted by artists without cast shadows? Here, we survey various techniques used by artists to anchor relative position with and without cast shadows. We then conduct experimental tests of the hypothesized surface attraction principles that underlie these techniques. In the absence of cast shadows, an object (a wooden box) was often seen as resting on a surface as long as that surface offered information about ground orientation and support (a tiled floor). When the ground surface was ambiguous and cloud-like (1/f noise), the box was more likely to be seen to float. The presence of cast shadows made the box appear to contact the ground whether it was well-defined or ambiguous. Both shadows and surface support also increased the accuracy with which participants detected when the box was tilted up from the ground. These results indicate that artists long ago discovered the important power of support relationships to anchor objects to surfaces in the absence of shadows.
两千多年来，艺术家们一直利用投影来影响物体在场景中的位置。接触投影可以将物体固定在地面上，而分离投影可以使物体看起来漂浮。然而，有大约 1000 年的时间，艺术中几乎没有投影。那么，没有投影的艺术家们是如何描绘物体的接触状态和漂浮状态的呢？在这里，我们调查了艺术家们用来在有和没有投影的情况下固定相对位置的各种技术。然后，我们对这些技术所依据的假设表面吸引力原理进行了实验测试。在没有投影的情况下，只要表面提供有关地面方向和支撑的信息（例如瓷砖地板），一个物体（一个木制盒子）通常被视为放置在表面上。当地面表面模糊不清且呈云状（1/f 噪声）时，盒子更有可能被视为漂浮。即使投影的盒子的边界是清晰的还是模糊的，投影都会使盒子看起来与地面接触。投影和表面支撑都提高了参与者检测盒子从地面倾斜的准确性。这些结果表明，艺术家很久以前就发现了支撑关系的重要作用，它可以在没有投影的情况下将物体固定在表面上。
