Depth estimation using light field question about a research paper

Hello everyone! I'm currently delving into an article on depth estimation using light fields captured by plenoptic cameras. I've encountered a bit of confusion when the article describes a particular figure as being "Gaussian in the x direction and a ridge in the u direction." I'm quite clear on what "Gaussian in the x direction" signifies, but I'm struggling to grasp the concept of a "ridge in u direction." Could someone kindly clarify what this means, particularly the "ridge in …

article cameras clear computervision fields figure hello light paper research research paper ridge