  The capacity of automatically modeling photographic composition is valuable
for many real-world machine vision applications such as digital photography,
image retrieval, image understanding, and image aesthetics assessment. The
triangle technique is among those indispensable composition methods on which
professional photographers often rely. This paper proposes a system that can
identify prominent triangle arrangements in two major categories of
photographs: natural or urban scenes, and portraits. For the natural or urban
scene pictures, the focus is on the effect of linear perspective. For
portraits, we carefully examine the positioning of human subjects in a photo.
We show that line analysis is highly advantageous for modeling composition in
both categories. Based on the detected triangles, new mathematical descriptors
for composition are formulated and used to retrieve similar images. Leveraging
the rich source of high aesthetics photos online, similar approaches can
potentially be incorporated in future smart cameras to enhance a person's photo
composition skills.
