A pattern of a diffraction image depends on the particle shape, while the size of the pattern depends on the sectional area of the particle. In this work, the method to extract differences from the diffraction patterns due to different shapes of non-spherical particles was studied conceptually. In this respect, a radial segment (wedge) photo-detector was assumed as a detector. Diffraction patterns and intensity patterns detected by the radial segment detector were calculated for many kinds of two-dimensional shapes, corresponding to the projections of particles, as a circle, ellipses, triangles, quadrangles, other anonymous shapes, also shapes extracted from real phytoplanktons. From these detected light intensity patterns, we extracted (or define) two indexes: "circular index" and "peak number." It was shown that various shapes can be distinguished by means of two-dimensional mapping with these parameters. In addition, an applicability of a concentric detector was examined to estimate the particle size when the particle is non-spherical but is a single particle in the measurement. As a result, it was found that the circle equivalent diameter determined with usual scheme agreed well with the sectional area equivalent diameter of the original particle even in any cases of non-spherical samples. From these results, it was shown that the particle size and shape in wide range can be distinguished from the three-dimensional mapping with "circular index", "peak number" and "particle size".