Abstract: In order to provide an accurate sort into many different classes, objects are dropped through a viewing zone and viewed in the same instant by a number of viewers. Each viewer provides electronic signals representative of three basic shape features, namely blockiness, symmetry and convex hull deviance, together with a total count of edge-breakthroughs. For each basic shape feature, the maximum, minimum and mean are obtained for all the viewers, except the minimum convex hull deviance signal. These signals, together with the edge-breakthrough count, are each subjected to a linear transformation to provide a normalized shape parameter which is then assigned a value of 0 to 15 for each class being sorted on the basis of the expected occurrence of that parameter in that class. Each pair of secondary shape parameters so determined is used to derive from a respective table a decision value. The shape class of the object is ascertained on the basis of a majority vote for all the shape decision values.

Abstract: A rapid succession of objects such as sweets are sorted according to shape by being fed through a viewing zone, flash illuminated in the viewing zone, and viewed by a number of fixed electronic viewers spaced in one plane around the viewing zone through just under 180.degree., the edges of the images produced by the viewers being examined for approximation to a spherical shape, approximation to symmetry and reentrants, and one of a number of air jet nozzles being thereby automatically energised to direct the object into an appropriate bin.

Abstract: The color of gemstones or the like is assessed by projecting light onto the stone, using an interrupting member to regularly interrupt the path of the light shortly before it reaches the stone, the member having a normally white, diffusing interrupting surface, and using a detector for detecting the color of the light coming from the gemstone and from the interrupting surface of the interrupting member. Preferably, the stone is mounted in a chamber having normally white, diffusing internal walls and the diffusing interrupting surface is within the chamber.