Method for detecting single postal covers and postal covers stuck together in a mail sorting machine
The method of detecting single postal items and multiple overlapping postal items in a postal sorting installation consists in analyzing images ( 5 ) representing postal items ( 6 ) viewed from in front, and in applying to each image an outline-extracting process ( 10 ) in order to recognize items ( 6 ) having an outline ( 10 ) of substantially constant height as being single items. In this method, the reliability with which single items is detected is improved, and the digital image used for analysis purposes can be the digital image which is also used for optical character recognition processing in the postal sorting installation.
1. A method of detecting single postal items and multiple overlapping postal items in a postal sorting installation, said method comprising a step of providing a height measurement of the postal items ( 6 ) and detecting a variation of the measured height indicative of multiple overlapping postal items, said method being characterized in that said step of providing a height measurement comprises:
acquiring an image ( 5 ) of each postal item viewed from in front into an address automatic recognition process,
applying to each image ( 5 ) an outline-extraction process ( 10 ) to extract an outline of each postal item; and
analyzing said outline to provide said height measurement of said postal items.
2. A method according to claim 1 , in which the outline extraction process comprises applying the Sobel operator or the Prewitt operator to the image.
3. A method according to claim 1 , in which if the outline analysis leads to the detection of a variation of height of the outline, data representing the height of said outline at various points of the outline are provided to a classifier (CL) to detect a multiple overlapping postal item.
4. A method according to claim 3 , in which the classifier is implemented in the form of a neural network.
5. A method according to claim 3 , in which the classifier uses a set of statistical descriptors or primitives to characterize the outline.
6. A method according to claim 1 , for a postal sorting installation including a device for rejecting multiple overlapping postal items, which method comprises counting the single postal items and the multiple overlapped postal items and deactivating rejection of multiple overlapping postal items when a first predetermined number (n 1 ref) of consecutive postal items are detected as being multiple overlapping postal items ( 6 , 6 ′), said rejection being reactivated when a second predetermined number (n 2 ref) of consecutive postal items are detected as being single postal items.