Reading Braille on aluminum can lids
Reverse vending machines are automated machines that utilize advanced technology to identify, sort, collect and process used beverage containers. Some markets with reverse vending systems have problems with imported used beverage cans from other countries. Tomra Systems ASA has developed a system for reading embossed dot patterns on the can lids for increased reliability of refund calculation. The text or symbols are embossed in the can’s lid when produced.
Rolled metal surfaces are difficult to image, especially so in space-restricted areas. Direct reflexes and surface texture blinds the camera, and make information contained on the metal surface illegible. This was solved by a now patented illumination strategy using multiple illumination sources to alleviate reflex problems. This makes the area of interest visible in at least one of the images.
Different symbols for identification were considered. Dot symbols were chosen as they will look the same from all positions, which simplify the analysis. This suggests using Braille codes, to the benefit for visually impaired.
The dots are left as brighter spots on the lid. First the lid is located as an ellipse in the image. The lids shape is used for correcting the perspective in the image. The Braille dots in the symbol are found and then read by comparing them with registered symbols in a database. The recognition is done regardless of rotation or scaling. Figure 1 shows typical images, and the detection of the lid and the Braille dots are marked out in figure 2.
If you are interested in more information please contact
Trine Kirkhus
.
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Figure 1: Images captured with the two illumination sources. |
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Figure 2 a) Braille dots found on the lid, marked with yellow dots. b) Braille template used for matching. |
