Net Journal 4
Explanation 1: Brightness and occlusion
Among the unfavorable conditions in the actual application of image-matching technology, brightness and occlusion have the greatest impact. In CC, which is a common image-matching technology, pixels from two digital images are compared, and parts with a certain degree of brightness matching are identified as identical images. Thus, unfavorable conditions such as the use of a flashbulb or a change in the sun's position may cause variations in the brightness of images of the same object, and matching may not be performed. In Fig. 1-A (a doll), an experiment to make an image-processing robot search for and match the same part as the lower right image (the doll's head) was conducted. The face of the doll in the target image looks darker than the sample due to the use of a flashbulb. This difference in brightness could not be detected by CC or SSD, which indicated parts different from the sample. The increment sign correlation (ISC) developed by our graduate school can read the difference in brightness and specify an almost correct position. In Fig. 1-B (Japanese playing cards), ISC can identify the correct card even though there are parts covered with overlapping cards (occluded parts).
Explanation 2: Image matching by orientation code matching
When a snack container is close to the camera, some parts become shaded. While SSD cannot continue tracking the container as it fails to recognize the shaded parts, a method known as OCM (orientation code matching) can. This technique uses information on the direction of contrasts near the pixels, and can ensure robustness against local changes in brightness.