**6. Conclusions**

In recent years, with the sharp increase in image data processing, the problem of realtime processing has become a limitation in classical image processing. An image component labeling algorithm is an important pre-processing operation in many image processing algorithms. However, in quantum image processing, component labeling algorithm has not been reported in extant literature. In this paper, we develop a quantum version of the image component labeling algorithm which makes full use of quantum parallelism. Firstly, the modified NEQR model is used to represent the information of binary image. Secondly, basic function circuits are prepared. Thirdly, the quantum circuits of parallel shrinking and label propagating are designed by using the basic function circuits. The purposed circuits can process information of all the pixels simultaneously, which can improve the efficiency of image preprocessing.

Quantum image processing applications have developed only in recent years. The results obtained in this paper could be used in more quantum image processing algorithms. In the future, we will be working to develop new quantum image analysis algorithms based on the quantum component labeling algorithm, especially in the fields of transportation, logistics, and robot navigation.

**Author Contributions:** Conceptualization, Y.L. and D.H; methodology, K.L.; software, D.H.; validation, Y.X.; writing—original draft preparation, Y.L.; writing—review and editing, D.H.; supervision, K.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors are thankful to the editor and the reviewers for their valuable comments and suggestions that helped to improve the quality of the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
