  Microorganisms such as bacteria and fungi play essential roles in many
application fields, like biotechnique, medical technique and industrial domain.
Microorganism counting techniques are crucial in microorganism analysis,
helping biologists and related researchers quantitatively analyze the
microorganisms and calculate their characteristics, such as biomass
concentration and biological activity. However, traditional microorganism
manual counting methods are time consuming and subjective, which cannot be
applied in large-scale applications. In order to improve this situation, image
analysis-based microorganism counting systems are developed since 1980s, which
consists of digital image processing, image segmentation, image classification
and so on. Moreover, image analysis-based microorganism counting methods are
efficient comparing with traditional plate counting methods. In this article,
we have studied the development of microorganism counting methods using digital
image analysis. Firstly, the microorganisms are grouped as bacteria and other
microorganisms. Then, the related articles are summarized based on image
segmentation methods. Each part of articles are reviewed by time periods.
Moreover, commonly used image processing methods for microorganism counting are
summarized and analyzed to find technological common points. More than 142
papers are summarized in this article. In conclusion, this article can be
referred to researchers to determine the development trend in microorganism
counting field and further analyze the potential applications
