本文是关于中国图像工程的年度文献综述系列之二十七。为了使国内广大从事图像工程研究和图像技术应用的科技人员能够较全面地了解国内图像工程研究和发展的现状，能够有针对性地查询有关文献，且向期刊编者和作者提供有用的参考，对2021年度图像工程相关文献进行了统计和分析。具体从国内15种有关图像工程重要中文期刊在2021年发行的所有154期上所发表的学术研究和技术应用文献(共2958篇)中，选取出所有属于图像工程领域的文献(共833篇)，并根据各文献的主要内容将其分别归入图像处理、图像分析、图像理解、技术应用和综述评论5个大类，然后进一步分入23个专业小类(与前16年相同)，并在此基础上分别进行了各期刊各类文献的统计和分析。根据对2021年统计数据的分析可以看出：图像分析方向当前得到了最多的关注，其中目标检测和识别、图像分割和边缘检测、人体生物特征提取和验证等都是研究的焦点。另外，遥感、雷达、声呐、测绘以及生物、医学等领域的图像技术开发和应用最为活跃。总的来说，中国图像工程在2021年的研究深度和广度还在继续提高和扩大，仍保持了快速发展的势头。综合27年的统计数据还为读者提供了更全面和更可信的各个研究方向发展趋势的信息。

This is the 27th annual survey series of bibliographies on image engineering in China. This statistic and analysis study aims to capture the up-to-date development of image engineering in China, provide a targeted means of literature searching facility for readers working in related areas, and supply a useful recommendation for the editors of journals and potential authors of papers. Specifically, considering the wide distribution of related publications in China, all references (833) on image engineering research and technique are selected carefully from the research papers (2 958 in total) published in all issues (154) of a set of 15 Chinese journals. These 15 journals are considered important, in which papers concerning image engineering have higher quality and are relatively concentrated. The selected references are initially classified into five categories (image processing, image analysis, image understanding, technique application, and survey) and then into 23 specialized classes in accordance with their main contents (same as the last 15 years). Analysis and discussions about the statistics of the results of classifications by journal and by category are also presented. Analysis on the statistics in 2020 shows that image analysis is receiving the most attention, in which the focuses are mainly on object detection and recognition, image segmentation and edge detection, as well as human biometrics detection and identification. In addition, the studies and applications of image technology in various areas, such as remote sensing, radar, sonar and mapping, as well as biology and medicine are continuously active. In conclusion, this work shows a general and up-to-date picture of the various continuing progresses, either for depth or for width, of image engineering in China in 2021. The statistics for 27 years also provide readers with more comprehensive and credible information on the development trends of various research directions.