Application of video image processing to a volcanic eruption was attempted, using video image archives of Aso volcano. As a result, continual flashings in the pale gray plume that appeared to be continual (5--6 times per second) and long-lived nature (more than 20--30 sec) were found. The speed of their propagation was very high, 200--300 m/sec. They are thought to be due to a phase change of H2O in the plume caused by volcanic pressure waves, but they cannot be recognized directly on normal images. The video image processing reported here will become increasingly more useful in the field of volcanology as the imaging technology is developed.