前言由于胶片技术及设备的不断革新,促进了小尺寸影片(如16毫米、8毫米、超8毫米)的发展。与此同时,对光学印片机的精密性及胶片的清洁度提出了更高的要求。因为原底片上的脏点及划伤会转印到正片上而破坏画面,影响放映效果。通常,人们用PI比(即脏点大小与影象尺寸之比)来说明脏点与放映效果的关系。譬如一个0.05毫米的尘埃脏点,在35毫米胶片上的PI比为1:412;在16毫米胶片上为1:190;在超8毫米片子上则为1:105。若银幕上的画面宽为5.2米,这一粒子仅放大250倍, Preface Due to the continuous innovation of film technology and equipment, the development of small-sized films (such as 16mm, 8mm and 8mm) has been promoted. At the same time, the optical printer’s precision and film cleanliness put forward higher requirements. Because the original film on the dirty spots and scratches will be transferred to the positive and destroy the screen, affecting the screening effect. Generally, people use PI ratio (ie, the ratio of the size of the dirty spots to the size of the image) to illustrate the relationship between the dirty spots and the screening effect. For example, a 0.05 mm dusty spot with a PI ratio of 1: 412 on 35 mm film, 1: 190 on 16 mm film and 1: 105 on super 8 mm film. If the screen width of 5.2 meters, this particle only magnified 250 times,