Rosenstein D S
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing 48824-1314, USA.
Vet Radiol Ultrasound. 1998 Jul-Aug;39(4):304-8. doi: 10.1111/j.1740-8261.1998.tb01610.x.
Image magnification is inherent in radiography. In digital fluoroscopy, the three components of magnification are geometric, electronic and photographic. In this study, the total magnification factor of a digital imaging system was determined by two methods, 1) comparison of measurements of a known object to its image and 2) calculation of geometric, electronic and photographic magnification from the imaging system specifications. Both methods were employed for various focal-film distances, image intensifier tube modes and laser printer formats. Results of these two methods were different due to the detrimental effect of penumbra on image quality with increasing magnification. If a radiographic image is to be used to approximate object size, then a technique should be used that will minimize magnification. In digital fluoroscopy this is achieved with the shortest object-film distance (assuming a fixed focal-object distance), largest image intensifier mode and greatest number of images per sheet of film.
影像放大是放射照相术固有的特性。在数字荧光透视中，放大的三个组成部分是几何放大、电子放大和摄影放大。在本研究中，数字成像系统的总放大倍数通过两种方法确定：1）将已知物体的测量值与其图像进行比较；2）根据成像系统规格计算几何放大、电子放大和摄影放大。这两种方法都应用于不同的焦-片距离、影像增强管模式和激光打印机格式。由于随着放大倍数增加半影对图像质量产生不利影响，这两种方法的结果有所不同。如果要用射线照相图像来近似物体大小，那么应采用能使放大倍数最小化的技术。在数字荧光透视中，这可通过最短的物体-胶片距离（假设焦-物距离固定）、最大的影像增强器模式以及每张胶片最多的图像数量来实现。
