数字图像处理3rd - Chapter 1 - 2

1.2 The Origins of Digital Image Processing

1.2 数字图像处理的起源

One of the first applications of digital images was in the newspaper industry, when pictures were first sent by submarine cable between London and New York. Introduction of the Bartlane cable picture transmission system in the early 1920s reduced the time required to transport a picture across the Atlantic from more than a week to less than three hours. Specialized printing equipment coded pictures for cable transmission and then reconstructed them at the receiving end. Figure 1.1 was transmitted in this way and reproduced on a telegraph printer fitted with typefaces simulating a halftone pattern.

数字图像的最早应用之一是在报业中，当时图片首次通过海底电缆在伦敦和纽约之间发送。20世纪20年代初引进的Bartlane电缆图片传输系统将横跨大西洋的图片传输时间从一个多星期缩短到不到三个小时。专门的印刷设备为电缆传输的图片进行编码，然后在接收端进行重组。图1.1就是以这种方式传输的，并在装有模拟半色调图案的字体的电报打印机上进行重印。

Some of the initial problems in improving the visual quality of these early digital pictures were related to the selection of printing procedures and the distribution of intensity levels. The printing method used to obtain Fig. 1.1 was abandoned toward the end of 1921 in favor of a technique based on photographic reproduction made from tapes perforated at the telegraph receiving terminal. Figure 1.2 shows an image obtained using this method. The improvements over Fig. 1.1 are evident, both in tonal quality and in resolution.

在改善这些早期数字图片的视觉质量方面，最初的一些问题与印刷工艺的选择和亮度值的分布有关。用于获得图1.1的印刷方法在1921年底被放弃，转而采用一种新的摄影图像复制的技术，在电报接收终端使用打孔磁带。图1.2显示了使用这种方法获得的图像。与图1.1相比，无论是色调质量还是分辨率，都有明显的改进。

FIGURE 1.1 A digital picture produced in 1921 from a coded tape by a telegraph printer with special type faces. (McFarlane.)  

图1.1 1921年，由一台带有特殊字体的电报打印机根据编码纸带制作的数字图片。

FIGURE 1.2 A digital picture made in 1922 from a tape punched after the signals had crossed the Atlantic twice. (McFarlane.)

图1.2 1922年用信号两次穿越大西洋后的穿孔纸带制作的数字图片。

The early Bartlane systems were capable of coding images in five distinct levels of gray. This capability was increased to 15 levels in 1929. Figure 1.3 is typical of the type of images that could be obtained using the 15-tone equipment. During this period, introduction of a system for developing a film plate via light beams that were modulated by the coded picture tape improved the reproduction process considerably.

早期的Bartlane系统能够对图像进行五种不同灰度的编码。这种能力在1929年增加到15级。图1.3是使用15级色调设备可以获得的典型图像类型。在这一时期，引入了一个通过光束显影的系统，该光束由图像的编码纸带调制，极大地改善了复制过程。