Method and apparatus for watermarking film

公开了一种用于在生产时将数字水印图像预曝光到感光介质(140)上的印刷方法和装置(100)。对于曝光能量，该装置使用包括一个LED阵列的单色光源(60)。该LED是利用反射LCD阵列(91)对亮度进行空间调制的。可以对感光介质(140)进行校正以允许预曝光这种单色光，同时还避免了色调偏移和对比度损失。胶片上的曝光量可以通过以下方式来增加：使用部分帧照明、利用具有短脉冲周期和低占空比的高电流给LED输送脉冲、使用两个LCD设备(91、92)来利用两种偏振及分色组合两个具有略不同波长的LED阵列(60、61)。 A printing method and apparatus ( 100 ) for pre-exposing a digital watermark image onto a photosensitive medium ( 140 ) at the time of manufacture is disclosed. For exposure energy, the apparatus employs a single color light source ( 60 ) consisting of an array of LEDs. The LEDs are spatially modulated in intensity by means of a reflective LCD array ( 91 ). The photosensitive medium ( 140 ) may be compensated to allow such single color pre-exposure while avoiding hue shift and contrast loss. The exposure at the film may be increased by: employing partial frame illumination, pulsing the LEDs with high currents with short pulse durations and low duty cycles, employing two LCD devices ( 91, 92 ) to utilize both polarizations, and dichroically combining two LED ( 60, 61 ) arrays of slightly different wavelengths.