>55 Creating Colors
      There are two ways to create colors in a photograph. One method, called additive, starts with three basic colors and adds them together to produce some other colors. The second method, called subtractive, starts with white light (a mixture of all colors in the spectrum) and by taking away some or all other colors leaves the one desired.
      In the additive method separate colored lights are combined to produce various other colors. The three additive primary colors are green, red and blue (each proportions, about one third of the wavelengths in the total spectrum). Mixed in varying proportions, they can produce all colors. Green and red light mix to produce yellow, red and blue light mix to produce magenta, green and blue mix to produce cyan. When equal parts of all three of these primary colored beams of light overlap, the mixture appears white to the eye.
      In the subtractive process, colors are produced when dye (as in paint or color photographic materials) absorbs some wavelengths and so passes on only part of the spectrum. The subtractive primaries are cyan (a blulish green), magenta (a purplish pink), and yellow; these are the pigments or dyes that absorb red, green and blue wavelengths, respectively, thus subtracting them from white light. These dye colors are the complementary colors to the three additive primaries of red, green and blue. Properly combined, the subtractive primaries can absorb all colors of light, producing black. But, mixed in varying proportions they too can produce any color in the spectrum.
      Whether a particular color is obtained by adding colored lights together or by subtracting some light from the total spectrum, the result looks the same to the eye. The additive process was employed for early color photography. But the subtractive method, while requiring complex chemical techniques, has turned out to be more practical and is the basis of all modern color films.

      创造颜色
      有两种方法可以使照片具有色彩。 一种叫加色法，通过把三种基本颜色相叠 加以产生其它色彩。 另一种叫减色法，通过去除白色(其实是光谱中所有颜色相混合的结果) 中的某些或其它所有色彩而把所需的色彩留下来。 在加色法中，不同颜色的光线混合以产 生其它各种色彩。 加色法三原色是绿、红和蓝(其中每一种占据总光谱中三分之一的波长)。 这三种色彩以不同比例相叠加可以产生所有色彩。 绿光和红光叠加可产生黄色，红光与蓝 光叠加可产生品红色，绿光与蓝光叠加可产生青绿色。 当这三种原色光以相同比例叠加时， 眼睛所见的就成为白色。 而在减色法中，染料(比如在绘画颜料或彩色照相材料中)吸收了 部分波长而只允许分光谱通过，从而产生各种色彩。 减色法三原色是青绿色、品红(略带紫 色的粉红色)和黄色； 也就是可分别吸收红光、绿光和蓝光的色料或染料，从而去除白色光 中的这些色彩。这些染料色是加色法的三原色红、绿、蓝的相互补充。 适当组合时，减色 法三原色能吸收光线中的所有色彩，产生黑色。 但当它们以不同的比例叠加时，也能产生 光谱中所有颜色。 不论某种颜色是通过把不同色彩的光线叠加还是把光谱中某些颜色的光 去除掉而产生的，它的视觉效果是一样的。 早期彩色摄影采用加色法。 但减色法尽管需要 复杂的化学技术，最终比前者更加实用，并成为现代彩色电影的基础。
>56 The Organic Foods
      Are organically grown foods the best food choices? The advantages claimed for such foods over conventionally grown and marketed food products are now being debated. Advocates of organic foods -- a term whose meaning varies greatly -- frequently proclaim that such products are safer and more nutritious than others.
      The growing interest of consumers in the safety and nutritional quality of the typical North American diet is a welcome development. However, much of this interest has been sparked by sweeping claims that the food supply is unsafe or inadequate in meeting nutritional needs. Although most of these claims are not supported by scientific evidence, the preponderance of written material advancing such claims makes it difficult for the general public to separate fact from fiction. As a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore.
      Almost daily the public is besieged by claims for "no-aging" diets, new vitamins and other wonder foods. There are numerous unsubstantiated reports that natural vitamins are superior to synthetic ones, that fertilized eggs are nutritionally superior to unfertilized eggs, that untreated grains are better than fumigated grains and the like.
      One thing that most organically grown food products seem to have in common is that they cost more than conventionally grown foods. But in many cases consumers are misled if they believe organic foods can maintain health and provide better nutritional quality than conventionally grown foods. So there is real cause for concern if consumers particularly those with limited incomes, distrust the regular food supply and buy only expensive organic foods instead.

      绿色食品
      绿色食品是最佳食物吗?有人认为绿色食品比通过常规方式生产和销售的食品 有更多的优越性，然而现在却有人对此提出异议。 绿色食品--这一词的用法非常不统一-- 支持者往往声称绿色食品比其它食品更安全，营养价值更高。 北美的消费者们越来越关注 他们的日常饮食是否安全和有营养。 这一发展趋势是好的。 然而这种关注多半是由一些武 断的说法引起的，即食物供应不安全或不能提供足够的营养。 尽管这些说法多数未被科学 证实，但是由于大量文章支持这一观点，使得普通群众难辨真伪。 因此那些认为只食用绿 色食品就能防治疾病或增进健康的观点便广为人知，并导致一些不科学的做法和习惯。 公 众几乎每天都被"抗衰老"食品、新型维生素以及其它具有神奇功效的食物广告所包围。 声 称天然维生素优于人造维生素，受精蛋比未受精蛋的营养价值更高，未经薰蒸消毒处理的谷 物比经过处理的好等等诸如此类的报道屡见不鲜，但没有一篇是经过证实的。 大多数绿色 食品有一共同点，即它们的价格高于以常规方式种植的食物。 但在许多情况下，如果消费 者认为绿色食品能预防疾病且营养价值高于以常规方式生产的食品，那么他们被误导了。如 果消费者们，尤其是那些收入有限的消费者们，怀疑传统食品而只购买更昂贵的绿色食品， 那就值得担忧了。