http://www.bluecandy.typepad.com/my_weblog/
黑白照片的原则

If you happen to be working with flat light, pay   attention to the tones in your desired image.   A great black and white photo has a full range of tones from light to dark, without clipping either end of the spectrum.   You do not want to "blow out" the highlights of an image, which is when the lightest parts of an image have lost all detail.   (Highlight values over 255 are considered completely blown - you can check this with the eyedropper.)   This is especially tricky when shooting digital.   Below is an example of a blown out image...see how the light parts of the image are way too bright and detail is missing?
曝光过度 丢失细节不可取



错啦，上面应该是这图

The same goes for blocking the shadows (where detail is lost in the blacks).   And don't forget about the midtones!   Here is an example of the same photo that is missing a nice midtone range...even though the whites and blacks are where they should be, the midtones leave the photo with a lack of tonal depth.
同样不可丢失暗部细节


暗部 中间灰度 高光要自然过渡，如果缺乏对比，全图只有灰色则会图像会平淡模糊没有光彩，所以要有过渡与对比。



As you can probably tell by looking through my portfolio, I adore black and white images.   And I am quite picky (obsessed, maybe?!) about how they are processed!   Here is my final processing on the image...after using various curves, levels, contrast, and channel mixer layers and adjustments.
通过各种曲线，均衡，对比以及通道混合气来调整对象。