B&W photography when using digital capture is a rendering process ... the sensor
always captures a full spectrum image, how you render it to a finished photograph is all that separates "shooting in color" vs B&W.
With some cameras, you can set the camera to automatically render a B&W image for you. Depending upon the camera, you have some control over what settings it uses to do that and the results might be satisfactory to you. But once done what you have from the camera are JPEG images which have lost a great deal of information, which makes further processing much more restrictive.
Who cares if the results are satisfactory out of the camera? ;-) If the camera's display shows the B&W rendering, it might aid you in making decisions about what to photograph. Or might not.
For my B&W, I capture in RAW format and do the rendering in image processing. My eyes are used to seeing a color world through the viewfinder and selectively tell me what is there in B&W, so I don't find a B&W rendering in camera very useful. With the RAW data, I can work both color and B&W renderings of a scene, a little bit of post-visualization, and see where it takes me as I work with it. With the RAW data, I can apply traditional B&W filtering to the image data to adjust and separate gray tones of differently colored things, push the rendering around with a great deal of control and finesse.
The Leica Digilux3 (and it's L1 sibling) have a fairly versatile B&W in-camera rendering engine for JPEGs. And save the full RAW data as well when you turn on the RAW capture facility. If you turn on the B&W rendering, that's what shows on the LCD in Live View while the optical viewfinder shows the normal color view of a scene. So it becomes the best of both worlds: you can capture both a tailored B&W JPEG image AND the full RAW dataset, and you can view normally or with a B&W translation on the image per your B&W rendering setup. It's amazing how versatile this camera is... !
Godfrey
http://www.gdgphoto.com
Great Egret - Guadalupe River Park 2007
Panasonic L1 + Nikkor 20mm f/3.5 AI