Camera Raw is both the engine that translates your raw captures into color images, and the user interface that lets you control that translation. The role that Camera Raw plays when the user interface is exposed is fairly obvious: its role behind the scenes is less so.
One of the key roles that Camera Raw plays is to generate the thumbnails and previews you see in Bridge. When you first point Bridge at a folder full of new raw images, you may see, typically for a few seconds, the camera-generated thumbnails. But Camera Raw immediately goes to work behind the scenes, generating the large, high-quality previews and downsampling them to produce new thumbnails.
Camera Raw also has the interesting property of being shared by Bridge and Photoshop, which opens up some new workflow possibilities. You can, for example, edit images in Camera Raw hosted by Bridge, and hand off the processing of the raw image out to a saved RGB image file to Camera Raw running in Photoshop while you continue to edit more images in Camera Raw hosted by Bridge.
Camera Raw Defaults
The role of Camera Raw's default settings in generating Bridge's thumbnails and previews is pretty straightforward. Unless and until you tell it to do otherwise, Camera Raw uses its default settings to build thumbnails and previews for images that Bridge hasn't seen before.
The defaults aren't sacred, or "objectively correct," or "as shot"—they're simply one arbitrary interpretation of the raw image. There's no such thing as an "as shot" interpretation any more than there's a single correct way of printing a negative. One of the most common complaints I hear about Camera Raw is that the images don't look like the in-camera JPEGs or the default conversions from the camera vendors' raw converters. Invariably, those making the complaints haven't bothered to actually use Camera Raw's controls—they just use the defaults.
Part of the problem is likely that Camera Raw gives you access to all the data the camera captured. Many proprietary raw converters bury shadow noise by applying a strong contrast curve that maps most of the shadow data to black. A good many also boost the saturation. Camera Raw's default interpretations tend to be conservative by comparison, with flatter contrast and more open shadows. I prefer this approach because it makes it easier to see just what usable data the image contains, but that's only my personal preference. More importantly, Camera Raw offers sufficient control over the interpretation of the image that, with a very little practice, you can get just about any "look" you want.
So if you consistently find that Camera Raw's default settings produce images that are too dark, too light, too flat, or too contrasty for your taste, change them! It only takes a very few minutes. I'll discuss Camera Raw's controls, and how to use them—including changing the defaults—in the next chapter, Camera Raw Controls.