What you see on your monitor, even if the monitor is perfectly calibrated, can be deceptive. What may look good on screen may have serious technical shortfalls that become evident later, especially when you go to print. Let's look at the various tools Lightroom offers to evaluate your images.
Lightroom's tonal distribution and color evaluation tools include a histogram, over/under exposure warnings, and a color tool for taking precise color readings.
Using the Histogram
Lightroom's histogram graphically displays the 8-bit Red, Green, and Blue (RGB) values of your selected image. In the case of a RAW file, the histogram is not a reflection of the actual RAW data (which is grayscale and linear), but a reflection of the processed RGB data with nonlinear tone-mapping applied.
The histogram updates in real time to reflect changes you make to the white balance or tonal distribution. As you'll see later in the chapter, distribution of the tonal values can be made directly from the histogram or from other panes in the right panel. The Lightroom histogram is much more accurate than the one associated with your digital camera, so don't be surprised to see a difference.
Note the image in Figure 5-1. It's fairly intuitive to figure out what the colors in the histogram represent. Gray represents pixels in all three channels: red, green, and blue. Red represents red pixels, green represents green pixels, and blue represents blue pixels. Cyan represents ...