The extremes are referred to as the dynamic range . Film doesn't have anywhere near the dynamic range of nature, so it's always a struggle to accurately capture a scene on film. It's like trying to squeeze one of those coiled snakes back into the can after you've taken the lid off to let it pop out. Ansel Adams Zone System was developed to make this easier with black and white film, but color film can't be manipulated in the same way. This is one of the reasons that it's better to scan slides or negatives then prints.
Display screens have a dynamic range closer to slides than to prints.
That means that when you scan images for the Web, you need to be sure you capture the full dynamic range. How much dynamic range you can capture depends on its ability of the scanner's ability to register tonal values ranging from pure white to pure black. It must also be able to accurately map the tones on the original to tones on the digital image. If the scanner doesn't have enough tonal range, details will be lost in shadow areas, highlights, or both. Common flatbed scanners typically register values from about 0.0 to 2.4.