For 16 million color images, there are 24 bits of data stored in each pixel. Like dpi, raising the bit depth also increases your file size, but gives you more colors, and better color gradations. Any level of gray will be converted to black or to white. Halftone -simulates halftone screens printing screen. In older newsprint you could see small dots of varying sizes creating the illusion of gray scale.
Comic books use larger screen dots.
Photo-Gray Scale and Continuous Tone Are all equivalent. However, being the best has its costs. This scan type also generates the largest file sizes. The program in which your final image will used affects the file format you will save your file as. The EPS file from the HP IIcx ScanJet is inconsistent with Adobe's EPS rasterizer.