Portable document scanner and much more
As useful and convenient as these devices are, they simply can't compare with larger models in terms of the clarity of the image. Nevertheless, they are sufficient for most casual uses, and their small size and portability makes up for any deficiency in image resolution. If you do want to get a better quality image, check for the dots per inch or dpi of the particular portable scanner that you are considering. Make sure to offers at least 48 bit depth image quality if you're particularly concerned about getting the best images possible. For tasks that involve simply scanning pages of text however, you should be able to make do with a model that offers only eight bits.