Although some image programs such as Photoshop allow you to increase the resolution by entering in a higher value, it will not increase the quality of your image. This method relies on interpolating the image. In this method, the program estimates where to add information to the image in order to increase the resolution. Although it does increase the resolution, it does not produce the same level of quality as a picture scanned at the proper resolution from the beginning. Before scanning, you need to know what scanning method to use.
Line art is always black and white images with no shades of gray.
To avoid jagged edges, line art should be scanned with a resolution of at least 800 dpi. If you try to scan line art using the grayscale mode, the lines will appear blurry. For grayscale and color images, you need a resolution of twice the linescreen. It's also important that the item is scanned at the size at which it will be used in your document. For example, if you scan a picture at one size, but plan to enlarge it in your document, the resolution of the picture will decrease.