The scanned image data is the set of points storing brightness and color information. The density of these points is called "resolution" and the number of points (dots) within 1 inch is represented by "dpi." The resolution defines the fineness or roughness of the image. The higher the resolution (larger the number), the finer the image. The lower the resolution (smaller the number), the rougher the image.
You should set the scanning resolution according to the resolution of the final output device, for example, a display or printer.
Images for Display on a Monitor
For images for display on a monitor, scan them in 150dpi which is close to the resolution of the normal monitor.
Images for Printing
For images for printing by a printer, scan them in the resolution of the printer.
For example, select 600dpi if you print with the 600dpi black and white printer.
For the color printer, select the resolution which is half the resolution of the printer because the color is recreated with multiple inks. For example, select 300dpi if you print with the 600dpi color printer.
However, the higher the resolution, the longer the scanning time. Select the minimum resolution in accordance with the intended use.
Printing to Scale
For example, if you print an image by doubling its size, the actual resolution becomes half the scanned resolution. Therefore if the resolution of the original image is 300 dpi, the resolution of the doubled image becomes 150 dpi. If you then print the image on a 600-dpi color printer, the coarseness may stand out. In this case, scan the image at 600 dpi. Then when you double the image size, the resolution becomes 300 dpi, and the quality of the printed image should be satisfactory.
Conversely, if you reduce a scanned image in half before printing it, you only need to scan the image at half the desired resolution.
Resolution and Data Size
When you double the resolution, the data size of the scanned image becomes 4 times larger. If the data size is too large, the processing speed may drop significantly or a memory shortage may occur. Select the minimum resolution in accordance with the intended use.