The above description from Collins English Dictionary should help us understand what interpolation is all about, especially point 3. When a flatbed scanner converts light into electrical current, converts the current values into digital values and then starts to construct a bitmapped array of information that it will send to the scanning software as a picture, interpolation comes into play. When using a digital camera to capture events for image display etc., depending on the resolution nominated for the camera to save the images to its memory, interpolation again comes into play and so on it goes.
Interpolation is used in Painting programs all the time.
The lens focuses the image onto a fixed array of CCDs and up to this point nothing changes from scan to scan - always the same size and resolution. Once digitised the information is reconstructed to the dimensions requested by the operator via the scanning software - it is interpolated. With the following diagrams I will try to explain interpolation so that you can appreciate its importance and realise why you should test for the best options when scanning and manipulating bitmap images. A bitmap image contains an array of pixels - rows and columns. As a simple example suppose the operators request equates to double the resolution of the CCD resolution for an image that will output at the same size of the original copy.