Resolution

Resolution

Q1:	What is interpolation?
A1:	Interpolation is a process that "invents" new pixels based on nearby pixels. It is used when you try to increase image resolution without changing the image's physical size . Some people call interpolation "fake resolution," because the results are not as good as if you had scanned the image at a higher resolution. In general, I would avoid it if possible, with a couple of exceptions: If you are scanning (or have scanned) line art, interpolation does not seem to have as noticeable of an effect. If the image does not have fine detail (e.g., a cloudy sky), then the lack of sharpness will not be as much of an issue.
Q2:	Why does my image print so much smaller than it looks onscreen? When I look at my image onscreen, it looks very large, but when I print it, it is much smaller. Why?
A2:	When you view images onscreen, the resolution of the image is affecting the way it displays. For example, if you scanned a 3x3" photo at 300 ppi, it would look approximately four times larger onscreen, since the resolution of your monitor is roughly 72 ppi. The image itself is still a 3" square, and that's how large it will print. The higher resolution of the scan lets you zoom in and display the pixels at the full resolution, but the size you see onscreen is not the print size. Try looking under the View menu and selecting Print Size; that will show a more accurate preview of how large the image will print.
Q3:	Why did the size of a selection change when I dragged it into another document? I dragged-and-dropped part of an image into another document, but now the pixels I dragged seem much bigger (or smaller). What gives?
A3:	This happens when the resolution of the two images is not the same. For example, if you select some pixels in an image that is 200 ppi, and then drag them into a second document that is 100 ppi, the dragged pixels will appear twice as big in the new document, as you are going from higher to lower resolution. The opposite would happen if you drag from lower to higher resolution. The solution? Either ensure that the two documents share the same resolution or make sure you are aware of the difference in resolution, so you are not surprised by the result.