Photoshop Terms
Pixel dimensions: how many pixels wide by how many pixels high
Document size or print size: the size the image would be if printed
File size: how much space the file occupies on your hard disk
Resampling, or interpolation: The process of adding (or subtracting) pixels from an image. The resampling or interpolation process of removing unnecessary pixels is also known as down-sampling. The resampling or interpolation process of making up new pixels is also known as up-sampling.
Scratch disk: actual physical space on a hard drive that Photoshop uses if it runs out of RAM in which to do its calculations. It’s not enough in Photoshop to have plenty of RAM; you also need to have a fair amount of empty hard drive space as well.
LPI (lines per inch) LPI refers to the screen frequency of the halftone that will be used to translate your image from pixels into something that can be printed on a press (CMYK mode.) A halftone converts a continuous tone image into a pattern of cyan, magenta, yellow, and black dots so that the inked printing plates on a press can reproduce it. For an image that will be reproduced on a press, the resolution of the image (ppi) should be 1.5x to 2x the halftone line screen (lpi). So for a good quality magazine that is using a halftone line screen of 150 lpi, the resolution of your digital image should be between 225 and 300 ppi and the document or print size should be set to whatever size you want it to be reproduced at. To err on the side of best quality, go for the 2x value. You can also think of it by using this formula: LPI x 2 = PPI
