Image size is measured in horizontal and vertical dimensions as measured in pixels. For example, 640 X 480 means the image is 640 pixels across and 480 pixels high. (Please note that size can be a true recorded size or a computer enhanced size). While this measurement provides the size of the image, the resolution refers to the detail contained within the image and is listed as lines of resolution. These lines are the number of lines that can be individually differentiated within the image. The greater the number of lines, the more details that are identifiable in the image. An image recorded at a full 640 X 480 size may have a resolution up to 500 horizontal lines X 480 vertical lines, while an image size of 320 X 240 may have approximately 280 horizontal and 240 vertical lines of resolution. Also take into consideration that a DVR that records at 320 X 240 and then uses a computer formula to enhance the image to 640 X 480 is not increasing the resolution of the image - only the size. 320 X 240 (VHS quality, 640 X 240 (SVHS quality), and 640 X 480 (DVD quality) are all available from PSCS.