Video display accessory used to enhance the picture quality of a video image by combining the two interlaced fields (grouping of all the odd or all the even lines that make up a complete image; two fields make a frame or a complete image) and progressively displaying complete frames instead of fields (displaying all the odd and even lines generated in order one, two, three, etc.). nterlaced video works by displaying two fields for every frame. The first field displays all the odd lines of a complete video image (one, three, five, seven, etc.). The second field displays the even lines (two, four, six, eight, etc.). Thus, only half the picture is actually displayed every 1/60 second creating a full frame 30 times per second. ine doublers work by combining the odd and even lines of each field and creating full frames out of the fields. This effectively doubles the lines in a given field hence the term line doubling. Instead of an interlaced image, the line doubler combines the fields and produces a progressive scan image that paints every line in the picture in order (one, two, three, four, etc.). Each doubled field, essentially a complete frame, is then projected 60 times per second. The result, when done properly, is an image with much greater detail and clarity than a traditional, interlaced video image. ine doublers, however, are very complex and expensive. They must contain circuitry to save fields and combine them in the proper way to create progressive, doubled fields. This task is difficult enough by itself, but the nature of interlaced fields creates additional difficulties. Often the fields containing the odd lines and those containing the even lines do not properly match up. When this happens, the doubled image combining the odd and even lines is jagged and distorted. Line doublers must correct for this misalignment and also for movement between fields in order to create an image that is of high quality. ue to the difficulties inherent in line doubling, line doublers are expensive and are not mainstream products. Additionally, line doublers must be used with data or graphics grade projectors. These types of projectors have the necessary scan rate to be able to paint the additional lines in the image (a line doubler requires twice the scan rate and thus cannot be used with most televisions or projectors). However, a quality line doubler creates a highly superior image compared to standard video.