Office europeen des brevets (fi) Publication number : 0 566 229 A2 @ EUROPEAN PATENT APPLICATION @ Application number: 93300903.7 @ Int. CI.5: G09G 1/16 (22) Date of filing : 05.02.93 (30) Priority : 05.02.92 US 830409 (72) Inventor : Vogeley, James H. 210 York View Road (43) Date of publication of application : Yorktown, Virginia 23692 (US) 20.10.93 Bulletin 93/42 Inventor: Kosin, Kenneth 4 Marcel la Road @ Designated Contracting States : Hampton, Virginia 23666 (US) AT BE CH DE DK ES FR GB GR IE IT LI LU NL Inventor : Jones, Garth S. PT SE 940 Royal Oak Close Virginia Beach, Virginia 23452 (US) (7i) Applicant : nVIEW CORPORATION Inventor : Trani, Stephen S. 11835 Canon Boulevard 315 24th Street Newport News, Virginia 23606 (US) Virginia Beach, Virginia 23451 (US) (74) Representative : Smith, Martin Stanley Stevens, Hewlett & Perkins 1 St. Augustine's Place Bristol BS1 4UD (GB) (54) Method and apparatus for deinterlacing video inputs. (57) Disclosed is a method and apparatus for con- verting interlaced input video to a sequential output compatible with sequential input display devices. The video input is digitized and de- coded so as to provide separate luminance or chrominance information for each pixel to a line buffer memory. A line derived frequency refer- ence from the input video serves to reference a pixel clock which clocks pixel information into the memory and clocks pixel information out of the memory at twice the pixel clock rate. The decoder also digitizes the luminance/chromi- nance information prior to storage in the mem- ory and, as this information is read out of the memory, it is converted back into analog data by a suitable D-A converter and then is conver- ted into appropriate format to provide red, green and blue video output information for OS operating sequential input devices. 0 CO LU Jouve, 18, rue Saint-Denis, 75001 PARIS 1 EP 0 566 229 A2 2 BACKGROUND OF THE INVENTION able to combine television video inputs with computer generated video inputs to drive such non-interlaced 1. Field of the Invention devices or sequential input devices, which, in Europe, are called progressive scan devices and include ma- The present invention relates to a method and ap- 5 trix devices (such as LCD display panels) which have paratus for converting interlaced raster scan video in- been manufactured for sequential address operation. puts to a non-interlaced sequential output for driving Quite obviously, if every other line is not supplied, the cathode ray tubes, a three gun projector, liquid crystal picture quality will be seriously degraded. displays or any other sequential input display device. Several attempts have been made in the past to 10 directly drive non-interlaced devices with convention- 2. Discussion of Prior Art al video inputs, most often by deleting one of the two fields utilized in making up the frame to be displayed. Conventional television signals are generally This is illustrated in Figures 2A-2C which shows that conveyed in either NTSC, PAL, or SECAM formats. the second field, shown in Figure 2B as T2, contains Each of these formats utilizes a raster scan in which 15 no data and thus only the scanning of the odd num- the electron beam "paints" a picture by causing a bered lines (1 , 3, 5, etc.) comprises the video data dis- number of lines of pixel elements to phosphoresce played. As a result, the diagonal line which is dis- when stimulated by the electron beam in the cathode played as shown in Figure 2C will be relatively weak ray tube. For discussion of various problems in prior or diluted because it is missing the even numbered art devices NTSC black and white television video will 20 lines and pixel information. used with its 30Hzand 60Hz frame and field rates, re- Figures 1 A through Figure 8 in this application il- spectively. lustrate single pixels in a "black and white" represen- During scanning, in order to reduce signal band- tation have been shown. Differences in cross hatch- with required to transmit or store television images, ing represent pixels energized in one or the other of each of the above videos utilizes "interlacing". Inter- 25 the two fields illustrated and, where there are two lacing is a term applied to image scanning in which, lines of cross hatching in single pixel, that indicates during one field or sequence of lines painted by the that the pixel has been illuminated or energized in electron beam, the even numbered lines would be both fields of the frame illustrated. Quite clearly, en- painted and subsequently, in the next field, the odd ergization in a black and white representation could numbered lines would be painted. The fields are gen- 30 be either black or white or any one of a number of erally provided at a 60 Hz field rate (so as to provide shades of gray in between. However, it should also be a 30 Hz frame rate with each frame comprising two understood that although black and white has been fields) and the "persistence" of the individual phos- chosen for simplicity of understanding of applicant's phors is such that, when stimulated to emit light, the invention, the same problems and same advantages human eye can see no difference between the fields 35 appear with respect to color although due to the re- and "perceives" the picture to be flicker free even at quirement of providing red, green and blue output en- the provided 30 Hz frame rate. ergization levels, the pixel represented by a dot of col- Figures 1A-1C illustrate a typical video raster or would actually be three sub-pixels, each represent- scan input and its operation. Figures 1A-1C numbers ing one of the primary colors. the lines being painted as well as the pixel number be- 40 Another attempted solution to the problem of con- ing painted along the vertical and horizontal axes, re- verting interlaced raster scan video to a sequential spectively. In Figure lAwhich is identified as T1 indi- video for driving non-interlaced devices is to utilize a cating the first field, the odd numbered lines are scan- dual port frame buffer memory system. A character- ned and for this particular input image (a diagonal line istic of such a dual port system is that it can enter and from the upper left to the lower right), pixels 1 and 3 45 store data in the system at the same time data is be- are energized in lines 1 and 3 respectively. In the sec- ing read out of the system, hence the name "dual ond frame shown in the second field as shown in Fig- port" memory. However, the storage requirements of ure 1B as T2, the even numbered lines are scanned such a memory are rather substantial. Many output with a result that pixels 2 and 4 are energized in lines devices have a field 640 pixels wide x 480 lines high, 2 and 4. The result due to the persistence of the phos- so which, if color is provided, each pixel is comprised of phors on a television screen is the "averaged" image three subpixels. Both fields T1 and T2 would be read shown in Figure 1C which results in the desired diag- into such a memory so that it contains both the odd onal line image. numbered lines and the even numbered lines at the Computers which provide serial non-interlaced same time. Then, the data is sequentially read out for outputs, are used to drive various display devices 55 line 1, line 2, line 3, line 4, etc. The memory require- such as three gun projectors, liquid crystal display de- ments of the above is quite extensive and expensive. vices as well as cathode ray tubes at picture rates of Video, when displayed by a high resolution dis- 50-80 Hz. Increasingly it has been desirable to be play device, has particular problems in displaying vid- 2 3 EP 0 566 229 A2 4 eo motion. It is known that a 30 Hz frame rate is about reference from the input video serves to reference a at the limit of perceived flicker for the human eye. pixel clock which clocks pixel information into the Where the leading edge of an image in motion across memory and clocks pixel information out of the mem- the screen moves the pixels at the leading edge 5 ory at twice the pixel clock rate. The decoder also change at a 30 Hz rate for those devices which store digitizes the luminance/chrominance information pri- both even and odd interlaced fields in a frame store or to storage in the memory and thus, as this infor- memory. This 30 Hz change or flicker at the leading mation is read out of the memory, it is converted back edge of a moving image can be very annoying to the into analog data by a suitable D-A converter and then viewer espescially in a high resolution output device 10 is converted into appropriate format to provide red, because it occurs at a 30 Hz rate. This phenomenon green and blue video output information for operating has been called "dynamic jaggies" by those in the sequential input devices. field and is a significant problem in displaying video on n high resolution displays. BRIEF DESCRIPTION OF THE DRAWINGS In view of the above, there is a need for an inex- 15 pensive effective manner of converting raster scan in- A more complete understanding of the above in- terlaced video to a non-interlaced format for driving vention will be had by reference to the following draw- video display devices while at the same time reducing ings wherein: perceived flicker and maintaining image resolution.