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MIT 6 111 - Study Guide

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itu.intBroadcasting service (television)video-demystified.comVideo-Demystified.comXAPP285 (1.0) December 17, 2001 www.xilinx.com 11-800-255-7778© 2001 Xilinx, Inc. All rights reserved. All Xilinx trademarks, registered trademarks, patents, and disclaimers are as listed at http://www.xilinx.com/legal.htm. All other trademarks and registered trademarks are the property of their respective owners. All specifications are subject to change without notice.Summary One of the more frequent video conversions needed between various consumer video input devices, video processing, and output devices is interlaced to non-interlaced conversion. This process is sometimes called de-interlacing, scan-line doubling, or progressive scanning. This application note and reference design provides technical details surrounding video de-interlace and how it is implemented in the MicroBlaze™ and Multimedia development board.Introduction Analog video is sampled, converted to digital data, and de-interlaced by the MicroBlaze and Multimedia development board for further processing. The format for the digital video input from the video decoder (Analog Devices ADV7185) on the development board is described by the standard ITU-R BT.656 and explained in application notes: XAPP248 "Digital Video Test Pattern Generator" and XAPP286 "Video Line Field Decode". The component video from the Analog Devices decoder in Y'CrCb interlaced format is presented to the FPGA for further processing.An entire picture, or frame, requires two passes of the electron beam across the face of a display. Each of these events is termed one field. Interlaced video draws the odd lines in a frame, the odd field followed by the even field. Historically, this concept allowed the overall pixel bandwidth to be reduced by a factor of two over frame rate displays requiring all of the lines to be drawn every frame. Although it results in cheaper displays, PC boards, and digital logic designs, the downside of this method is noticeable flicker and other artifacts.For vertical field and frame detail, as well as horizontal line detail, refer to XAPP248 and XAPP286. For an official copy of the ITU-R BT.656 standard, go to the International Telecommunication Union web site and for a small fee obtain a PDF or DOC describing the specification:http://www.itu.int/itudoc/itu-r/rec/bt/656-4.htmlThere are several methods of accomplishing de-interlace, each with a performance or cost trade off. Four common methods examined here are: field scan-line duplication, field scan-line interpolation, and multiple field processing or field merging, and frame scan-line interpolation. The description of the de-interlacing process that follows is centered on the national television standards committee (NTSC), but can be extended to the phase alternating line (PAL) format as well. Design files for frame scan line interpolation (Method 4) are included with implementation results.For NTSC, the MicroBlaze and Multimedia development board builds non-interlaced images assuming the first line of video in the non-interlaced or progressive image comes from the interlaced image line 21 (field 1 or the odd field). The next progressive line comes from the interlaced line 284 (field 2 or the even field), and so on. Figure 1 shows interlaced active video fields combined to form non-interlaced active video images in the development board. Application Note: MicroBlaze and Multimedia Development BoardXAPP285 (1.0) December 17, 2001Video Scan Line De-InterlacingAuthor: Gregg HawkesR2 www.xilinx.com XAPP285 (1.0) December 17, 20011-800-255-7778Video Scan Line De-InterlacingRMethod 1 Simple Field Scan-Line Duplication or 2X Vertical ZoomThe first method is simple field scan-line duplication (sometimes referred to as 2X vertical zoom). The basic algorithm takes a field in the interlaced picture and forms a non-interlaced picture requiring double the lines. To do this, each scan is simply output twice to the output frame buffer. The destination addresses for the two pixels are exactly 1 line different. With this method, vertical resolution is not doubled, even though the number of scan lines is. This method will exhibit artifacts, such as single pixel width lines will flicker or jitter at the field rate. Figure 2 and Figure 3 show how the frames are composed from the separate fields.Figure 1: Non-Interlaced Image from Interlaced Fieldsx285_01_120501NTSC line 283, Field 2NTSC line 21, Field 1NTSC line 284, Field 2NTSC line 22, Field 1NTSC line 261, Field 1NTSC line 260, Field 1NTSC line 523, Field 2NTSC line 522, Field 2NTSC line 285, Field 2NTSC line 23, Field 1NTSC line 286, Field 2NTSC line 24, Field 1NTSC line 263, Field 1NTSC line 262, Field 1NTSC line 525, Field 2NTSC line 524, Field 2SMPTE 170M FIELD 1 and 2242 1/2 linesProgressive Line 1Progressive Line 2Progressive Line 3Progressive Line 4Progressive Line 5Progressive Line 6Progressive Line 7Progressive Line 478Progressive Line 479Progressive Line 480Progressive Line 481Progressive Line 482Progressive Line 483Progressive Line 484485 total active lines 484 total active linesFigure 2: Progressive Image from Duplicating Lines from Field 1x285_02_120501NTSC line 21, Field 1NTSC line 22, Field 1NTSC line 261, Field 1NTSC line 260, Field 1NTSC line 23, Field 1NTSC line 24, Field 1NTSC line 263, Field 1NTSC line 262, Field 1SMPTE 170M FIELD 1242 1/2 linesProgressive Line 1Progressive Line 2Progressive Line 3Progressive Line 4Progressive Line 5Progressive Line 6Progressive Line 7Progressive Line 478Progressive Line 479Progressive Line 480Progressive Line 481Progressive Line 482Progressive Line 483Progressive Line 484 484 total active linesVideo Scan Line De-InterlacingXAPP285 (1.0) December 17, 2001 www.xilinx.com 31-800-255-7778RThe MicroBlaze and multimedia development board has ZBT RAM for frame buffers. With ZBT RAM there is latency for read or write, but any address can be accessed in any order. This feature allows groups of pixels to be composed, out of order, and written into the frame buffer.Each pixel consists of 24 bits (eight-bit video components) or 30 bits (ten-bit components, studio quality) Y’CrCb in 4:4:4 pixel format. This assumes the conversion from 4:2:2 format to 4:4:4 format as described in the application note: XAPP294: "Digital Component Video Conversion - 422 to 444" has happened earlier in the video pipe. The video development board supports studio quality, 10-bit video components, with 12-bit


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MIT 6 111 - Study Guide

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