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TMC22X5YA Datasheet(PDF) 48 Page - Fairchild Semiconductor |
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TMC22X5YA Datasheet(HTML) 48 Page - Fairchild Semiconductor |
48 / 84 page TMC22x5yA PRODUCT SPECIFICATION 48 REV. 1.0.0 2/4/03 The comb filter architecture performs chrominance or lumi- nance comb filtering on PAL or NTSC video signals, by implementing one of sixteen independent chroma and luma comb filter algorithms. The highest level of the adaptive comb filter configuration is determined by the STA[3:0] register bits as shown in Table 3. Table 3. Comb Filter Architecture The COMB signal can be produced in two ways. The first method uses the comb fail detection circuits to select one of several comb filter architectures. These comb filter architec- tures weight the three lines by varying degrees depending upon the degree of picture correlation between the inputs to the comb filter. The simple example in Table 4 shows how this process works, in which upper denotes error compari- sons between the two lines stores and lower denotes error comparisons between the input and the first line store. The 0H, 1H, and 2H terms used in the mathematical description of the comb filter selection refer to the position with respect to the internal line stores. The 0H term is the undelayed input, 1H is the output of line store 1, and 2H is the output of line store 2. In this example a 3 line comb is implemented when in the flat areas of blue or yellow. However, when a difference between the inputs is detected the 3 line comb filter adapts to the 2 line comb filter whose inputs have the smallest differ- ence. This illustrated on line n+4, at which time the comb filter adapts to inputs from 1H (blue) and 2H (blue) and ignores the 0H (yellow) inputs. In cases where there is a difference between all inputs to the comb filter, a 3 line comb filter is selected and the highest set of comb fail signals are sent to the XLUT input logic. This technique would work well if pictures only contained vertical transitions, which is obviously not the case. There- fore the weighting of these comb filter taps, (0H, 1H, and 2H), are rarely just the simple ratios shown in Table 4. It is worth noting that comb filters that use an even number of lines in the comb filter architecture produce chrominance and luminance signals that are vertically offset by one pic- ture line, i.e. in the middle of the even number of lines used in the comb filter input. While comb filters that use an odd number of lines, in the comb filter architecture, the chromi- nance and luminance produced is referenced to the center, i.e. the middle line, of the comb filter. This approach can consequentially cause aliasing in decoding composite video signals containing high frequency diagonal transitions. The FAST register bit, when set LOW, filters the comb filter selection to decrease the sensitivity of the adaption algo- rithm. The second method completely disables the adaption between different comb filters, by setting the ADAPT[1:0] register bits accordingly, see Table 5. STA[3:0] Comb Filter Description 0 YC or Composite, PAL or NTSC, 3 line comb 1 YC or Composite, NTSC, 3 line comb (0H & 1H) 2 YC or Composite, NTSC, 3 line comb (1H & 2H) 3 YC or Composite, NTSC, 2 line comb (0H & 1H) 4 YC or Composite, NTSC, (2 line) field comb 5 YC or Composite, NTSC or PAL, field comb 6 YC or Composite, NTSC, (2 line) frame comb 7 YC or Composite, NTSC, frame comb 8 D1, Y or CBCR, 3 line comb 9 D1, Y or CBCR, 3 line comb (0H & 1H) 10 D1, Y or CBCR, 3 line comb (1H & 2H) 11 D1, Y or CBCR, 3 line comb (0H & 2H) 12 D1, Y or CBCR, (2 line) field comb 13 D1, Y or CBCR, field or 2 line comb (0H & 1H) 14 D1, Y or CBCR, (2 line) frame comb 15 D1, Y or CBCR, Frame Table 4. Simple Example of an Adaptive Comb Filter Architecture Line no. Input col- or Error signals Comb filter selection upper luma upper sat. upper hue lower luma lower sat. lower hue n+6 blue xxxxxx unknown without line n+7 n+5 blue 000000 [0H/4] + [1H/2] + [2H/4] n+4 blue 0 0 0 >0 0 180 [0] + [1H/2] + [2H/2] n+3 yellow >0 0 180 0 0 0 [0H/2] + [1H/2] + [0] n+2 yellow 000000 [0H/4] + [1H/2] + [2H/4] n+1 yellow 0 0 0 >0 >0 >0 [0] + [1H/2] + [2H/2] n black xxxxxx unknown without line n-1 |
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