PD Modes The PD modes were developed jointly by Don Rotier and Paul Turner. Although they're a little complicated, they represent a fair trade-off between color accuracy and transmission time. VIS CODES PD50 93d (decimal) PD90 99d PD120 95d PD160 98d PD180 96d PD240 97d PD290 94d COLOR MODE Y, R-Y, B-Y (See Appendix B) SCAN SEQUENCE Y, R-Y, B-Y NORMAL DISPLAY RESOLUTION PD50 320x256 (all include 16-line header) PD90 320x256 PD120 640x496 PD160 512x400 PD180 640x496 PD240 640x496 PD290 800x616 TRANSMISSION TIMES PD50 49.7 seconds PD90 90.0 seconds PD120 126.1 seconds PD160 160.9 seconds PD180 187.1 seconds PD240 248.0 seconds PD290 288.7 seconds COLOR SCAN TIMES (Y, R-Y, B-Y) PD50 91.520ms PD90 170.240ms PD120 121.600ms PD160 195.584ms PD180 183.040ms PD240 244.480ms PD290 228.800ms TIMING SEQUENCE Note: two complete lines are shown. (1) Sync pulse 20.000 1200hz (2) Porch 2.080ms 1500hz (3) Y scan (from odd line) (4) R-Y scan averaged for two lines (5) B-Y averaged for two lines (6) Y scan (from even line) Repeat until correct number of lines are transmitted for sub-mode
Appendix B Y, R-Y, B-Y Color Encoding (Y, R-Y, B-Y) encoding is used in Robot and PD modes, as well as the seldomused Wrasse SC2-120 mode. This method of encoding is also referred to as (Y/C), (Y'U'V'), (Y'CBCR), and other names. Although all these refer to the same overall method of encoding, the exact scalings used vary somewhat by implementation and developer. The encoding used in ChromaPIX and W95SSTV is compliant with ITU BT. Rec. 601. (the 1953 NTSC standard) Because there has been no clearly-defined standard, the scalings described below may vary slightly from those used by other developers. To convert non-linear RGB to [Y, R-Y, B-Y] (scaled 0-255) : Y = 16.0 + (.003906 * ((65.738 * R) + (129.057 * G) + (25.064 * B))) RY = 128.0 + (.003906 * ((112.439 * R) + (-94.154 * G) + (-18.285 * B))) BY = 128.0 + (.003906 * ((-37.945 * R) + (-74.494 * G) + (112.439 * B))) Again, as with RGB encoding, these values can be converted to frequency, for SSTV transmission : Frequency = 1500 + (v * 3.1372549) (where `v' is the Y, R-Y, or B-Y value) Conversely, Y, R-Y, B-Y values scaled 0-255 may be converted back to nonlinear RGB: R = 0.003906 * ((298.082 * (Y 16.0)) + (408.583 * (RY 128.0))) G = 0.003906 * ((298.082 * (Y 16.0)) + (-100.291 * (BY 128.0)) + (-208.12 * (RY 128.0))) B = 0.003906 * ((298.082 * (Y 16.0)) + (516.411 * (BY 128.0))) From: http://www.barberdsp.com/files/Dayton%20Paper.pdf 73 de Roland PY4ZBZ --- In digitalradio@yahoogroups.com, "Simon Brown" <[EMAIL PROTECTED]> wrote: > > Does anyone have a full description of the SSTV PD modes developed by Don Rotier (SK I belive) and Paul Turner? > > Simon Brown, HB9DRV >
