Bryan Parkoff replied: >"Michael J. Mahon" wrote in message >news:20040626040152.16528.00000476@mb-m22.aol.com... >> Bryan Parkoff wrote: >> >> > Do you see that Apple IIgs' RGB monitor displays one dot per pixel? >If >> >you type in Applesoft BASIC like below. >> > >> >10 HGR >> >20 HCOLOR=2 >> >30 HPLOT 0,0 TO 100,100 >> >RUN >> > >> > It displays a violet line from (0,0) to (100,100). Do you notice >that a >> >pair of pixels do not get close together that it only displays one dot >per >> >pixel? Now, compare to NTSC. Do you notice that it displays three dots >per >> >pixel? It is because NTSC's beam to light three dots per pixel, but it >> >looks like that it is really five dots or six dots per pixel. >> >> I believe that you are confusing the dots created by the CRT's shadow >> mask with pixels. >> >> Try plotting a single point and look at the screen. Then plot two >adjacent >> points (which will appear to be white) and look at the screen. >> >> Apple pixels are, indeed, single pixels, but when sent to a monitor >> using NTSC encoding, the bandwidth is limited and the dots are >> smeared somewhat. If you see multiple discrete dots in a single >> Apple pixel, this is not in the video signal, but in the shadow mask >> just behind the CRT's screen. >> >> If you want to see what is actually going on, you should look at >> the Apple video signal with an oscilloscope. That will make it quite >> clear that an Apple pixel is a single pulse, regardless of "color". >> >> The color of a displayed pixel is an artifact of the phase (timing) >> of the pulse with respect to the color reference burst. The video >> signal is simply a sequence of pulses, one per "on" pixel, each >> of the same amplitude (even the "runt pulse" that occurs when >> a pixel pulse is cut short by a change in "color set" between >> video bytes). It is the location and duration of these pulses >> that produce the apparent color of the display. > > Thank you for the information. I do understand that Apple II's picture >signal always outputs one dot per pixel, but video monitor displays three >dots per pixel that is called shadow mask CRT. It does make sense that it >is how NTSC is designed to use shadow mask CRT unlike Apple IIgs' RGB >monitor. The RGB monitor uses a shadow mask, too, but the bandwidth of the RGB signal is high enough that a pixel is not "stretched" to cover more mask holes. The finer the shadow mask, the more "dots" you will see for a single pixel, even if driven by an RGB signal. These dots have to do with the construction of the CRT and the width of the video pulse, not the number of pixels displayed or their color (though different spots on the CRT will illuminate for different colors). > I am trying to simulate RGB pixel into NTSC's shadow mask CRT. I would >not be able to find any information on the website using google search. My >goal is to write C++ source code by translating RGB pixel into NTSC's shadow >mask CRT. NTSC screen will look real on SVGA monitor. Curious--you are trying to emulate the bandwidth limitations of NTSC on a high-resolution monitor! One approach is to take high-resolution digital photos of an NTSC monitor screen, then present them on a high resolution monitor. > Can you please help me to find the information like source code, graphic >/ video functions including shadow mask CRT formula and YIQ formula for >translating from RGB to NTSC while I am searching right now. I didn't bother to invert the RGB-to-YIQ matrix an earlier respondent supplied, but I did happen to come across an YCrCb-to-RGB matrix. There are various such matrices dependent on exact color models, but this is one typical of TV (with all components from 0..256): R = 1.164*(Y-16) + 1.596*(Cr-128) G = 1.164*(Y-16) - 0.813*(Cr-128)-0.392*(Cb-128) B = 1.164*(Y-16) +2.017*(Cb-128) Note that the Cr and Cb values are excess-128 signed, while the Y values are absolute. Also note that in TV signals, there is a luminance "setup" of 16 units to provide margin for the blanking signals to be "blacker than black". -michael Check out amazing quality sound for 8-bit Apples on my Home page: http://members.aol.com/MJMahon/