Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!portal!cup.portal.com!Radagast From: Radagast@cup.portal.com (sullivan - segall) Newsgroups: comp.sys.amiga Subject: Re: DCTV from digital creations Message-ID: <33866@cup.portal.com> Date: 13 Sep 90 23:59:06 GMT References: <4290@crash.cts.com> <1990Sep10.003304.4678@bushido.uucp> <403@cbmger.UUCP> Distribution: na Organization: The Portal System (TM) Lines: 66 >>> >>>Isn't DCTV the box which gets 256 screen colors by intercepting a 640x400 >>>16 color screen and combining each pair a pixels (4 bits each) into one >>>8-bit pixel? I know there is a box like this. In this case, all well and >>>good, you get 256 out of 16million (I think) colors, but only in 320x400 >>>(or variations... not 640 mode at any rate). This could be a consideration. > >>Ah, is that really true? Just recently I wondered that such a device >>would be even simpler when built into the Amiga replacing the Video >>Hybrid chip. But I found for myself that this wouldn't be such a big >>advantage, because you don't get 256 colors! It's more limited in choice >>of possible color combinations than the ExtraHalfBright mode. I tried >>to imagine an algorithm to make up a palette for a certain set of >>needed colors for a certain image. But I found no solution. > >Nono, I don't think you understand what I was saying. Lemme try a li'l >numerical example... > >On the Amiga's Screen: >pixel 0: F pixel 1: 5 > > 1111 0101 <- binary representation of pixels 0 and 1 in memory The name of the box that does this is the HAM-E device by Black Belt systems. Although 256 colors are theoretically possible, Black Belt limited the number to 240 colors, and gives you 16 palettes (reselectable on the fly) instead. In its other mode, the HAM-E device uses a base palette of 64 24bit colors, and then updates the 7 bits of either red, green, or blue, in a HAM like fashion for each pixel. DCTV is similar in some ways, but isn't limited to working with 4 hi-res bitplanes. Instead it takes advantage of certain redundancies in the NTSC signal definition and makes those combinations impossible to describe thereby making their data somewhat more compact. Thus the DCTV box is capable of somewhat greater output control, as long as the monitor is an NTSC monitor. Instead of changing RGB values like the HAM-E, the DCTV works with Hue, Saturation and Intensity. Since saturation and Hue are co-dependent, (changing one will also change the other over the next pixel or so which is why you get color fringes in NTSC signals when changing between certain colors) they are only modified half as often as the Intensity signal. In general you have control over Intensity on every pixel produced, but only have control over Hue and Saturation on alternate pixels. As a result, DCTV produces quite useful output with 3 bitplanes of high-res input. All of the above was gleaned from open discussions on BIX and from Digital Creations' presentation at the First Amiga Users Group in Palo Alto, California. Any misunderstandings or misrepresentations are purely my own... ...I do not speak for Digital Creations, nor are they accountable for anything I might imagine them to have said. -Sullivan_-_Segall (a.k.a. Radagast) _______________________________________________________________ /V\ "I regret to say that we of the FBI are powerless to act in ' cases of oral-genital intimacy, unless it has in some way obstructed interstate commerce." -- J. Edgar Hoover _______________________________________________________________ Mail to: ...sun!portal!cup.portal.com!radagast or radagast@cup.portal.com Bix: radagast