george@mnetor.UUCP (George Hart) (10/27/88)
In article <148@internal.Apple.COM> casseres@Apple.COM (David Casseres) writes: >In article <74013@sun.uucp> landman@sun.UUCP (Howard A. Landman) writes: >>Here's a hard lower bound. Studies have shown that 2-bit grayscale >>gives you better "perceived" screen resolution than spending the same >>bits on extra 1-bit resolution. Since doing that would give you >>SQRT(2) more pixels in each direction, we know that the "effective" >>resolution of the 96-DPI NeXT screen must be AT LEAST 96 * 1.41 = 135 DPI, >>almost twice that of a Macintosh or Alto. > >We only know this if we know that the NeXT actually uses the 2-bit gray- >scale display to do grayscale anti-aliasing. I have the impression that >it does not; does anyone actually know? "Know"? No but I can spread a reasonable rumor as well as the next person :-). A description of the NeXT (recently posted to alt.next, sorry don't have a reference handy) described the 1 of the four bits as an "alpha channel" used to implement transparency under some circumstances (such as when icons overlap each other). Presumably each pixel in an image can have four values: "black", "white", "transparent", and something else. The transparent value leaves the underlying frame buffer pixel untouched when the image is written to the frame buffer. A similar concept was described 1 or 2 years ago in an article in either IEEE Computer or IEEE CG&A 1 or 2 years ago. Use of 1 bit for transparency would still allow an extra gray level for antialiasing if desired. -- Regards.....George Hart, Computer X Canada Ltd. UUCP: {utzoo,uunet}!mnetor!george BELL: (416)475-8980
mday@cgl.ucsf.edu (Mark Day) (10/28/88)
In article <4763@mnetor.UUCP> george@mnetor.UUCP (George Hart) writes: >In article <148@internal.Apple.COM> casseres@Apple.COM (David Casseres) writes: >>We only know this if we know that the NeXT actually uses the 2-bit gray- >>scale display to do grayscale anti-aliasing. I have the impression that >>it does not; does anyone actually know? > >"Know"? No but I can spread a reasonable rumor as well as the next person :-). > At the NeXT day developer's conference, I was among a group of people who were all trying to get specifics about the Display PostScript implementation from Leo Hourvitz, who had just given a talk on the NeXT windowing system. He said that there is no anti-aliasing in their implementation, and that it would be a very difficult problem to do this with PostScript. He also implied that you wouldn't get much improvement with only a 2 bit gray scale. ---------- Mark Day UUCP: ..ucbvax!ucsfcgl!mday ARPA: mday@cgl.ucsf.edu BITNET: mday@ucsfcgl.BITNET