bartonr@psu-cs.cs.pdx.edu (Robert Barton) (05/19/89)
In article <15500001@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >Broadcast television does not suffer from flicker because the change from >one line (scanned in one cycle) to the next (scanned in the other cycle) >is very little. It just depends on what you're watching. If you have cable, check out CNN Headline News when they show one of their weather maps with the narrow horizontal state lines and you can see flicker in the Midwest. >High Definition Television, unfortunately, is continuing with the interlace >system at about the same frame rate. The proposals I have seen for HDTV also call for 1050 scan lines instead of the current 525 lines. (* -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- *) (* -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- *)
wn0e+@andrew.cmu.edu (William Nichols) (05/20/89)
In article <15500001@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >Broadcast television does not suffer from flicker because the change from >one line (scanned in one cycle) to the next (scanned in the other cycle) >is very little. Just look at special graphics on a tv screen, like those facsimilies of credit cards on a commercial, or the team logos they show on sporting event broadcasts. Look at the graphics on The Computer Chronicals. Anything with distinct horizontal lines of differing contrast. They all flicker like crazy. Untill I got my Amiga, I never really understood why that flicker was there, now I know. On the other hand, many ham displays on the amiga look just like a TV screen, i.e. do not seem to flicker at all. Bill N.
papa@pollux.usc.edu (Marco Papa) (05/21/89)
>In article <15500001@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >>Broadcast television does not suffer from flicker because the change from >>one line (scanned in one cycle) to the next (scanned in the other cycle) >>is very little. You must be joking! Get your facts, dude. Broadcast television suffers the SAME flicker problems that the Amiga shows with images that have 1 scanline tall horizontal lines. This is simply due to the NTSC standard. The flicker on TV is very noticeable during the sports and weather reports. Images that have a lot of color variations don't flicker (on either a broadcast TV or the Amiga) because the eye "averages" the colors. -- Marco Papa 'Doc' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= uucp:...!pollux!papa BIX:papa ARPAnet:pollux!papa@oberon.usc.edu "There's Alpha, Beta, Gamma and Diga!" -- Leo Schwab [quoting Rick Unland] -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
elg@killer.DALLAS.TX.US (Eric Green) (05/22/89)
in article <17324@usc.edu>, papa@pollux.usc.edu (Marco Papa) says: >>In article <15500001@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >>>Broadcast television does not suffer from flicker because the change from >>>one line (scanned in one cycle) to the next (scanned in the other cycle) >>>is very little. > > You must be joking! Get your facts, dude. Broadcast television suffers the > SAME flicker problems that the Amiga shows with images that have 1 > scanline tall horizontal lines. This is simply due to the NTSC > standard. The flicker You're both right. Marco, it's the low contrast of most broadcast pictures that allow the eye to "average" the colors -- i.e., what the guy above said. On the other hand -- I am sick and tired of seeing the output of $10,000 studio character generators crawling across the bottom of my screen. Anti-aliasing? They never heard the word! Nice fonts? Uh uh, no way, Early Timex-Sinclair is the only font they do. > that have a lot of color variations don't flicker (on either a broadcast > TV or the Amiga) because the eye "averages" the colors. The keyword is "Contrast", Marco. The number of colors doesn't enter into it. -- | // Eric Lee Green P.O. Box 92191, Lafayette, LA 70509 | | // ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg (318)989-9849 | | // Join the Church of HAL, and worship at the altar of all computers | |\X/ with three-letter names (e.g. IBM and DEC). White lab coats optional.|
tomb@hplsla.HP.COM (Tom Bruhns) (05/22/89)
> papa@pollux.usc.edu (Marco Papa) writes: >>In article <15500001@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu writes: >>>Broadcast television does not suffer from flicker because the change from >>>one line (scanned in one cycle) to the next (scanned in the other cycle) >>>is very little. > >You must be joking! Get your facts, dude. Broadcast television suffers the >SAME flicker problems that the Amiga shows with images that have 1 scanline >tall horizontal lines. This is simply due to the NTSC standard. The flicker >on TV is very noticeable during the sports and weather reports. Images >that have a lot of color variations don't flicker (on either a broadcast >TV or the Amiga) because the eye "averages" the colors. Well, "dude", the last statement may indicate you need a bit of brushing up on facts yourself. If I build an image with "a lot of color variations" by making the first field of a frame entirely different in intensity (as well as hue and saturation) from the second field, I can about guarantee you will be able to see flicker in it on most standard NTSC tv's. The least flicker is on images that are (1) very similar from one field to the next (e.g., an image with no distinct lines but only gradual spatial changes -- like most program images that are broadcast, except as noted by previous posters. And it probably helps that the images are usually in motion.), and (2) dark. Furthermore, because NTSC also interlaces the color subcarrier with the horizontal (and therefore with the vertical) rates, pictures with highly saturated colors, when displayed on a monitor that doesn't try to play games with what it "thinks" should be luminance and what should be chrominance, will show a lot of _color_ flicker. This is particularly noticable on sharp vertical edges between saturated colors. There are perhaps some practical lessons in this for those who would like to keep down flicker on interlaced (computer) screens: -- Since an RGB monitor doesn't use NTSC color encoding, you don't have to worry about the last problem. Your eye may still perceive flicker, though, if one field has significantly more of one of your colors than the other(s). So chose a set of colors for the screen that are not too different in intensity. There's an obvious tradeoff here with legibility of (text) information. -- Keep the intensity low. This is easier to use if your room lighting is also fairly dim. If you can't control the room lighting, you can achieve the same effect with dark glasses, leaving the screen itself fairly bright. -- Use text fonts that put the same number of "on" pixels on each field (that is, on alternate lines). A test of this is to display a few lines of equal signs and/or minuses. The minuses should be two lines high, and the equal signs should have two rows blank between the turned-on rows (or for larger fonts, something equivalent). -- If all else fails, de-interlace the screen (e.g., FlickerFixer). Hope this is useful. > >-- Marco Papa 'Doc' Tom Bruhns tomb%hplsla@hplabs.hp.com
papa@pollux.usc.edu (Marco Papa) (05/22/89)
In article <8169@killer.DALLAS.TX.US> elg@killer.DALLAS.TX.US (Eric Green) writes: >in article <17324@usc.edu>, papa@pollux.usc.edu (Marco Papa) says: >> that have a lot of color variations don't flicker (on either a broadcast >> TV or the Amiga) because the eye "averages" the colors. > >The keyword is "Contrast", Marco. The number of colors doesn't enter >into it. Thanks for being more precise. I stand corrected. -- Marco Papa 'Doc' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= uucp:...!pollux!papa BIX:papa ARPAnet:pollux!papa@oberon.usc.edu "There's Alpha, Beta, Gamma and Diga!" -- Leo Schwab [quoting Rick Unland] -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
papa@pollux.usc.edu (Marco Papa) (05/24/89)
I just got a call from Rick Unland of CBM (most of Byte-by-Byte ray traced images are his, though as usual never credited :-(, who told me that flicker depends BOTH on contrast of luminance AND contrast of crominance (which depends on color variations). So I should'nt have been so quick to back off from my statement. -- Marco Papa 'Doc' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= uucp:...!pollux!papa BIX:papa ARPAnet:pollux!papa@oberon.usc.edu "There's Alpha, Beta, Gamma and Diga!" -- Leo Schwab [quoting Rick Unland] -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=