svermeulen%Janus.MRC.AdhocNet.CA@UNCAEDU.BITNET (Steve Vermeulen) (08/06/88)
Regarding Hedley Monitors:
+From: wayneck@tekig5.PEN.TEK.COM (Wayne Knapp)
+In article <62722@sun.uucp>, cmcmanis%pepper@Sun.COM (Chuck McManis) writes:
+> because the A2024 is actually a "greyscale" monitor rather than a pure
+> "black & white" monitor. You can display > 32 shades of grey with it so
+> 2 bitplanes makes sense. One way to use two bitplanes is to set the
+Is this really true? Sounds great. So can I have a 640x400 display with
+16 levels of gray? Sounds pretty sharp if so.
+ Wayne Knapp
Before this gets even further out of hand: Chuck where did you read
that the Hedley can display > 32 shades of grey? All the material
I have on the Hedley states that it can display only up to 8 shades of
grey when displaying "normal" Amiga screens, and that it can display
up to 4 shades of grey in the very high resolution screen mode.
Do you mean that you can think of ways of dithering to simulate 32 grey
levels or have you received information from Commodore that says you can
display 32 grey levels directly??
Commodore what is the final word on this issue?? I have a manual to
finish...
Stephen Vermeulen
Author: Express Paint
Chairman: AMUC.hedley@cbmvax.UUCP (Hedley Davis) (08/11/88)
In article <880806105940.002@Janus.MRC.AdhocNet.CA> svermeulen%Janus.MRC.AdhocNet.CA@UNCAEDU.BITNET (Steve Vermeulen) writes: >Regarding Hedley Monitors: > >Do you mean that you can think of ways of dithering to simulate 32 grey >levels or have you received information from Commodore that says you can >display 32 grey levels directly?? > > The answer is that you can display four solid looking colors in 1008x800 mode. When the monitor is acting like a deinterlacer for normal amiga displays, you can get eight colors, of which four are dithered. The rest of this note is the gory details of marginal interest. Hedley The monitor can display four grey levels at 1008x800. This is because the monitor only has two bitplanes. The brightness ratios of the four grey levels are moderately adjustable by the user via the contrast control, however the 'best' setting, with contrast all the way up, results in ratios of 0 : 0.25 : 0.5 : 1.0. Note that this is non-linear. In the case of a 200 line display, or a deinterlaced 400 line display, you get the same four solid colors, and an additional four levels of brightness created by dithering two of the four solid colors together on adjacent scan lines. The dithered colors come about because the monitor always scans 800 lines, so each pair of displayed lines comes from a single output line from the Amiga. 400 lines in, 800 lines out ; one line in, two lines out. Each of the four hundred input lines creates two monitor lines, each of which can be any one of four intensities. The monitor uses the R,G,B and I DIGITAL outputs from the amiga. R and B are always mapped to the even lines as most and least significant bits. G and I are always mapped to the odd lines as most and least significant bits. This means each displayed line or pixel can be mapped to one of sixteen values the monitor hardware can see. Unfortunately, the user cannot really distinguish between things like "display full white on only the 400 odd lines" and "display full white on only the 400 even lines". So lets build a table, and see what falls out: RBGI Brightness Brightness Average Even Lines Odd Lines both lines 0000 0 0 0 solid 0001 0 1/4 1/8 dithered 0010 0 1/2 2/8 dithered 0011 0 1 4/8 dithered 0100 1/4 0 1/8 dithered 0101 1/4 1/4 2/8 solid 0110 1/4 1/2 3/8 dithered 0111 1/4 1 5/8 dithered 1000 1/2 0 2/8 dithered 1001 1/2 1/4 3/8 dithered 1010 1/2 1/2 4/8 solid 1011 1/2 1 6/8 dithered 1100 1 0 4/8 dithered 1101 1 1/4 5/8 dithered 1110 1 1/2 6/8 dithered 1111 1 1 8/8 solid Looking at the average column, you can see four solid colors at 0/8, 2/8, 4/8, and 8/8 brightnesses. This is the same as the aforementioned 0 : 0.25 : 0.5 : 1.0 ratios. In addition, you can also create dithered colors at 1,2,3,4,5 & 6 eighths. Note that there is NO 7/8 value in the table. So we concluded that you can get 8 discernable brightnesses in deinterlacer mode. 0-6 eighths, and full white. Of course, two of the solid colors have dithered equivelents which 'look' different than the solid versions. Further, there are several ways to create some of the dithered only levels. These also look marginally different. However, there still remains only 8 distinct brightnesses. I hope this clears things up a tad. Hedley