Groups > comp.sys.apple2.programmer > #2341

Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules"

Newsgroups	comp.sys.apple2.programmer
Date	2016-02-21 09:55 -0800
References	(8 earlier) <df41d156-e664-40d0-9f29-ac57dcc5687f@googlegroups.com> <4fccb972-ff46-46f0-bc87-8ac47595a91e@googlegroups.com> <6f54d44b-ef84-4426-b3ec-4999fd5efec5@googlegroups.com> <e7357125-a0ff-4ac4-b83b-23c9d5c01b23@googlegroups.com> <5e9d07fc-f692-46e6-a455-3c3a358b0ec4@googlegroups.com>
Message-ID	<e2f2149e-a895-4160-8672-4d7d4124788d@googlegroups.com> (permalink)
Subject	Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules"
From	gids.rs@sasktel.net

Show all headers | View raw

On Sunday, February 21, 2016 at 4:29:49 AM UTC-6, denisb...@gmail.com wrote:
> On Sunday, 21 February 2016 20:41:05 UTC+11, wss...@gmail.com  wrote:
> > Am Sonntag, 21. Februar 2016 17:23:42 UTC+9 schrieb denisb...@gmail.com:
> > > This is the 'two-byte' system that I was referring to earlier. Unfortunately I cannot make it work and I believe it is wrong. The description on pp 19-20 of the Apple ][ Reference Manual is brief and quite clear, it explains how everything works without resorting to odd and even bytes.
> > > 
> > > The only thing it doesn't explain is the smudging between non-adjacent pixels, which others have already covered.
> > > 
> > > Personally I would prefer it if everyone used the notation with Most Significant Bit on left (also called the Color Bit) and Least Significant Bit on the right, but I can usually work out what they mean if they use it backwards. I agree it is confusing when the first (least significant, or rightmost) bit of the first byte appears on the left-hand edge of the screen, but that's just the way it is.
> > > 
> > > I think the most important paragraph in the Apple manual is the one which begins - 'Each dot on the screen represents one bit from the picture buffer. Seven of the eight bits in each byte are displayed on the screen, with the remaining bit used to select the colors of the dots in that byte.'
> > > 
> > > In my opinion, any interpretation which disagrees with those two sentences must be wrong. So no need for odd/even bytes, and no using two bytes to represent 7 pixels. Nowhere does it mention 'the two sequential bits that make up a colored pixel' or 'the even/odd byte pairs that make up the 7 colored pixels'.
> > 
> > The way I read this, you aren't wrong. But neither is the person you are responding to.
> > 
> > The reason that even and odd bytes come into play is that there are only 7 bits in each byte that correspond to dots on the screen. But it takes two consecutive dots to make a given color. Since 7 is not evenly divisible by two, one of those two-bit pairs is split between the even and odd bytes.
> > 
> > Suppose the first two bytes on a line are $55, $55. In binary this is 01010101, 01010101. The video scanner puts these two bytes on the HGR screen low bit first, so it will put them out like this:
> > 
> > A A A AB B B B
> > 
> > Where As are dots generated from the first byte and Bs are dots generated from the second byte.
> > 
> > The first A in the line is going to be colored purple because the first two bits are 10.
> > The second A will also be colored purple because the next two bits are also 10.
> > The third A will also be colored purple because the next two bits are also 10.
> > The fourth A will be colored white, as will the first B, because together they make a 11 bit pair.
> > The second B will be colored green, because the two bits after the AB are 01.
> > The third B will also be colored green because the next two bits are 01.
> > The fourth B will also be colored green because the next two bits (the last two in the sequence) are 01.
> > 
> > You see that even though both of the two bytes have the same value ($55), they generate different colors because one is in an even position and the other is in an odd position. You also see that the middle pair of bits contains one bit from each of the bytes, and since they are both ones in this case, together they generate a white dot on the screen.
> > 
> > Now, to get back to the question of using two bytes to generate 7 pixels, the fact of the matter is that on a TV set or regular composite color monitor, the purple or green colors generated by a 10 or 01 pair span both pixels of the pair (that is, both the 0 and the 1 appear to take on the color. In other words, if you do the exercise above you don't see a purple dot, a black dot, a purple dot, a black dot, a purple dot, a black dot, two white dots, a black dot, a green dot, etc.
> > 
> > Instead you see a short purple line, followed by a white dot, followed by a short purple line, with no black space at all. So effectively, it takes two bits to generate one color dot, and the horizontal color resolution of the Apple II HGR screen is 140 pixels. So if you think of a pixel as 2 bits wide, which is true as a practical matter, then it takes two bytes to generate 7 pixels.
> 
> I would be interested in your description of how the two-byte system interprets $0066. Because when you pair up the bits, you get 00-00-00-01-10-01-10 (after removing the two colour bits which are both zero. I simply must be misunderstanding your explanation because you seem to be saying that this pattern will generate alternating green and purple pixels. But I'm pretty sure that it will generate two lots of two white pixels. As the manual states 'two colored dots side by side always appear white, even if they are in different bytes'.


Again you are mis-reading the post.  It does not say alternating pixels, it says alternating bytes.  Which means, the odd byte is the alternate of the even byte to give the same color.

For each even/odd byte pair, to get a solid colored line you will have these alternating values, not including the most significant bit (way easier and shorter to say hi-bit or MSB, I will use MSB in the remainder of the post)

2000: 55 2a  - violet line
2000: 2a 55  - green line
2000: d5 aa  - blue line
2000: aa d5  - orange line


breaking down 55 and 2a - the MSB is on the left.

55 - 0101 0101
2a - 0010 1010

as you can see the bits are alternating, not counting the MSB

d5 - 1101 0101 - do not confuse the double one's here as a pixel, the MSB only allows the second color group to be displayed blue/orange
aa - 1010 1010


And from previous posts, by now you should also be able to assess that bit# 6 of each even byte combines with bit# 1 of the next byte (which is the odd byte) for its pixel color (and in other posts is known as pixel #3).

Thread

Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-15 11:40 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-15 12:33 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-15 12:38 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-15 14:11 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" dempson@actrix.gen.nz (David Empson) - 2016-02-16 14:22 +1300
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-15 18:33 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-15 14:08 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-15 19:39 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-15 19:47 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" David Schmidt <schmidtd@my-deja.com> - 2016-02-15 23:25 -0500
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-16 08:42 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-16 11:28 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-18 14:53 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-18 15:28 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 15:31 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-18 15:42 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 15:52 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 16:09 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 16:42 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-22 11:01 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" dempson@actrix.gen.nz (David Empson) - 2016-02-19 12:47 +1300
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 15:49 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 16:02 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-16 11:34 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-16 12:00 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-16 13:47 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-16 13:41 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-16 19:02 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-17 18:09 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" marc.depeo@brbent.com - 2016-02-18 00:43 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-18 01:48 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" AppleIIGSMarc <appleiigsmarc@gmail.com> - 2016-02-18 08:50 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" AppleIIGSMarc <appleiigsmarc@gmail.com> - 2016-02-18 10:45 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-18 20:24 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-18 20:32 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" AppleIIGSMarc <appleiigsmarc@gmail.com> - 2016-02-18 21:05 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-18 15:08 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-18 15:31 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-18 13:18 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-18 18:15 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-03-01 11:58 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-16 14:05 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-16 19:12 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" "Michael J. Mahon" <mjmahon@aol.com> - 2016-02-17 15:22 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-17 16:14 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-19 14:34 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-19 16:17 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-19 19:19 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-19 22:25 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-19 23:12 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-19 23:27 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-19 23:31 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-20 04:02 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-20 11:40 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-20 11:48 -0800
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-20 08:10 -0800
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-20 16:25 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-20 16:37 -0800
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-20 18:29 -0800
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-20 20:00 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-02-20 20:53 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-20 23:11 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-21 00:23 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-21 01:41 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-21 01:43 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-21 02:29 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-21 02:40 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" wssimms@gmail.com - 2016-02-21 08:03 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-21 09:55 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-21 10:28 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-02-21 14:42 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael J. Mahon <mjmahon@aol.com> - 2016-02-22 14:13 -0600
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-02-21 20:49 -0800
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" anthonypaulo@gmail.com - 2017-06-22 17:19 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2017-06-22 18:05 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" awanderin <awanderin@gmail.com> - 2017-06-22 23:00 -0600
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael J. Mahon <mjmahon@aol.com> - 2017-06-23 12:59 -0500
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" David Schmenk <dschmenk@gmail.com> - 2017-06-23 13:12 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2017-06-25 07:30 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" anthonypaulo@gmail.com - 2017-06-25 08:30 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael J. Mahon <mjmahon@aol.com> - 2017-06-25 13:55 -0500
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Charlie <charlieDOTd@verEYEzon.net> - 2017-06-23 11:26 -0400
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2017-06-25 07:45 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" anthonypaulo@gmail.com - 2017-06-25 08:33 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" anthonypaulo@gmail.com - 2017-06-25 08:38 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" David Schmenk <dschmenk@gmail.com> - 2017-06-25 12:07 -0700
                Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" anthonypaulo@gmail.com - 2017-06-25 16:29 -0700
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael J. Mahon <mjmahon@aol.com> - 2016-02-20 00:27 -0600
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" denisbytezone@gmail.com - 2016-02-19 23:14 -0800
  Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-03-01 11:48 -0800
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael J. Mahon <mjmahon@aol.com> - 2016-03-01 16:24 -0600
    Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Mark Lemmert <mark.lemmert@gmail.com> - 2016-03-02 10:05 -0800
      Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Finger <mike.finger@gmail.com> - 2016-04-06 13:21 -0700
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2016-04-06 13:32 -0700
        Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2016-04-06 15:15 -0700
          Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2017-06-25 06:17 -0700
            Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" gids.rs@sasktel.net - 2017-06-25 21:33 -0700
              Re: Assembly Hi-Res Graphics, question about color patterns that seem to violate the "rules" Michael Pohoreski <michael.pohoreski@gmail.com> - 2017-06-26 11:12 -0700

csiph-web