[Coco] Compressed pictures

[Arthur Flexser]

I'm not sure about the Delphi and Compuserve archives.  I recall somebody on
this list archived the Delphi CoCo SIG MESSAGE base on a CD, but I'm not sure
about whether anybody has archives of the data libraries.  Come to think of it,
what does SIG stand for, again?  <something or other> Interest Group, I think.  
A term I haven't heard in a long time.  Special Interest Group?  Subject
Interest Group?  Was this term used in places other than Delphi and Compuserve?

MAXCMP.BAS was descended from the earlier PIXCMP.BAS, and added the capability
of compressing double-screen CoCo Max pictures as well as PMODE 3 single
screens, allowing scrolling of the double-screen ones by the arrow keys.  The
point of having the graphics converted to printable ascii characters was to
allow the transmission of graphics as text files, in the days before CoCo
terminal programs were routinely capable of transmitting binary files, and when
BBSes often restricted uploads to text files.  This "asciifying" step increased
the size of the compressed graphics by a factor of 8/6 (1.33), since only the
lower 6 bits of each ascii character could be used for representing the
graphics.  The Compuserve and Delphi program data libraries had a large number
of graphics files encoded using PIXCMP and MAXCMP.

Art

On Sat, 28 Apr 2007 coco at yourdvd.net wrote:

> Hello Arthur: I have wondered recently if there existed archives of the
> Delphi and CompuServe CoCo SIG's from back in the day. Are they online
> somewhere (perhaps at delphi or compuserve themselves? I suppose I
> could do some searching)... Thanks - Robert
> P.S. I remember the program of which you speak, the one you wrote. I
> think it was the one I used to transmit graphics screens as ascii
> rather than binary many moons ago.. r
> 
> > -------- Original Message --------
> > Subject: Re: [Coco] Compressed pictures
> > From: Arthur Flexser <flexser at fiu.edu>
> > Date: Sat, April 28, 2007 4:05 pm
> > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > 
> > It is unclear why you would find LOADMing a 6K screen "too much";  it
> > shouldn't
> > take much time to load, and the fact that it is 3 times longer than
> > the main
> > program seems to me not particularly relevant.  If you want to
> > compress the
> > picture, a decent algorithm is to use byte, rather than bit,
> > repetitions and
> > think of the screen as a series of 8-bit wide byte columns.  The same
> > byte
> > repeats very frequently in vertically adjacent positions in a typical
> > graphics
> > screen.  A program I co-wrote years ago, MAXCMP.BAS, uses this and may
> > be online
> > somewhere in a CoCo archive. (That one took the additional step of
> > converting
> > the resulting screen to printable ASCII bytes and embedding the resulting
> > encoding into a generated BASIC program that when run displayed the
> > picture.  
> > It was listed and written up in some issue of Rainbow, in one of Marty
> > Goodman's
> > columns.  It should also be in the Delphi archives, along with a detailed
> > description of its compression algorithm.)
> > 
> > Art
> > 
> > On Sat, 28 Apr 2007, Diego wrote:
> > 
> > > While writing some of my BASIC programs, I thought about adding a intro
> > > screen. The options were add the drawing commands to the program (slow,
> > > limited) or load a graphic screen. But even a PMODE 3 screen is 6Kb,
> > a bit
> > > to much for a 2 Kb program So I came up with a very simple compression
> > > rutine. 2 bit for color, 6 bits for how many pixels of that color. Some
> > > sample simple screens came down to just under 1 Kb (I know that some
> > complex
> > > screens can become a lot larger than the original) My question: Is
> > there
> > > some format/way to get a screen picture+loader in less than 2 Kb thatls
> > > already out there somewhere?
> > > 
> > > Diego
> > > 
> > > 
> > > -- Coco mailing list Coco at maltedmedia.com
> > > http://five.pairlist.net/mailman/listinfo/coco
> > > 
> > 
> > 
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