Teletext separated mosaic graphics
wjgo_10009 at btinternet.com
Thu Oct 8 07:40:12 CDT 2020
Doug Ewell wrote:
> Of course, I can create a program or a protocol that takes ordinary
> graphic characters such as < and >, and handles them in some special
> way, but then I am creating a new layer on top of plain text.
So could the twenty-seven control characters in the 1976 teletext
specification be encoded as ordinary displayable characters in plane 14
such that they may, but need not, be used as control characters in such
a program or protocol please?
Other codes used in later teletext formats and videotext formats could
also be encoded if so desired.
By the way, I once had a page on viewdata. I saw an article on viewdata
by Mr Fedida in an issue of the magazine Wireless World and I wrote to
him enclosing a design for a page and he kindly arranged for it to be
keyed in on page 786.
I saw it on a viewdata television in September 1977 and I wonder if it
survives in an archive somewhere. I suppose that it is now part of the
historic graphic art from that era.
I produced my design on a sheet of paper from one of those
quadrille-ruled notebooks intended for arithmetic.
I used black ink for the text, one character per square, and red ink for
the control codes, providing a key below the page diagram.
G for Alphanumerics Green, g for Graphics Green, and so on, H for Hold
In fact, this design, which I called Colour Check, used only the seven
graphic colour codes and the Hold Graphics code, and the graphic
character corresponding to lowercase e.
There was a large red filled rectangle at the left, a large green filled
rectangle at the right, and a large blue filled rectangle centred and
lower down the page. The top line of the green filled rectangle was not
on the same line as the top line of the red filled rectangle: I am not
sure whether it was higher or lower. The three filled rectangles
overlapped and where the overlaps occurred the contiguous graphic
characters were in yellow, white, magenta, cyan as appropriate.
A line typically started with a graphic colour code, green possibly,
red, or blue according to which line, followed by a space and then a
Hold graphics code. So where the control codes to change colour within
the image occurred there was not a space displayed as the Hold Graphics
facility repaced the space with a copy of the previous graphic
The background was black and the fact that I used the graphic equivalent
of a letter e produced the effect that the coloured areas were not solid
filled but had a teletext-format look.
The graphic was centred, there was black to the left, to the right,
above and below.
Some early teletext pages have been recovered from super-VHS tapes that
had recorded television programs.
I am wondering if the early ITV Oracle graphic of the Blue Lady has been
Thursday 8 October 2020
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