Note: Descriptions are shown in the official language in which they were submitted.
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The inVention xelates t~ a control a~rangement fo~ the
representation o~ a visual displa~ on ~ display unit screen by
means of which a display can be represented in different colours~
and by means of whi~h not only characters, but also multi-coloured
graphic patterns ~nd/or multi-colour television images can be
represented.
In recent telecnm~lln;c~tions services such as screen text
~Interactive-Videotexj and Video-text (Broadcast ~i~eotex~ it is
possible to represent both characters and graphic patterns in
addition to normal television pictures, using a television display
device. In this context the term "characters" is to be understood
as embracing all alphanumerical characters, special symbols and
linear graphic sym~ols, whereas graphic patterns are to be
understood as relatively coarse graphic representations.
In the representation of characters and graphic patterns,
the screen ~ontent, which ls referred to as a page, is divided
into a number of arrays, for ~mpl e into 960 character arrays
arranged in 24 rows each comprising 40 character arrays. In the
case of the representation of alphAnllmerical characters, one
chaxacter is represented in each character array. In this case
the character array consis~s of 8xlO or 8x12 image points by means
o~ which the individual characters are represented. The same
arra~gement can be used to represent fine graphic symbols, which
can extend over one array or over several character arrays. In
the case of the representation of graphic patterns, each array is
split into 2x3 graphic elements and the graphic patterns can be
constructed from the possible combinations of light and dark
graphic elements.
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The representation of the characters and graphic patterns can take place
in the conventional basic colours used in television - red, green and blue, and
their complementary colours which are yellow, cyan and magenta, and also in
white and black. These colours can also be selected as background colours for
a displayed representation.
When characters are represented in relatively dark colours9 such as for
example red or blue on a dark background, it has been established that on ac~
count of the relatively low light intensity and a simultaneously low spectral
sensitivity of the eye, the characters are difficult to read and recognise in
L0 the case o~ red and blue. ~lowever, coarse graphic patterns represented in red
or blue are easy to recognise.
From the German OS ~7 40 329 (Eikenberg, et al~ laid open March 18,
1978) and the European OS 0 00~ 197 (~art, et al, published Sept. 19, 1979) it
is already known to change the brightness of the colours iE videotex pages are
to be represented instead of television pictures on the screen of a television
device. The adjustment of the brightness of the colours in the representation
o~ the vldeotex pages relative to the brightness of the colours in the represent-
atlon of a television picture is carried out by one single operation and appliesboth to the representation of the characters and oE the graphic patterns. ~low-
ever this method of setting the brightness oE the co:Lours lnvolves tlle danger
that, :Ln the case o~ the representation of graphic patterns, the relatively
`llUht colours such as white, yellow and cyan will be brightened too much re-
lntlve tn the relat:Lvely dark colours such as red and blue, or, in the case of
the representation of characters, the relatively dark colours such as red and
blue will be brightened too little.
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This applies ln particular when both characters and graphic
patterns are represented on one videotex page and relatively dark
characters are represented in the vicinity of large, light areas.
Therefore one object of the present invention is to
provide an arrangement which results in a particularly good
legibility of characters of different colours on a display unit
screen.
The invention consists in a control arrangement for the
representation of a display on a display unit screen, using
dif~erent colours and providing for characters, multi-colour graph-
ic patterns and/or multi-colour television pictures, in which a
control unit is provided to automatically brighten the represent-
ation of characters in relatively dark colours relative to the
comparatively light colours which can be represented and in which
~or representation of characters or symbols in the comparatively
dark colours the control unit supplies the display unit with
control signals by means of which these colours are brightened.
The proposed arrangement has the advantage that it
necessitates only a low outlay in circuitry and can be readily
incorporated into existing display units. I'he observer is present-
~d with an a~reeable image on the screen. In comparision to an
:inc~ease in the overall brightness, the arrangement has the
~dvanta~e that ~lickering o~ the relatively light colours is
avoided and that the colours do not change in the representation
of graphic patterns or television pictures. Furthermore, in the
case of the representation of characters, the colour tone is
maintained as the colours are merely brightened. Mi~ed colours
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are not changed and therefore the colour contrast is likewise
retained.
The arrangement involves a particularly low circuitry
outlay if, in the case of the representation of characters in
the relatively dark colours, the control unit supplies the display
unit with control signals by which these colours are brightened.
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In particular it is ad~ntageous for the contxol signals to increase
the brightness of xepresented charactex~ by the addition of
~orresponding components of the basic colours.
Another possibility of relative b~ightening of the
comparatively dark colours consi~ts in that, in the repxesentation
of characters in the relatively dark colours, the control unit
increases the overall brightness of the representation on the
screen and produces si~nal5 ~7hich reduce the brightn~ess of the
represented relatively light colours.
If a decoder unit is provided which supplies the display
unit with colour signals assigned to the characters which are
to be represented, and which contains an image store which stores
data words assigned to the characters and the associated colours,
an advantageous embodiment of the arrangement is a~hieved in that
the control unit contains a converter which converts first code
words asslgned to the relatively daxk colours into second code
woxds which are assigned to the corresponding brightened colours.
In particular it is advantageous for the converter to precedq
the ~mage store in which the second code words can ~e stored in
placc of the first code words. Another possibility consists
in that the converter is arranged between the image store and an
ima~ repetition store. The image repetition stoxe need not
contain the content o one entire page. For example it can be
sufficient for the image repetition store to store the content
o only one line.
A high degree of legibility o~ the chaxacters can a~so
be achieved in that the display unit represents characters with
an increased image frequency and that chara~ters in the
relatively dark colours are represented more frequently than
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characters in the relati~el~ ht c~lou~s,~ or in th~t the contxol
unit supplies the, display unit ~th signals which periodically
temporarily block the brightness signals in tha case of the
representation of characters in relatively light colours.
Especially in the case of the use o a flat screen on
which representation takes place using a plurality of light points,
it is'advantageous for the con~rol unit to generate signals which
trigger representation involving more light points~o~ the display
unit in the event of the representation of characters' in the
io relatively dark colours than in the case of the representation
of characters in the relatively light colours.
The control arrangement is advantageously used whenever
in particular the basic colours blue and red are provided as
relatively dark colours and in particular the colours white, yellow
and cyan are provided as relatively light colours.
As the brightness of characters having the basic colours
blue and red also differ, it is advantageous for the control unit
to produce slgnals by means of which the basic colour blue is
b~ightened more than the basic colour red in comparison to the
20 r~latively light colours.
It proves particularly expedient to employ the arrangement
when alphanumexical characters and/or linear graphic symbols are
providQd b~ way of characters.
The use of the arrangement is advantageous not only for
the representation of videotex pages which contain exclusively
characters or mixed representations of characters and graphic
patterns, but the use of the arrangement also proves expedient
for the relative brightening of the comparatively dark colours
when characters are'to be gated into a television picture.
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~ particularl~ ~d~antageous representation of the
characters on the screen is achieved i~ the xelati~e bri~htening
of the comparatively dark colours takes place only in cases where
thexe is a dar~ background colour to the characters.
The invention will now be described with reference to the
drawingsr in which:-
Figure 1 schematically illustrates an extract from an
exemplary videotex page;
Fi~ure 2 is a bloc~ schematic circuit diagram illustrating
IO a irst exemplary embodiment of a control arrangement constructed
in accordance with the inventlon;
Figure 3 is a block schematic circuit diagram illustrating
a second exemplary embodiment of a control arrangement; and
Figure 4 is a blocX schematic circuit diagram illustrating
a third exemplary embodiment of a control arrangement.
In the extract from a videotex page represented in Figure 1,
typical characters AZ, symbols GZ and a graphic pattern GM have been
represented~ The alphanumeric characters AZ and graphic symbol
( ' GZ are composed of fine lines, and both are arran~ed, together
with the graphic pattern GM, in an assembly of character arrays
ZF, the boundaries of which have been shown ~or purposes o~
explanation, but are not normally visible on the display screen.
Fo~ the representation of characters or symbols, each character
array ZF in this example is divided into an invisible grid
comprising 8x12 image points BP. The characters AZ are represented
on the screen by virtue of the differing degress of brightness of
the image points BP. The graphic symbols GZ can be represented
ln a similar manner to the alphanumeric characters AZ, but one
symbol can extend over a plurality of character arrays ZF. The
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characters AZ and s~bols GZ can be repre~ented in the three
basic colQu~s ~ ~ed~ ~een ~ bluel ~he ~ixed c~lour~ Qf yellow;
cyan or magenta, and in black or ~hite~ but within an~ one
character array ZF the colour cannot change. Any of the basic
colours, mixed colours or black and white can be used as a
background colour.
In the case of the representation of the graphic patterns
GM, the chaxacter arrays ZF are divided into 2x3 gr?phic elements
GE. The graphic patterns GM are then represented in character
arrays ZF with different combinations of the graphic elements GE.
The~graphic elements GE and the background colour can be
represented in any basic colour, mixed colour, or black or white.
If the representation of the characters AZ and s~mbols
GZ on the screen takes place in relatively dark colours such as
red or blue, then particularly if there is a dark background there
is a danger that the characters AZ or s~mbols GZ will be dificult
to read. This will be particularly so when, as illustrated in
Figure 1, a graphic pattern GM in a relatively light colour such
as white, yellow or cyan extends very close to characters AZ or
~0 s~mbols GZ in blue or red, for example.
Furthermore, it has been ascertained that in the case of
the pure representation of characters these are difficult to
read whe~ part of the videotex page is occupied by characters
in a relatively light colour and a further offset part of the
2S page is filled with a relatively dark colour.
In the first embodiment of control arrangement,
illustrated in Figure 2, a control unit SE is axranged between an
image control unit BST and a display unit AE provided with a
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screen ~not shown~. The ima~e control unit ssT is o~ known
design, and contains s~itch~o~er units ~ia.~hlch coloux si~nals
emanating from a television receiver or f~om a videotex decoder
are selectively switched through t~ the display unit AE. Switch-
over units of this kind are generally known, and are described,for example, in the magazine "Wireless World", May 1976, pages
64-68.
The colour signals R, G and B assigned to the basic colours
,~ red, green and blue are supplied to the display unit AE via delay
ele.ments V. The colour signals R, G and B are also supplied to
the'control unit SE. In the case of the representation of
television pictures on the display unit AE! the colour signals
consist of analogue-signals whose instantaneous values deter~;ne
the colou.rs to be represented and the brightness thereo. In the
case of the representation of characters, symbols and graphic
patterns, the colour signals consist of binary signals which
assume the binary values "0" or Illn. In the case of the
representation of the colour red, for example, only the colour
( signal R possesses the binary value "1"'. Similarly in the case
o the representation of the colours blue or green, onl~ the
colour signal B or G respectively possesses the hinary value "1".
The colour black is represented when all the colour signals have
the binaxy value "0", and for representation of the colour white
all the colour signals possess the binary value "1". The mixed
colours o yellow, cyan and magenta are represented when two of
the colour signals R and G, G and B, or R and B, respectively
each possess the binary value "1".
When the videotex decoder establishes that a videotex
page is to be represented, the corresponding colour signals R,
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G and B are ~ed to the display unit AE. In the case of the
representation o~ the gra~hic pattexns G~ ~nd the Xepresentation
of the background colours~ the colour signals ase ~ed in known
manner to the display unit AE. In the case o~ the representation
of alphanumeric characters AZ or graphic symbols GZ, the image
control unit BST produces corresponding signals SAZ or SGZ
respectively. When one of these signals occurs, an OR-gate Gl
in the control unit SE emits a signal Sl to two AND- gates, Ul
and U2. If the characters are to be represented in~blue, the
' 10 colour signal B has the binary value "1" whereas the colour signals
R and G have the binary values "0". In this case the AND-gate
Ul emits a signal S2 via a switching stage SSl to cause an
analogue OR-gate G2 to feed a signal S3 to ~he display unit AE.
This signal S3 serves as a brightness signal, and is used to
cause the blue characters or symbols to be brightened in relation
to the relatively light colours such as white, yellow or cyan
The brightening can be effected in known manner in that, in the
display unit AE, small constituents of the basic colours, red and
green, are produced by corresponding additional colour signals.
It is also possible to supply the s~gnal S3 to the grid of a
pictur~ tube in the form of a cathode ray tube in order to increase
~he bxightness. In the case of representation o characters or
s~mbols in redr then in a slm; 1 ar manner to that used
~or xapresentation of charactexs or symbols in blue, these are
brightened by a signal S4 produced by means of the AND-gate U2.
The switching stages SSl and SS2 can be used tQ change the
amplitude of the signals S2 and of the signals S4 respectivelyr
and consequently adjust the signals S3 so that the basic colours
red and blue can be brightened to differing extents. Here it is
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particulaxly advant~geou~ the colour blue t~ be brightened
more than the colour ~ed The delay ~lements ~ are provided to
compensa~e for the additional transit times which occur in the
AND-gates Ul and U2 r the switching stages SSl and SS2, and the
OR-gate G2~ so that the signals S3 are presented simultaneously
to the correspondins colour signals.
The control unit SE provides that, in the event of the
representation of cha~acters in the relatively dark~colours of
red and blue, these can be brightened relative to the comparatively
li~ht colours in a simple manner.
' This relative brightening of the comparatively dark colours
can be effected in that the display unit A~ is desi~ned for a
higher picture frequency and in that the characters AZ and symbols
GZ of relatively light colours are represented at a lower
picture frequency than the characters AZ and GZ of relatively
dark colours. In this case the signal S3 sets a higher picture
~requency so that then the relativel~ dark colours appear brighter.
If the screen is one component of a plurality of light
points, and for example is a flat screen, the relative brightening
o~ the comparativel~ dark colours can be efected in that the
comparatively light colours are represented with a smaller number
o~ light points whereas the signal S3 provides that
correspondingly morQ.light points are used to represent
characters or symbols in the comparatively dark colouxs.
In the alternative control arrangement illustrated in
Figuxe 3, the relative brightening of the comparatively dark
colours is achieved in representation of videotex pages by
increasing the overall brightness, and in the case of the
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representation o~ graphic patterns~ GM ~r of background colours
the com~aratively light colours are selectively darkened~
A videotex decoder in the image control unit BST emits the colour
signals R, G and B and the signals SAZ and SGZ to multiple
inputs of a control unit SE~ For representation of graphic
patterns GM or of background, the signals SAZ and S~Z each have
the binary value "0", so that three AND-gates U3 and U5 are
released. If the graphic pattern GM or the background colour
~, i9 to be represented in white, yellow or cyan, the AND-gates,
U3, U4 or U5, as the case ma~ be, emit a signal S5, S6 or S7
res~ectively, which is fed via a switching stage SS3, S54 or
SS5 respectively, and thence via an analogue OR-gate G3 to form a
signal S8 that is f~d to the display unit AE, and darkens these
colours, so that in this way the relatively dark colours appear
brlghter relative to the comparatively light colours. The delay
elements V are provided in order to compensate for the delay
times resulting from the AND-gates U3 to U5, the switching stages
SS3 to SS5 and the OR-gate G3. The switching stages SS3 to SS5 can
serve to individually adjust the degree of darkening for each
colour. The signal S8 is expediently conducted to the grid of the
o~thode ray tube in order to reduce the brightness of the
corxeqpondinq colours.
If representation may take place on the display un~t screen
at an increased picture frequency, the signal S8 can be used to
reduce the picture frequency in the case of repres~ntation of
relatively light colours, so that here too the relatively dark
colours appear brighter. In the case of representations composed
of a plurality of light points on a flat screen, the signal S8 can
be used to reduce the number of operated light paints in the case
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of the representation o~ xelatiYel~ light colours.
~ nother possibility o~ selectively darkening the xelati~elylight colours involves using tlle signal S8 to make ~he
corresponding brightness signal intermittent, i.e. to periodically
temporarily interrupt the relevant colour signal. This c n be
effected by an AND logic-linking element having one input
connected to a clock pulse train signal emitted from an oscillator,
~or ~mrle. ~
~, In the further alterna~ive control arrangement represented
by the block circuit diagram illustrated in Figure 4, the control
un~t SE itself forms part of the image control unit BST. As
regards the videotex decoder, only an image store BSP has been
shown, which stores-data words assigned to the characters, symbols
and graphic patterns which are to be represented. For ~mpl e
these data words contain 16 binary characters, of which 8 are
assigned to the alphanumeric characters A~ or graphic elements OE
which are to be represented, and of which a further 8 binary
characters represent control signals which characterise the colour
( or the nature of the representation or which indicate that it is
a matter o~ data words which are assigned to the alphanumeric
characters A~ or the graphic elements GE. First code words composed
o three ~inary characters in accordance with the colour signals
R, G and B are provided for the representation of the colours.
The control unit SE contains an image repetition sto~e BWS
which in this example intermediately stores the content of one row
on the screen. With the exception o~ the first code words which
are assigned to the colour signals~ all the other binary characters
are directly conducted, as signals S9r to the im~ge repetition store
BWS. The colou~ si~nals a~e fed to the im~ge repetition store
BWS ~ia ~ conve~tex U~l~
The image repetition store BWS contains ~ore storage
positions for data words than the image store BST. In place of
three binary characters for the first code words, four binary
cha~acters for second code wsrds are provided in the data words r
so that in addition to the basic colours, the complementary
colours thereto and biack and white, still more colours can be
stored. For example the colours "bright blue" and "bright red"
are provided by way of further colours. ~hen the videotex decoder
emits the signals SAZ or SGZ and characters or symbols are to be
represented in red or blue, the corresponding combinations of
the binary characters which are.assigned to these bright colours
are stored in tne second code words within the image repetition
~tore BWS. The image repetition store BWS is followed by a second
converter UM2 which assigns three colour signals, R1, G1 and B1
to these four binary characters. These colour signals differ from
the colour signals R, G and B in that, in.the case of the
representation o the characters in blue, the colour signals Rl and
20 ~1 al30 possess glven instantaneous values, and that in the
repr~sentation of the characters in red, ~he colour signals Gl and
~1 ~lso possess given instantaneous value, in order to brighten
the blue and red on the basis of the additive mixing of the colours.
In another possible design of the image control unit the
image store BSP is extended to the extent that second code words
formed from four binary characters are provided for the coloursO
In this case the image repetition store BWS is not required and the
converter UMl i~ connected preceding the Lmage StQre BSP.
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The conyeXteX U~2-can also be designed in such m~nner
that, as illustrated in ~igures 2 ~nd 3r it ~roduces additional
brightness signals corresponding to the signals S3 or S8, in
order to operate the grid of the picture tube, or to change the
S picture frequency, or vary the number of light points operated
on a flat picture tube.
The converter U~l can be designed to forward the colour
signals R, G and B unchanged to the Lmage xepetitl~n store BWS
~, for the representation of characters or symbols. This can be the
case, for example, when the ~haracters or symbols are represented
on ~ light background. For this purpose the converter UMl can
contain a store in which the background colour wnich applies to the
character array in question is intermediately stored, and the
brightPni ng of the relatively dark colours can take place in
dependence upon the contents of said store. An inte ~ te store
of this type can also be provided in the control arrangements
described with reference to Figures 2 or 3, so that also in this
case the relative brightening of the relatively dark colours takes
place only when these are represented on a dark background.
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