Color television receiver with character display function

Details Color television receiver with character display function Color television receiver with character display function

1980-03-13

1982-11-30

Martin, John C.

Facsimile and static presentation processing

Static presentation processing

Attribute control

340701, 340793, 340723, 358 27, 358147, H04N 9535, H04N 920

Patent

active

043618502

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a color television receiver and, more particularly, to a current driver for use in association with a Teletext decoder designed for the Teletext system.


BACKGROUND ART

The Teletext system is an information broadcasting system in which Pages of text and graphical symbols are transmitted in coded form on otherwise unused television lines during the field interval. The decoded Pages are intended to be displayed in place of, or added to, the television picture. Newsflashes and Subtitles may be inset in the picture. According to the Teletext system as presented by the BBC's CEEFAX or IBA's ORACLE service, one of the otherwise unused lines of the television field-blanking interval is used to carry information for one Teletext Character Row. Such a line is referred to as Data-line.
At least one of the seven colors, white, yellow, cyan, green, magenta, red and blue, is used to depict the display character in the character rectangle. The background color which is filling the parts of the character rectangle not occupied by the character itself may be blank or any one of the seven display colors.
In displaying the pages, the operator may select a combination of colors for the display character and the background. Since the colors are established through a so-called additive color mixing system, the total driving current for every color is not the same. Therefore, in some color combinations, the brightness of the background results much brighter than the same of the display character, and vice versa, and, in such cases, it is difficult to distinguish the display character over the background.
Table 1 shows a driving current distribution for each of the seven colors.


TABLE 1 ______________________________________ Driving Current Color Red Green Blue Total on the driving driving driving driving screen current current current current ______________________________________ White 2 2 2 6 Red 2 2 Green 2 2 Blue 2 2 Yellow 2 2 4 Magenta 2 2 4 Cyan 2 2 4 ______________________________________ value, but merely shows the ratio of three driving currents. For example, white on the screen is established when the red driving current, green driving current and blue driving current are combined in a ratio of 2:2:2. Therefore, the total driving current for white amounts to 6. In another example, red on the screen is established when the red, green and blue driving currents are combined in a ratio of 2:0:0. Therefore, the total driving current for red amounts to 2. In the above examples, it would be quite difficult to distinguish red characters from the white background.


DISCLOSURE OF INVENTION

Accordingly, a primary object of the present invention is to provide a current driver for balancing the driving currents to render the total driving currents of all the colors to be approximately the same level.
In accomplishing this and other objects, a color television receiver has a decoder for producing red, green and blue driving currents in binary form in accordance with a received signal. The red, green and blue driving currents are applied to red, green and blue control circuits, respectively, for combining the red, green and blue colors on a screen of a cathode-ray tube in a combination defined by the received signal and for establishing one of a plurality of colors on the screen. The color television receiver according to the present invention is characterized in that a current driver is connected between the decoder and each of the red, green and blue control circuits for generating driving currents in a plurality of current components having different levels. The current components in one color driving current are combined with each other in a combination defined by the received signal for producing a predetermined level of color driving current, whereby the total current used for establishing each of the plurality of colors has the same level with each other.


BRIEF DESCRIPTION OF INVENTION

FIG. 1 is a block diagram

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