Legibility for alpha-mosaic characters

Details Legibility for alpha-mosaic characters Legibility for alpha-mosaic characters

1981-02-27

1982-11-09

Martin, John C.

Facsimile and static presentation processing

Static presentation processing

Attribute control

358 37, 358 39, 358147, 340701, 340748, 340723, 340793, H04N 9535, H04N 514, G09G 116, G09G 128

Patent

active

043587887

ABSTRACT:
In add-on alpha-mosaic character (teletext) decoders, the character signals pass through the limited bandwidth chroma channel of the TV receiver. For certain color combinations and signal durations this reduces legibility and contrast due to pulse stretching and amplitude reduction. The present invention determines if a pulse is less than a predetermined pulse width and has an amplitude difference with respect to a preceding pulse of less than a selected amount. If both conditions are met, then a luminance signal pulse is generated to substitute for the original pulse, the generated pulse having a large amplitude difference with respect to the preceding pulse for improved contrast. If the generated pulse would exceed the white level or go below the black level, then a pulse of opposite polarity with respect to the first generated pulse is generated to cancel the first generated pulse but still result in a large amplitude difference with respect to the preceding pulse.

REFERENCES:
patent: 4212008 (1980-07-01), Hopkins
patent: 4314245 (1982-02-01), Wilbur

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