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Browse Prior Art Database

Gray Scale to Pseudo Halftone Conversion

IP.com Disclosure Number: IPCOM000088374D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Mix, AL: AUTHOR [+2]

Abstract

Devices employing single, discrete size print elements, such as ink jet drops and wire printers, must print grays by deposition of a proportion of possible print positions within a small area.

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Gray Scale to Pseudo Halftone Conversion

Devices employing single, discrete size print elements, such as ink jet drops and wire printers, must print grays by deposition of a proportion of possible print positions within a small area.

In Fig. 1, a video signal 10 representing gray scale information from scanner 11 is compared to a high frequency waveform 13 in device 12. The waveform is generated by oscillator 14 and shaping circuit 15. The comparison between the shaped high frequency waveform 13 and the video signal 10 results in a two level pulse waveform 16 of the frequency of oscillator 14, pulse-width modulated by the video amplitude.

The frequency of the pulse-width modulated signal 16 is significantly higher than the rate of operation of print element 17. Thus, the high frequency signal 16 is sampled by the lower frequency print element at times 18. The probability that the print element will be operated or not depends upon the pulse width and thus upon the level of the video signal, as shown in Fig. 2.

The shape of waveform 13 can be manipulated to control the gamma, or contrast function, between scanning and printing. In Fig. 2, the slope of the wave 13 is the printer gamma.

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