EP0333313A2
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EP
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Circuit for automatically adjusting the digitisation threshold of a reading signal for a digital image scanning device
Assignee: Olivetti SpA
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Filing: 1989-02-03
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Granted: —
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Expires: 2009-02-03
Abstract
Abstract The circuit defines the digitization threshold (V s ) in dependenced on the positive-peak and negative-peak signals previously received from the elements for scanning the pixels of the image, and in dependence on the analog signal (AS) of the pixel. The circuit comprises two detectors (21, 22) for respectively detecting a positive peak and a negative peak and which each have a short charge time constant and a long discharge time constant. A summing circuit (25) generates the threshold signal (V s ) as a linear combination of the signals (V max , V min ) of the detectors (21, 22), the analog signal (AS) of the pixel and a reference signal (V r ). Finally the threshold signal is compared (26) to the analog signal (AS) of the pixel to produce a binary reading signal.
Inventors
- 👤 Giuseppe Fogaroli
- 👤 Ennio Sgreccia
- 👤 Giorgio Tadini
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 15:26
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/403
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
107 words
A circuit for automatically adjusting the digitisation threshold of a reading signal for a digital image scanning device, comprising means (10) for scanning the pixels, capable of generating corresponding electrical reading signals and transmitting them in series to the adjusting circuit (17, 26) and memory means (14) controlled by the adjusting circuit (17, 26) for storing digital values of the signal in binary mode in dependence on the threshold, characterized in that the adjusting circuit (17, 26) defines the threshold (V s ) of the signal in dependence on the positive-peak (V max ) and negative-peak (V min ) signals previously received from the scanning means (10).
Claim 2
Dependent Claim
107 words
A circuit for automatically adjusting the digitisation threshold of a reading signal for a digital image scanning device, comprising means (10) for scanning the pixels, capable of generating corresponding electrical reading signals and transmitting them in series to the adjusting circuit (17, 26) and memory means (14) controlled by the adjusting circuit (17, 26) for storing digital values of the signal in binary mode in dependence on the threshold, characterized in that the adjusting circuit (17, 26) defines the threshold (V s ) of the signal in dependence on the positive-peak (V max ) and negative-peak (V min ) signals previously received from the scanning means (10).
Claim 3
Dependent Claim
36 words
A circuit according to claim 1, characterized by a positive-peak detector (21), a negative-peak detector (22) and combining means (25) for generating a linear combination V s of the signals detected by the detectors (21, 22).
Claim 4
Dependent Claim
35 words
A circuit according to claim 2, characterized in that the combining means (25) are arranged to generate the combination (V s ) also in dependence on the analog signal (V a ) of the pixel.
Claim 5
Dependent Claim
24 words
A circuit according to claim 3, characterized in that the combining means (25) operate in dependence on a predetermined reference signal (V r ).
Claim 6
Dependent Claim
45 words
A circuit according to claim 3 or 4, characterized in that the combining means (25) generate the threshold signal (V s ) to define, in dependence on the reading signal of each pixel, a binary signal which is capable of being stored in the memory.
Claim 7
Dependent Claim
34 words
A circuit according to claim 5, characterized in that the binary signal is generated by a comparator (26) with hysteresis, which compares the threshold signal (V s ) to the pixel reading signal (AS).
Claim 8
Dependent Claim
29 words
A circuit according to claim 7 characterized in that each of the detectors (21, 22) has a very short charge time constant and a much longer discharge time constant.
Claim 9
Dependent Claim
56 words
A circuit according to claim 7 characterized in that each of the detectors (21, 22) comprises a capacitor (C₁, C₂) having a charge time constant equivalent to the time for reception of the signals of a few pixels, the discharge time constant of each capacitor (C₁, C₂) being at least 200 times the charge time constant.
Claim 10
Dependent Claim
32 words
A circuit according to claim 8, characterized in that the positive-peak detector (21) has a discharge time constant of at least five times the discharge time constant of the negative-peak detector (22).
Claim 11
Dependent Claim
36 words
A circuit according to any of claims 5 to 9, characterized in that the combining means (25) produce an average of the peak signals, means (RV₂) being provided for experimentally varying the parameter of said mean.
Claim 12
Dependent Claim
22 words
A circuit according to claim 10, characterized by means (RV₁) for varying the parameter of the pixel signal in said combining means.
Claim 13
Dependent Claim
33 words
A circuit according to any of the preceding claims, characterized in that the detectors (21, 22) can be enabled by means (SW₁, SW₂) sensitive to the position of the pixels to be read.
References Cited (Backward Citations)
No citation records indexed.
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