Digital densitometer with lut output summation to yield...

Details Digital densitometer with lut output summation to yield... Digital densitometer with lut output summation to yield...

1998-11-04

2001-04-24

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C347S184000

Reexamination Certificate

active

06222176

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to density measurement devices and methods, and is particularly useful in imaging devices such as for example in electrostatographic reproduction apparatus.
BACKGROUND OF THE INVENTION
In the field of light measurement and densitometry, the need to convert from an electrical voltage proportional to light intensity to another signal proportional to optical density has long been recognized. One approach in the prior art has been to obtain a sensor voltage signal representing intensity of transmitted or reflected light and convert this analog signal to digital form. The digital value is then used to enter a stored LUT of intensity and density values. The digital density value corresponding to the digital intensity value is read from the LUT.
U.S. Pat. No. 5,117,119 discloses an automatic gain selection electronic circuit, along with a second LUT to obtain high accuracy and resolution over an increased range of large densities. The first (or “base”) LUT contains density values corresponding to an analog-to-digital converter output for the lowest gain. The second (or “range”) LUT is much smaller than the first LUT and contains the relative density corresponding to each available gain. It provides the additional density output associated with the gain selected. The two LUT outputs are summed to obtain the actual density measurement.
The three ranges illustrated in U.S. 5,117,119 are divided by two threshold values in a 10:1 ratio. Thus two ranges have 10:1 max-to-min light or voltage input ratios, and the third range (used for lowest light intensities or highest density) may have arbitrarily small input light or voltage level. The illustration in U.S. Pat. No. 5,117,119 shows accuracy of 0.01 density units, but requires a 10-bit analog-to-digital converter to do so. In turn, the 10-bit analog-to-digital converter requires a large “base” LUT of 2
1
=01024 entries. A major limiting factor in accuracy is the analog-to-digital converter resolution. Worst-case density resolution for each range comes at the high-density (low light intensity) end of the range, where the analog-to-digital converter resolution, i.e., one count, corresponds to the largest density increment. U.S. Pat. No. 5,117,119 uses multiple analog threshold voltage levels for comparison to the light sensor voltage signal. Low levels of electrical noise and circuit variability could degrade the comparator accuracy and reliability for the low-voltage thresholds.
SUMMARY OF THE INVENTION
It is an object of the present invention to use more but smaller gain ranges (roughly 2:1 ranges in a preferred embodiment) and a particular scaling of the LUT density output that simplifies the summation of the “range” and “base” LUT outputs.
It is another object of the present invention to provide an improved automatic gain selection circuitry and a particular scaling of the LUT density output that simplifies the summation of the “range” and “base” LUT outputs.
It is yet another object of the present invention to provide the option to use “overlapping” nominal density ranges with hysteresis in the gain selection circuitry and a particular scaling of the LUT density output that simplifies the summation of the “range” and “base” LUT outputs.
According to a feature of the present invention, an auto-ranging densitometer includes a photodetector and an amplifier circuit adapted to produce an output signal proportional to intensity of light on the photodetector. The amplifier circuit has multiple gains that successively increase. An analog to digital converter converts the output signal of the amplifier circuit to digital format. A gain select logic outputs a gain code used to select the gain of the amplifier. A density signal generator circuit includes two LUTs, one of the LUTs being adapted to receive the output of the analog to digital converter and produce an output density scaled to include only low order bits; and the other of the LUTs being to receive the gain code and produce an output density scaled to include only high order bits. The outputs of the two LUTs are concantenation added to produce a summation density signal.


REFERENCES:
patent: 4473029 (1984-09-01), Fritz et al.
patent: 4546060 (1985-10-01), Miskinis et al.
patent: 4550254 (1985-10-01), Zomorrodi et al.
patent: 4673807 (1987-06-01), Kobayashi et al.
patent: 5065234 (1991-11-01), Hung et al.
patent: 5117119 (1992-05-01), Schubert et al.
patent: 5649266 (1997-07-01), Rushing

Affiliated with

Also associated with

Rating

Digital densitometer with lut output summation to yield... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Digital densitometer with lut output summation to yield..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital densitometer with lut output summation to yield... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2550633