US 5,394,217 AGranted

Method and apparatus for determining line frequency and detecting variable frequency light sources

AssigneeEastman Kodak Company

InventorsMichael J. Gaboury, J. David Cocca

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Abstract

A line frequency is determined by interleaved sampling of ambient light to obtain analog voltage samples at predetermined sampling rates associated with two or more line frequencies. Where there are two line frequencies, one method separates the first samples by a time period at least equal to an analog-to-digital conversion time, and less than the earliest time when a sample associated with one line frequency would coincide with a sample from the other. There are n samples per flicker frequency period and Q samples for each line frequency are taken. In a second method, a first common sample is taken for all line frequencies, and a condition characterized by simultaneous samples for different line frequency sample groups triggers a common sample for all line frequencies. For both methods, digital sample values one through Q-1 for each group are operated on to obtain a result, and then two through Q are similarly operated on to obtain a second result. The result for samples one through Q-1 for a given line frequency is compared to the result for samples two through Q. If the results for a given line frequency are within a predetermined limit, the presence of that line frequency is indicated. The known line frequency can be used to set the light sampling rate for exposure setting, as well as imprinting light source information onto photographic film.

Claims29

Dependent claims

A method for determining the presence of a line frequency from a group of possible line frequencies, said group of possible line frequencies comprising a first line frequency having an associated first flicker frequency period and a second line frequency having an associated second flicker frequency period, said first line frequency being lower than said second line frequency, said method comprising the steps of:

sampling ambient light to obtain a first analog voltage sample representative of ambient light level for a first sample group and converting same to a digital value, wherein said first sample group corresponds to said first line frequency and consecutive analog voltage samples for said first sample group are taken at a first sample rate;
sampling said ambient light to obtain a first analog voltage sample representative of ambient light level for a second sample group after a predetermined time from said first analog voltage sample of said first sample group and converting same to a digital value, wherein said second sample group corresponds to said second line frequency and consecutive analog voltage samples for said second sample group are taken at a second sample rate, said first sample rate and said second sample rate being defined by the following:
sample rate=1/(f.sub.f X n),
where
f.sub.f =flicker frequency in Hertz, and
n=number of samples per flicker frequency period,
and wherein said predetermined time is at least equal to a time required for said converting and less than a shortest time wherein a future sample for said first sample group would coincide with a future sample for said second sample group;
sampling said ambient light at said first sample rate to obtain a second analog voltage sample for said first sample group and converting same to a digital value;
sampling said ambient light at said second sample rate to obtain a second analog voltage sample for said second sample group and converting same to a digital value;
repeating said steps of sampling and converting for said first sample group and said second sample group until a predetermined number of samples Q are taken and converted therefor;
and
comparing converted samples in at least one sample group to determine if a presence of said line frequency is indicated.

9 more elements

A method for determining the presence of a line frequency from at least two possible line frequencies, each line frequency having an associated flicker frequency period, said method comprising the steps of:

sampling ambient light to obtain a common first analog voltage sample representative of ambient light level and converting same to a digital value for at least two sample groups, each of said at least two sample groups being associated with a different one of said at least two possible line frequencies, wherein consecutive samples for a given one of said at least two sample groups are taken at a sample rate defined by the following:
sample rate=1/(f.sub.f X n),
where
f.sub.f =flicker frequency in Hertz, and
n=number of samples per flicker frequency period;
repeatedly sampling ambient light to obtain analog voltage samples representative of ambient light level and converting same to digital values for each of said at least two sample groups at the respective sample rate until a predetermined number of samples Q are taken and converted therefor;
determining a presence of a condition characterized by said sampling for more than one of said at least two sample groups coinciding;
sampling said ambient light to obtain a common analog voltage sample and converting same to a digital value for each of said at least two sample groups in response to said determined presence of said condition;
and
comparing converted samples in at least one sample group to determine if a presence of said associated line frequency is indicated.

7 more elements

A line frequency determination device for determining the presence of a line frequency from a group of possible line frequencies, said group of possible line frequencies comprising a first line frequency having an associated first flicker frequency period and a second line frequency having an associated second flicker frequency period, said device comprising:

means for sampling ambient light, each sample being associated with a sample group corresponding to one of said group of possible line frequencies, wherein consecutive samples in a given sample group are taken at a sample rate defined by the following:
sample rate=1/(f.sub.f X n),
where
f.sub.f =flicker frequency in Hertz, and
n=number of samples per flicker frequency period,
and wherein consecutive samples for different sample groups are interleaved;
means for generating an analog voltage sample representative of ambient light level;
means for converting said generated analog voltage sample to a digital sample, said converting means requiring a conversion time for converting a given analog voltage sample;
means for staggering for a predetermined time a first sample for a first sample group corresponding to said first line frequency and a first sample for a second sample group corresponding to said second line frequency, wherein said predetermined time is at least equal to said conversion time and less than a shortest time where a future sample for said first sample group would coincide with a future sample for said second sample group;
and
means for comparing digital samples to determine if a presence of a given line frequency is indicated.

8 more elements

Dependencies are inferred from the claim text.