Method and system for detecting flicker
An image processing system includes a plurality of active pixels and a plurality of flicker pixels. The active pixels output active pixel signals at a first readout frequency, and the flicker pixels output flicker pixel signals at a second readout frequency greater than the first readout frequency. A plurality of frequency detectors accumulate the flicker pixel signals and then perform frequency domain transformation of the accumulated flicker pixel signals. A frequency analyzer detects flicker by analyzing the flicker pixel signals which have been transformed into the frequency domain.
1. An image processing system comprising:
a plurality of active pixels to output active pixel signals at a first readout frequency;
a plurality of flicker pixels to output flicker pixel signals at a second readout frequency greater than the first readout frequency;
a plurality of frequency detectors to accumulate the flicker pixel signals and to perform frequency domain transformation of the accumulated flicker pixel signals; and
a frequency analyzer to detect flicker by analyzing the flicker pixel signals transformed into the frequency domain, wherein each of the frequency detectors is to:
detect a dominant frequency among the flicker pixel signals transformed into the frequency domain, and
calculate a confidence value indicating how the dominant frequency is different from remaining frequencies of the flicker pixel signals transformed into the frequency domain, the frequency analyzer to detect flicker based on the confidence value to be calculated by each of the frequency detectors.
2. The system as claimed in claim 1 , wherein the frequency analyzer:
determines whether the confidence values are greater than a minimum confidence value, and
detects flicker when at least two of the confidence values are greater than the minimum confidence value.
3. The system as claimed in claim 1 , further comprising:
an image sensor including the active pixels and flicker pixels, and
an image signal processor including the frequency detectors and the frequency analyzer.
4. The system as claimed in claim 1 , further comprising:
an image sensor including the active pixels, the flicker pixels, the frequency detectors, and the frequency analyzer.
5. The system as claimed in claim 1 , wherein:
the flicker pixels are located in a first region, and
the active pixels are located in a second region which does not overlap the first region.
6. The system as claimed in claim 1 , wherein the flicker pixels are located between the active pixels and wherein the active pixels are to output signals to generate an image independently from output signals of the flicker pixels.
7. The system as claimed in claim 1 , further comprising:
a row driver to apply row selecting signals to the active pixels, the row selecting signals applied at the first readout frequency to read out the active pixel signals, the row driver to apply flicker selecting signals to the flicker pixels, the flicker selecting signals applied at the second readout frequency to read out the flicker pixel signals.
8. A method for detecting flicker in an image processing system, the method comprising:
accumulating flicker pixel signals output from flicker pixels;
performing frequency domain transformation for the accumulated flicker pixel signals;
detecting a dominant frequency among the flicker pixel signals transformed into the frequency domain;
calculating a confidence value indicating how the dominant frequency is different from remaining frequencies of the flicker pixel signals transformed into frequency domain; and
detecting flicker based on the confidence value for the flicker pixel signals transformed into the frequency domain, wherein the active pixels output active pixel signals at a first readout frequency, and the flicker pixels output the flicker pixel signals at a second readout frequency greater than the first readout frequency.
9. The method as claimed in claim 8 , further comprising:
applying row selecting signals corresponding to the first readout frequency to the active pixels to output the active pixel signals; and
applying flicker selecting signals corresponding to the second readout frequency to the flicker pixels to output the flicker pixel signals.
10. The system as claimed in claim 1 , wherein the confidence value is based on a standard deviation of the flicker pixel signals relative to the dominant frequency.
11. The system as claimed in claim 1 , wherein the frequency analyzer is to detect local flicker based on confidence values corresponding to flicker pixel signals output from N flicker pixels, where N is less than all the flicker pixels.