Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-13
2001-02-20
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140LS, C348S241000
Reexamination Certificate
active
06191408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a photosensor signal processing apparatus for suppressing a fixed pattern noise resulting from variations (unevenness) in characteristics of pixels of a metal-oxide-semiconductor (MOS) image sensor. More particularly, it relates to a photosensor signal processing apparatus for correcting the output of a MOS image sensor having an inflection point at which the output of each pixel changes from a linear function to a logarithmic function of incident illumination, and vice versa.
2. Description of the Related Art
In order to suppress a fixed pattern noise resulting from variations (unevenness) in characteristics of pixels of a MOS image sensor, one conventional approach has been directed toward improvements in the device fabrication process such that all of the pixel-forming devices of the MOS image sensor have uniform output characteristics.
In another conventional approach, a measurement is made in advance to determine characteristics of a pattern noise of the MOS image sensor. The fixed pattern noise is suppressed through a correction made subsequently on the basis of the predetermined pattern noise characteristics.
Japanese Patent Publication No. SHO 61-14702 discloses a method of correcting output variations between pixels of an image sensor. The output of this image sensor varies linearly with incident illumination. To correct the pixel-to-pixel output variation of the image sensor, individual output values “Did” from the pixels in a dark state and individual output values “Diw” from the same pixels in a bright state under uniform illumination are previously stored in a memory. An output value “D1” of each pixel, which is produced in response to light and shade of an image picked up by the image sensor, is corrected by arithmetic operation achieved in accordance with the formula: A(Di−Did)/Diw−Did) where A is a constant. With this arithmetic operation, the pixel-to-pixel output variation in the dark state and the pixel-to-pixel sensitivity variation (variations in the gradients of linear output characteristic curves) are corrected.
A solid-state imaging system disclosed in Japanese Patent Laid-open Publication No. HEI 5-30350 includes a charge-coupled device (CCD) having a mosaic of tiny pixels whose outputs vary logarithmically with incident illumination. To correct the pixel-to-pixel output variation, individual imaging data of the pixels are previously collected under uniform illumination, then stored in a memory. These pre-stored imaging data are subtracted pixel by pixel from individual imaging data of the pixels collected during actual imaging operation. With this subtracting operation, the pixel-to-pixel logarithmic output characteristic variation is corrected.
The output variation correcting method disclosed in the first-mentioned Japanese Publication cannot deal with the correction of variations in output of pixels having a logarithmic property. The solid-state imaging system shown in the second-mentioned Japanese Publication can achieve correction of the pixel-to-pixel logarithmic output characteristic variation. However, due to the subtracting operation, the intensity of corrected sensor output of the imaging system is lower than that of sensor output corresponding to actual incident illumination. The sensitivity of the overall imaging system goes down, accordingly.
Japanese Patent Laid-open Publication No. HEI 10-90058 discloses a MOS image sensor designed to produce a sensor output having both a linear function region and a logarithmic function region with respect to incident illumination. A problem associated with this known MOS image sensor is that at an inflecting point where the sensor output changes from the linear function to the logarithmic function, and vice versa, an output error resulting from the pixel-to-pixel characteristic variation (variations in characteristic of MOS transistors and photodiodes forming the pixels) is likely to increase.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a photosensor signal processing apparatus which can correct variations in characteristics between pixels of an image sensor having an inflection point at which the sensor output changes from a linear function to a logarithmic function of incident illumination.
According to the invention, there is provided a photosensor signal processing apparatus for suppressing a fixed pattern noise resulting from variations in output characteristics between photosensors of an image sensor, each of the photosensors having a linear function region in which sensor output varies linearly with incident illumination, and a logarithmic function region in which the sensor output varies logarithmically with incident illumination. The photosensor signal processing apparatus comprises a correction data storage device which stores a set of correction data about the respective photosensors for the correction of individual output values of the photosensors, and a correcting device for correcting each of the individual output values of the photosensors on the basis of a corresponding one of the set of correction data, so that the output values of the photosensors equal to one another.
With this arrangement, variations of the output characteristics between the photosensors are corrected such that all the photosensors have the same output characteristics which are identical to a standard output characteristic. Thus, a fixed pattern noise resulting from the pixel-to-pixel output characteristic variation can be suppressed.
In one preferred form of the invention, the correction data storage device includes a reference inflection point setting device for setting data about a reference inflection point between the linear function region and the logarithmic function region, and an inflection point data storage device which stores therein a set of data about individual inflection points of the photosensors. The correcting device includes an inflection point corrective calculation device for performing at least one corrective calculation on the basis of the reference inflection point data and the set of inflection point data so that the individual inflection points of the photosensors match with the reference inflection point. The reference inflection point setting device can set the reference inflection point data at any given value. The output characteristic at the inflection point of the photosensors can, therefore, be adjusted.
In another preferred form of the invention, the correction data storage device includes a reference offset data storage device which stores therein data about a reference offset common to all of the photosensors, and an offset data storage device which stores therein a set of data about individual offsets of the photosensors. The correcting device includes an offset corrective calculation device for performing at least one corrective calculation on the basis of the reference offset data and the set of offset data so that the individual offsets of the photosensors match with the reference offset. Thus, the pixel-to-pixel offset characteristic variation can be corrected.
Preferably, the photosensor signal processing apparatus further includes a linear characteristic correcting unit for correcting individual sensor outputs of the photosensors based on the reference offset data and the reference inflection point data so that within the linear function region, the individual sensor outputs have the same linear characteristics. Thus, the pixel-to-pixel output characteristic variation within the linear function region can be corrected.
It is preferable that the photosensor signal processing apparatus further includes a logarithmic characteristic correcting unit for correcting individual sensor outputs of the photosensors based on the reference inflection point data and data about a reference output at a given point within the logarithmic function region so that within the logarithmic function region, the individual sensor outputs have t
Imai Toshio
Shinotsuka Sukeyuki
Takebe Katsuhiko
Tanaka Toshiaki
Honda Giken Koygo Kabushiki Kaisha
Lee John R.
Lyon & Lyon LLP
LandOfFree
Photosensor signal processing apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photosensor signal processing apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photosensor signal processing apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586752