Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-12-27
2004-12-07
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S214100
Reexamination Certificate
active
06828539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and device for correcting a detection signal output from a solid-state detector, as well as a solid-state detector having a correcting capability for use therewith, and more specifically, to a device and a method for correcting an image signal or other signal which is output from such a solid-state detector as a solid-state image sensor, including a CCD image sensor which detects visible light and outputs an image signal, and a radiation solid-state detector which detects radiation and outputs an image signal, and a solid-state detector having this correcting capability.
2. Description of the Prior Art
Up to now, solid-state image sensors such as a CCD image sensor, which detects visible light and outputs an image signal, have been widely used in such applications as video cameras and digital still cameras. This solid-state image sensor comprises a number of photoelectric transducers disposed in the form of a matrix (for color applications, a color filter is further overlaid upon each photoelectric transducer) outputting an image signal (consisting of pixel signals each representing the signal value of each pixel) carrying a visible image as two-dimensional matrix information.
Nowadays, in the field of radiation photography for medical diagnosis, a variety of radiation solid-state detectors (mainly consisting of a semiconductor, and hereafter may be simply called “detectors”), which detect radiation in a form of latent electric charges of an amount corresponding to the dose of the radiation to which the detectors have been exposed and record the radiation image in a form of an electrostatic latent image and output an image signal carrying the recorded electrostatic latent image, have been proposed and put to practical use. As a typical one of the various types of radiation solid-state detectors proposed, the radiation solid-state detector of photoelectric conversion type, which reads out the stored charges (also called the “latent image charges”) carrying image information by means of thin film transistors (TFTs), a direct conversion type and an improved direct conversion type, a mode of the direct conversion type (also called “light reading type”) wherein the reading light is projected for scanning and reading out the latent image charges, are available. These types will be explained in the section titled “DESCRIPTION OF THE PREFERRED EMBODIMENTS”.
With any one of the above-mentioned various types of radiation solid-state detectors, the solid-state detecting elements are disposed in the form of a matrix, and the output is an image signal (consisting of pixel signals each representing the signal value of each pixel) representing a radiation image as two-dimensional information.
Hereinbelow, a solid-state image sensor which detects visible light and outputs an image signal representing a visible image as two-dimensional matrix information and a radiation solid-state detector which detects radiation and outputs an image signal representing a radiation image as two-dimensional matrix information are collectively referred to as “solid-state image detectors.” When a solid-state image detector can output not only two-dimensional, but also one-dimensional information, it is referred to as a “solid-state detector” . A variety of elements, such as the photoelectric transducer constituting a solid-state image sensor and the solid-state detecting element constituting a radiation solid-state detector (described later) are collectively called “detecting elements”.
With the detecting elements constituting a solid-state image detector as stated above, the characteristic of quantity of incident light or dose of incident radiation versus output signal value (hereafter called the “input-output characteristic”) varies from element to element, and if uniform radiation or light (hereafter generically called “uniform radiation”) is projected on the entire surface of the solid-state image detector, the image signals output from the detecting elements constituting the solid-state image detector will have variations.
The variations in input-output characteristic results from various factors, such as the variations in the sensitivity of the detecting elements, variations in load capacity of the detecting elements, and variations in the gain and offset voltages of the output amplifiers connected to the detecting elements to output the detected image signals. Also, these variations cause the image signals to have noise, and if image output is carried out on the basis of the image signals having such variations, the output image will include noise and have a deteriorated image quality.
To correct these variations of the image signals, methods for correcting the image signals output from a solid-state image detector have been proposed (for example, Japanese Unexamined Patent Publication No. 7 (1995)-72256).
With this image signal correcting method, the correction is made for each of the detecting elements (the solid-state light detecting elements) constituting a radiation solid-state detector (or for each group of elements comprising a set number of detecting elements) so that the values of the image signals when radiation is not projected (hereafter called “in the dark state”) is nullified. When the correction values for the image signals when uniform radiation is projected so that the detecting elements are irradiated with an equal dose of radiation (hereafter called “in the bright state”) that is approximately the same for all the detecting elements (or the groups of elements) are determined, the output image signals from the radiation detector are corrected based on these correction values. Also, the offset correction values, for correcting so that the values of the image signals in the dark state are nullified, and the gain correction values, for correcting so that the image signals in the bright state are approximately the same for all the detecting elements (or the groups of elements), are used as the correction values in the correction. Thus, this method to be used suppresses the noise which would be included in the image signals, allowing a high-quality radiation image to be output.
However, with the above-mentioned signal correcting method, the specification only states that the correction is made so that the values after the correction in the bright state are roughly uniform for all the detecting elements (or the groups of elements). The specific value that is to be selected is not stated. Depending upon the value, a problem may occur in that, when radiation having a dose of radiation that would saturate the detecting elements is projected onto all of the detecting elements, the value for one pixel is transformed into a maximum value which can be taken after the correction, while that for another pixel is transformed into a value less than the maximum, resulting in the image signals after the correction having variations. In other words, the correction made is insufficient.
For example, assume that the image signal of a detecting element “a”, which has an image signal value of 50 in the dark state and an image signal value of 800 in the bright state, and the image signal of a detecting element “b”, which has an image signal value of 30 in the dark state and an image signal value of 900 in the bright state, are corrected in accordance with the correcting method of the reference cited. It is also assumed that the saturation values of either of the output image signals from the detecting elements “a” and “b” is 1000, and the maximum value which can be taken after the correction is also 1000.
First, the offset correction is made so that either of the image signal values in the dark state is nullified. On the other hand, it is assumed that the gain correction is made so that both of the values after the correction in the bright state are 800, in other words, the image signal of the detecting element “a” is transformed from 800 to 800, and the image signal of the detecting element “b” is transformed from 9
Fuji Photo Film Co. , Ltd.
Le Que T.
Sughrue & Mion, PLLC
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