1. Field of the Invention
The present invention relates to an image pickup apparatus that picks up an image by using a solid state image pickup device.
2. Description of the Related Art
In recent years, image pickup apparatuses using solid state image pickup devices have been widely used in various apparatuses including the case of medical endoscopes.
In the case of a medical endoscope that is inserted into a body cavity, it is necessary to achieve diameter reduction to reduce a pain given to a patient by reducing an outside diameter of an insertion portion that is inserted into the body cavity, and it becomes necessary to reduce a size of a solid state image pickup device that is disposed in a distal end portion of the insertion portion.
In order to reduce the size of the solid state image pickup device which is disposed in the distal end portion of the insertion portion, it is conceivable to configure some pixels at a peripheral side of pixels forming a light receiving portion to have a configuration of effective pixels having no optical black pixels (OB pixels) that generate signals of black levels on an picked-up image by mechanically blocking light from reaching some pixels at the peripheral side of the pixels forming the light receiving section.
Although it becomes possible to reduce the size of the solid state image pickup device which is disposed in the distal end portion of the insertion portion by adopting the solid state image pickup device having no OB pixels in this way, the black levels on the picked-up image is in an indefinite state by adopting the configuration having no OB pixels, and the entire image becomes white (black floating) or becomes unnatural black (black sinking) on monitor display, so that a circuit configuration that generates signals of black levels is needed.
For example, Japanese Patent Application Laid-Open Publication No. 2007-019577 as a first prior example discloses an image pickup apparatus including a mechanical shutter configured to capture an object optical image, an image pickup device configured to output an image signal based on the object optical image incident through the mechanical shutter, storage means configured to hold the output from the image pickup device in a light shielding state time by the shutter as a dark output, and correction means configured to estimate noise components in an actual photographing time based on an exposure time period at the actual photographing time at which the object optical image is captured through the mechanical shutter, and the dark output stored in the storage means, and remove the estimated noise components from the output of the image pickup device at the actual photographing time to output the output of the image pickup device.
Further, Japanese Patent Application Laid-Open Publication No. 2014-82698 as a second prior example discloses an image pickup apparatus including an image pickup device capable of acquiring a first photographed image and a second photographed image in one image output period, image judging means configured to judge whether or not to acquire an image for dark shading correction in accordance with photographing conditions, image acquisition means configured to acquire the image for dark shading correction instead of the second photographed image when the image judging means judges to acquire the image for dark shading correction, and image correction means configured to correct the first photographed image and the second photographed image by using the image for dark shading correction.