Method of and apparatus for processing picture signal

A picture signal processing method employed in a digital still camera, the digital camera using an interlaced scanning type CCD, when a subject is sufficiently bright and a still picture is recorded in a frame period same as that of monitoring, the method comprising:

• calculating an OB level difference correction amount at the time of readout of the still picture based on an OB level difference correction value immediately before recording, a rate of occurrence of dark current in the pixel section of the CCD and in a vertical transfer section, a frame period, and an actual exposure time in the frame period.

A picture signal processing method employed in a digital still camera, the digital camera using an interlaced scanning type CCD, when a subject has low luminance, and at the time of still recording when exposure is performed over several frames, and when an OB level difference correction value calculated in a monitoring mode immediately before recording is calculated, a gain multiplied before entering into the signal processing apparatus is taken into consideration, and the OB level difference correction amount is multiplied by a negative gain, and further by the number of exposure frames, and this value is designated as the OB level difference correction amount at the time of readout of the still image.

A picture signal processing apparatus comprising:

• an OB level difference correction circuit which calculates an OB level difference from the luminance signal levels of at least two frames which are exposed for proper exposure time and for exposure time different from the proper exposure time, the OB level difference being a difference in black level, which is a difference between an optical black level, being en electrical output level when there is no optical input with respect to a two-dimensional CCD image pickup device, and a black level of a picture signal, and corrects the OB level difference in an input step of a signal processing circuit.

A picture signal processing apparatus in a digital still camera using an interlaced scanning type CCD, having an OB level difference correction circuit which calculates an OB level difference correction amount at the time of reading a still picture, from the OB level difference correction value immediately before recording, a rate of occurrence of dark current in the pixel section and in a vertical transfer section of the CCD, the frame period, and the actual exposure time in the frame period, when a subject is sufficiently bright, and the still picture is recorded in a frame period same as that of monitoring.

A picture signal processing apparatus in a digital still camera using an interlaced scanning type CCD, having an OB level difference correction circuit which takes a gain multiplied before entering into the signal processing apparatus into consideration, when calculating an OB level difference correction value calculated in a monitoring mode immediately before recording, multiplies the OB level difference correction amount by a negative gain, and further by the number of exposure frames, and designates this value as the OB level difference correction amount at the time of readout of the still image, when a subject has low luminance, and at the time of still recording when exposure is performed over several frames.