1. Field of the Invention
The present invention relates to an image display apparatus for photographing an object by imaging devices and displaying the photographed image by a liquid crystal display and the like.
2. Description of the Background Art
In image display apparatus such as a video camera and a digital still camera, an image of an object is converted to an image signal by imaging devices, and the image signal undergoes an image processing to be displayed by a liquid crystal display and the like. FIG. 6 shows an example of a conventional image display apparatus. In FIG. 6, an imaging section 60 comprises, for example, CCD (Charge Coupled Device) imaging devices, converts an image of an object to an image signal and outputs the image signal to a signal conversion section 62. A white balance circuit 64 in the signal conversion section 62 adjusts the white balance of the image signal in response to a color temperature change. A gamma correction circuit 66 performs a processing to give a non-liniarity to the image signal.
Furthermore, in the case where the CCD imaging devices included in the imaging section 60 are color imaging devices having a color filter adopting the Bayer array or a G-stripe RB checkers array, an R-signal, a B-signal and a G-signal cannot be obtained simultaneously by the CCD imaging devices, so that if any processing is not performed, the image is displayed to be in a mosaic state. Accordingly, an interpolation processing circuit 68 in the signal conversion section 62 interpolates lacks of any of the R, B and G-signals by its interpolation processing.
When the pixels of the CCD imaging devices included either in a horizontal direction or in a vertical direction are different in number from those of a display section 76, an interpolation processing circuit 68 performs a thinning processing or an interpolation processing suitably using a memory circuit 70, whereby the number of pixels output from the CCD imaging devices is converted to be equal to that of the display section 76.
A gray scale correction circuit 72 in the signal conversion section 62 executes a gray scale correction such as a dither processing so that an image originated from the image signal processed looks better when it is displayed by the display section 76. A gamma correction circuit 74 performs a gamma correction for the image signal processed by the gray scale correction circuit 72 to output it to the display section 76. The display section 76 comprises, for example, an LCD (Liquid Crystal Display), and displays the image based on the image signal processed by the signal conversion section 62.
In the CCD imaging devices included in the imaging section 60, since signals generated by a large number of photodiodes, which are arranged two-dimensionally in the form of a matrix, are serially output on a pixel-by-pixel basis, the signal conversion section 62 has been obliged to process the signals serially. Since the refresh rate of the display section 76 is generally 60 Hz, the signal conversion section 62 had to process all signals of the pixels of one field, which are output from the CCD imaging devices, within a period of 1/60 seconds.
Although power consumption can be reduced by lowering a clock frequency in performing a digital signal processing, in the case of the image display apparatus, there is a certain limitation in reducing the clock frequency because the refresh rate of the display section 76 is generally not changeable, and it is difficult for the image display apparatus to be designed in reduced power consumption.
Furthermore, since a quantity of signals to be processed in the signal conversion section 62 becomes larger with an increase in number of the pixels of the CCD imaging devices, a high speed processing is required for the image display apparatus in order to process these signals within a certain period ( 1/60 seconds), and the clock frequency becomes higher, resulting in more increase in power consumption.