Imaging apparatus in which exposure control is performed to suppress changes in sensitivity due to changes in gradation mode

Abstract

A digital camera that can change gradation properties is provided which includes a CCD image pickup element for photographing a subject, an exposure control mechanism for controlling an exposure on the image pickup element, a digital processing circuit including a gradation converting circuit for generating image signals having different gradation properties (gamma properties) based on the output signal from the image pickup element, and a system controller including a selecting circuit for selecting one of the different gradation properties, which is used in the gradation converting circuit. In the digital camera, to suppress change of sensitivity (output level) due to a change of the gradation property, the exposure control mechanism changes a control target value to control the exposure in accordance with the selected gamma value so that the output level is maintained at a constant in the average exposure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a Divisional application of U.S. application Ser. No. 09 / 883,833, filed Jun. 18, 2001, which is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-183310, filed Jun. 19, 2000, No. 2000-188030, filed Jun. 22, 2000, and No. 2000-188031, filed Jun. 22, 2000, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an imaging apparatus in which a gradation (gamma: γ) property (gradation property curve) can be changed, and particularly to an imaging apparatus in which the gradation property can be changed and exposure control is improved. [0004] Moreover, the present invention relates to an imaging apparatus in which an image pickup device such as CCD is incorporated, and particularly to an imaging apparatus in which sensitivity is enhanced by addition of pixe...

AI Technical Summary

Benefits of technology

The present invention provides an imaging apparatus and method that can hold sensitivity and output image quality constant even when the gradation property changes. This is achieved by designating between two gradation modes and converting the original image signal to the output image signal in accordance with the designated mode. Additionally, the invention allows for enhanced sensitivity without deteriorating the quality of the output image. The invention also provides an imaging method that maintains a constant level of the output image signal even when the gradation property changes.

Problems solved by technology

Therefore, a problem is that the obtained output level changes.

Since the gradation property is changed, it is originally impossible to obtain an equal output level over a whole luminance distribution of the photographic subject.

Additionally, in the conventional digital camera, since these are not considered, the output level disadvantageously changes largely as described above.

Additionally, when this technique is actually applied to the electronic camera, the sensitivity can be enhanced, but a noise increases with the sensitivity enhancement.

Beyond simple resolution deterioration because of a decrease of the number of pixels, image quality deterioration further occurs.

However, this cannot be said to be correct in consideration about the noise.

Therefore, during imaging while the image quality, that is, the noise level is kept, the imaging with double sensitivity, that is, ½ of the standard exposure amount is a limitation.

In an analog adding system in the digital camera, there is a problem of saturation in an A / D converter.

However, in a usual non-addition time, the maximum value of CCD output signal is Dmax / 2, and a larger digital bit is wasted.

In other words, a relative quantized error disadvantageously becomes double from an ideal state.

In other words, the A / D converter with a larger number of bits than an originally necessary number of bits is necessary, and cost increase is unfavorably caused.

There is a problem that the image quality is deteriorated.

Images