Matsushita Electric Industrial Co., Ltd.

Keiichi Ito

Atsuhisa Kageyama

Katsuya Ishikawa

Hidetoshi Suzuki

Hisao Kunitani

Yuki Kakuya

Nobutaka Okada

The present invention provides a gradation correction device which can perform gradation correction using digital feedback processing, and furthermore, can control the digital feedback processing with high accuracy. The gradation correction device is provided with a correction gain adjustable amount generation circuit () and a correction gain generation circuit (), and the correction gain adjustable amount generation circuit () obtains a correction gain adjustable amount which is non-linear in relation to a difference S between a reference luminance level Yband a maximum luminance level, and greater gamma correction is carried out as the value of the difference is larger.

Gradation correction apparatus

A luminance signal processing apparatus that detects an average luminance level, adaptively to various video signal formats. This luminance signal processing apparatus includes a window pulse generation unitfor generating a window pulse signal Sthat indicates a period during which a luminance signal of an input video signal is sampled; a luminance value addition unitfor obtaining a total sum of luminance values of the luminance signal in the period indicated by the window pulse signal S; a number-of-pixel addition unitfor obtaining the number of pixels in the period indicated by the window pulse signal S; a bit shift unitfor bit-shifting an output signal of the luminance value addition unitand an output signal of the number-of-pixel addition unit, respectively; and a division unitfor dividing the bit-shifted output signal of the luminance value addition unitby the bit-shifted output signal of the number-of-pixel addition unit, thereby obtaining an average luminance level.

Apparatus for processing luminance signal

An object of the present invention is to provide a signal processor which improves the offset accuracy of a video signal without increasing the number of bits of a circuit. An N-bit adder () adds a video signal (S) and an upper-N-bit signal of a brightness control signal (S) as an offset value. A 1-bit pulse generator () generates a 1-bit pulse signal (S) in which '1' and '0' have equal chances of appearing at random. A selector () selects the 1-bit pulse signal (S) when the LSB of the brightness control signal (S) is &#x201c;1&#x201d;, while selects a ground level &#x201c;0&#x201d; when the LSB is &#x201c;0&#x201d;, and supplies the selected signal to a carry input of the N-bit adder ().

Signal processor

A gradation correction circuit comprises: an arithmetic means ( ) for operating an output value corresponding to each broken point of a broken line in a vertical blanking period; a level detection circuit for identifying a size relation between each broken line point which is an input value corresponding to each broken point and an input video signal, and calculating a difference between the input video signal and each broken line point; and a correction means ( ) for selecting a gradient of the broken line on the basis of the result identified by the level detection circuit , and performing gradation correction of the input video signal on the basis of the selected gradient of the broken line, the output value calculated by the arithmetic means, and the difference calculated by the level detection circuit, wherein the arithmetic means and the correction means share a number of circuits ( ). Therefore, there is provided a gradation correction circuit where video correction with high precision can be realized without using a memory storing a lookup table, or without increasing a circuit scale.

Gradation correction circuit, and &ggr; correction apparatus

An appropriate correction quantity is obtained for a video luminance signal on an individual video basis with a characteristic value, like the maximum or average value, of the luminance signal taken into account, thereby performing gray scale correction more effectively. A dynamic gamma correction apparatus for performing a correction on a video luminance signal includes: a correction start point control section for obtaining a correction start point, which is a lower limit of a given correction range, in accordance with a characteristic value of the luminance signal; a gamma correction quantity calculating section for obtaining a provisional correction quantity for the luminance signal to be corrected using the correction start point and the luminance signal; a gamma correction gain control section for obtaining a gain for the provisional correction quantity in accordance with the characteristic value of the luminance signal; a multiplier for obtaining a product of the provisional correction quantity and the gain as a gamma correction quantity; and an adder for obtaining a sum of the luminance signal and the gamma correction quantity and outputting the sum. The correction start point and the gain for the provisional correction quantity are controllable in accordance with the characteristic value of the luminance signal. Thus, an appropriate gamma correction quantity can be obtained as a final correction quantity.

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Osaka, Japan

Keiichi Ito