TECHNICAL FIELD

The present technology relates to an image processing device, a display device, and an image processing method, and more particularly relates to processing an image signal for a display panel in which a display image is generated by light passing through a rear liquid crystal cell and a front liquid crystal cell.

BACKGROUND ART

Various structures are known as liquid crystal display devices. Patent Document 1 below discloses a dual liquid crystal cell type liquid crystal display device as one of the structures.

CITATION LIST

Patent Document

Patent Document 1: WO 2016/063675 Pamphlet

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In a dual liquid crystal cell type display device, a problem occurs that display images of two liquid crystals appear doubled due to parallax when observed from an angle.

Therefore, for example, a signal input to a rear liquid crystal cell is subjected to gamma conversion into a gamma value of one or less, to thereby saturate the rear liquid crystal cell to 100% transmittance at a certain gradation or higher, or a filter process for expanding in a plane direction is performed on the signal input to the rear liquid crystal cell, so as to reduce the image shift due to parallax.

However, for example, when a signal of a small area like a white spot is displayed on a black background, although the white spot displayed on the rear liquid crystal cell spreads due to the filter process described above, an image displayed on the rear liquid crystal cell may be seen through due to leaked light from a front liquid crystal cell, and surroundings of the white spot may appear to shine lightly, resulting in reduced image quality.

Further, when the spread white spot on the rear liquid crystal cell side becomes brighter by the gamma conversion process, the leaked light increases and the image quality further deteriorates.

Accordingly, it is an object of the present technology to reduce these image quality deteriorations in a case where a dual liquid crystal cell type display device is used.

Solutions to Problems

An image processing device according to an embodiment of the present technology includes a gradation value conversion unit that performs a gradation value conversion on an input image signal, which is an image signal for a display panel in which a display image is generated by light passing through a rear liquid crystal cell and a front liquid crystal cell, so as to generate a rear image signal for the rear liquid crystal cell, and a limit processing unit that performs a process of limiting a value of the rear image signal output from the gradation value conversion unit to a limit value.

The image signal to be processed by the image processing device is an image signal used in a dual liquid crystal cell type liquid crystal display panel. The image processing device processes an image signal for each of a front liquid crystal cell and a rear liquid crystal cell of a dual liquid crystal cell type liquid crystal display panel. In this case, the limit process is performed on the rear image signal generated by the gradation value conversion.

In the image processing device according to the present technology described above, it is conceivable to include a maximum value detection unit that detects a maximum value of the input image signal, in which the limit processing unit sets the limit value to a value based on the maximum value detected by the maximum value detection unit.

That is, the maximum value of the input image signal is detected, and a value that changes as a value based on the maximum value is used as the limit value.

In the image processing device according to the present technology described above, it is conceivable that the limit processing unit sets the maximum value detected by the maximum value detection unit as the limit value.

That is, the maximum value of the input signal is directly used as the limit value.

In the image processing device according to the present technology described above, it is conceivable that the maximum value detection unit detects the maximum value for every area of a plurality of areas set in the image, and the limit processing unit performs, for every area, a limit process with a limit value based on a maximum value in the area.

That is, the image area of one frame is divided and set into a plurality of areas. Then, the maximum value of the input signal is detected for every area, and the limit process of the rear image signal is performed, for every area, with the limit value based on the maximum value.

In the image processing device according to the present technology described above, it is conceivable to include a lower limit processing unit that outputs, if the maximum value detected by the maximum value detection unit is less than a lower limit value that is set, the lower limit value as the maximum value.

That is, if the detected maximum value is larger than or equal to the set lower limit value, the detected maximum value is output as it is, but if the detected maximum value is less than the lower limit value, the detected maximum value is output instead of the lower limit value.

In the image processing device according to the present technology described above, it is conceivable to include a time filter unit that suppresses a variation amount in a time axis direction of the maximum value detected by the maximum value detection unit.

For example, the variation amount is suppressed so that the maximum value of the current frame of the input image signal and the maximum value of the previous frame (in a case of dividing into areas, the maximum value of a certain area of the current frame and the maximum value of the corresponding area of all frames) do not change rapidly.

In the image processing device according to the present technology described above, it is conceivable to include a scene change detection unit that detects a scene change for the input image signal, in which the time filter unit changes a filter operation if a scene change is detected.

For example, the scene change detection unit detects whether or not a scene as an image content has changed by comparing the current frame and the previous frame. The time filter unit switches the filter characteristic or switches on and off of the filter process in response to detection of a scene change.

In the image processing device according to the present technology described above, it is conceivable that a lower limit processing unit that sets, if the maximum value detected by the maximum value detection unit is less than a lower limit value that is set, the maximum value as the lower limit value, and a moving image detection unit that detects whether or not the input image signal is a moving image, in which the lower limit processing unit sets the lower limit value to a different value between when the input image signal is a moving image and when the input image signal is not a moving image.

For example, the lower limit value in the lower limit process is set to be different between when the input image signal is a moving image and when the input image signal is a still image.

In the image processing device according to the present technology described above, it is conceivable to include a spatial filter unit that suppresses a variation amount in a spatial direction of the maximum value in every area of a plurality of areas set in an image.

That is, with respect to the maximum value in each area, the filter process is performed so as not to cause a rapid change in a spatial direction (image plane direction in which a plurality of areas is adjacent to each other).

In the image processing device according to the present technology described above, it is conceivable that the gradation value conversion unit performs gamma conversion with a gamma value smaller than one.

The gamma conversion with a gamma value smaller than one is performed in order to perform good gradation expression in a state that the front image and the rear image are combined. In this case, a limit process is performed.

In the image processing device according to the present technology described above, it is conceivable to include a spatial processing unit that performs on the rear image signal a spatial filter process to make a transmission pixel range of an image in the rear liquid crystal cell larger than that of an image in the front liquid crystal cell.

That is, the spatial filter process is performed so as to blur the rear image. Specifically, a process like a low-pass filter for the rear image signal is performed so that the range of transmitting pixels on the rear liquid crystal cell side is enlarged to blur the image with respect to the image of the front liquid crystal cell by the front image signal.

In the image processing device according to the present technology described above, it is conceivable to include a front image generation unit that performs a calculation process using the rear image signal on the input image signal to generate a front image signal for the front liquid crystal cell, in which the input image signal is a color image signal, the gradation value conversion unit performs gradation value conversion on a monochrome image signal converted from the color image signal, and the front image generation unit generates the front image signal by dividing the input image signal that is a color image signal by the rear image signal processed by the limit processing unit.

That is, each of gradation values of, for example, R, G, and B as an image signal that is a color image signal is divided by the gradation value of the rear image signal after the limit process, so as to obtain the gradation values of R, G, and B as the front image signal.

A display device according to an embodiment of the present technology includes a display panel in which a display image is generated by light passing through a rear liquid crystal cell and a front liquid crystal cell, a gradation value conversion unit that performs a gradation value conversion on an input image signal, which is an image signal for the display panel, so as to generate a rear image signal for the rear liquid crystal cell, a limit processing unit that performs a process of limiting the value of the rear image signal output from the gradation value conversion unit to a predetermined limit value, and a front image generation unit that performs a calculation process using the rear image signal on the input image signal to generate a front image signal for the front liquid crystal cell.

In this display device, the display panel includes, for example, a light source unit, a rear liquid crystal cell, a diffusion layer, and a front liquid crystal cell, which are arranged in this order to form what is called a dual liquid crystal cell type liquid crystal display panel. A limit process is performed on the rear image signal for such a dual liquid crystal cell type liquid crystal display panel.

An image processing method according to the present technology is to perform a gradation value conversion and a process of limiting to a limit value in the image processing device described above.

Effects of the Invention

According to the present technology, in a dual liquid crystal cell type display device, light leakage generated around an isolated white spot is reduced by lowering a signal level of a rear liquid crystal cell, and by the reduction in the light leakage, a double image seen from an angle is improved, thereby obtaining an image quality improving effect.

Note that the effects described here are not necessarily limited, and may be any effect described in the present disclosure.

