JP2010224355A - Electro-optical device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve visibility in accordance with an image to be displayed when surrounding brightness is very bright. <P>SOLUTION: The device has an optical sensor 210 detecting surrounding brightness, a discriminating circuit 25 discriminating whether detected surrounding brightness exceeds a threshold or not, an analyzing circuit 22 analyzing image data and outputting a statistical value of brightness components of the image, an image processing circuit 23 in which brightness components in the image data is used as an input value and converting the input value to an output value, and a display panel 100 displaying the image based on the output value. When surrounding brightness exceeds the threshold, the image processing circuit 23 reduces the input value if the input value is less than the statistical value, or increases the input value if the input value exceeds the statistical value, thereby converting it to an output value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for performing image processing based on a statistical value of image data and displaying the image data.

There has been proposed a technique for obtaining an image in consideration of the characteristics of the output device by performing image processing based on a statistical value of the image data when the input image data is output from the output device (Patent Literature). 1).
On the other hand, electronic devices such as mobile phones and PDAs (personal digital assistants) are used in various environments from bright places to dark places due to their portability. For this reason, a technique has been proposed in which the brightness of a display image is adjusted by detecting the ambient brightness with an optical sensor and controlling the brightness of the backlight in accordance with the detection result (see Patent Document 2). ).

Japanese Patent Laying-Open No. 2006-180311 (FIG. 8) JP 2006-29832 A (FIG. 1)

However, when the peripheral luminance is very high, there is a problem that the visibility of the displayed image is lowered.
The present invention has been made in view of such circumstances, and one of its purposes is to provide a technique that appropriately suppresses a reduction in the visibility of a display image even in such a case. .

In order to achieve the above object, an electro-optical device according to the present invention includes an optical sensor that detects peripheral luminance, a determination circuit that determines whether the peripheral luminance detected by the optical sensor exceeds a threshold value, and An analysis circuit that analyzes image data and outputs a statistical value of luminance information indicating the luminance of a pixel; and an image processing circuit that takes luminance information in the image data as an input value and converts the input value into an output value. When the ambient brightness exceeds the threshold, the input value is decreased for an input value lower than the statistical value, while the input value is increased for an input value higher than the statistical value, and the output An image processing circuit for converting the value into a value; and a display panel for displaying an image based on the output value. According to the present invention, when changing the luminance information of the pixel, the fixed point of the input / output characteristics is set to the statistical value of the luminance information, so that appropriate image processing is performed according to the image to be displayed. . For this reason, it becomes possible to improve the visibility of a display image.
Note that the statistical value of the luminance information refers to a value when the luminance information for a predetermined number of pixels is statistically processed, for example, an intermediate value or an average value described later.

In the present invention, it is preferable that the threshold value corresponds to a maximum luminance value that can be displayed on the display panel. This is because when the peripheral luminance exceeds the maximum value of luminance that can be displayed on the display panel, the reduction in visibility starts to be noticeable.
In the present invention, the image processing circuit converts the input value into the output value according to a predetermined input / output curve, and the input / output curve includes the minimum value of the input value and the statistical value. It is good also as a structure which has the 1st part which passes, and the 2nd part which passes the maximum value of the said input value, and the said statistical value.
Furthermore, in the present invention, the image processing circuit may set the input / output characteristics based on a difference between the peripheral luminance and the threshold when the peripheral luminance is equal to or less than the threshold. According to this configuration, it is possible to suppress a decrease in display quality when the peripheral luminance varies in the vicinity of the threshold value.
In addition to the electro-optical device, the present invention can be conceptualized as an electronic apparatus having the electro-optical device.

It is a figure which shows the structure of the mobile telephone to which the electro-optical apparatus which concerns on embodiment is applied. 2 is a block diagram illustrating a configuration of the electro-optical device. FIG. It is a figure which shows the statistical value etc. of image data. It is a figure which shows the image processing in the same electro-optical apparatus. It is a figure which shows the image processing which concerns on an application and modification (the 1). It is a figure which shows the image processing which concerns on an application and modification (the 2).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a mobile phone to which the electro-optical device according to the embodiment is applied.
As shown in this figure, the mobile phone 200 includes a plurality of operation buttons 202 and a cursor key 204, and a display panel 100 in an electro-optical device, as well as an earpiece 206 and a mouthpiece 208. In addition, a light receiving window of the optical sensor 210 is provided, for example, in the lower left corner of the display panel 100, and detects the peripheral luminance of the mobile phone.

FIG. 2 is a block diagram illustrating a configuration of the electro-optical device 10 according to the embodiment.
As shown in this figure, the electro-optical device 10 includes a luminance conversion circuit 21, an analysis circuit 22, an image processing circuit 23, an RGB conversion circuit 24, a determination circuit 25, a drive circuit 30, a display panel 100, and an optical sensor 210. .

The display panel 100 is, for example, an active matrix type liquid crystal panel. In the display area, a plurality of rows of scanning lines 112 extend in the horizontal direction in the drawing, and a plurality of columns of data lines 114 extend in the vertical direction in the drawing. The scanning lines 112 are provided so as to be electrically insulated from each other, and the pixels 110 are arranged corresponding to the intersections of the scanning lines 112 and the data lines 114, respectively. ing.
Each pixel 110 corresponds to one of R (red), G (green), and B (blue), and expresses one dot color with three pixels of RGB. For this reason, in this embodiment, when the number of scanning lines 112 in the display panel 100 is “m” and the number of columns of the data lines 114 is “3n”, which is a multiple of 3, dots are vertically aligned on the display panel 100. They are arranged in a matrix with m rows × n horizontal columns.
Although not shown, an illumination device (backlight) using a white LED or the like as a light source is provided, and light is directed from the back side (the back side of the paper) of the display panel 100 toward the observation side (the front side of the paper). Has been issued.

  In FIG. 2, the configuration other than the display in the mobile phone 200, for example, the configuration such as wireless communication is omitted. In the present embodiment, the image data is supplied from a main control circuit (not shown) that controls the operation of the mobile phone 200. This image data defines the RGB components of dots in the color image to be displayed on the display panel 100.

The luminance conversion circuit 21 converts the RGB component of the image data into a luminance component Y and color difference components Cb and Cr, respectively.
The analysis circuit 22 analyzes the luminance component Y converted by the luminance conversion circuit 21 for m · n dots corresponding to one frame of the image, and outputs the statistical value. In the present embodiment, an intermediate value (median value) is used as an example of a statistical value. Here, the intermediate value is the (m · n / 2) th from the top when the luminance components Y for m · n dots corresponding to one frame of the image are arranged in order from the smallest value. That is, a value located in the middle (center). For this reason, in this embodiment, the analysis circuit 22 first accumulates the luminance component Y for m · n dots corresponding to one frame of the image, and secondly, the accumulated luminance component Y from a small value. Third, the (m · n / 2) -th luminance component from the top of the array is output as an intermediate value.
For example, when a relatively dark image whose luminance component histogram is, for example, as shown in FIG. 3A is to be analyzed, the luminance component Y of this image is arranged in order from a smaller value by one frame. When the result is as shown in 3 (b), the intermediate value is the (m · n / 2) -th luminance component “0.25”. If an intermediate value is used as the statistical value, the analysis circuit 22 is substantially only required to perform the rearrangement process, and complicated statistical calculation is not required.

On the other hand, the determination circuit 25 determines whether or not the peripheral luminance detected by the optical sensor 210 exceeds the maximum luminance that can be displayed on the display panel 100. Here, the maximum luminance value that can be displayed on the display panel 100 is the luminance when white is displayed on the display panel 100 by setting all the transmittances of the RGB pixels 110 to the maximum value.
Therefore, the maximum value of luminance that can be displayed on the display panel 100 is determined by the transmittance of the RGB pixels 110 and the luminance of the light emitted to the display panel 100 by the lighting device. The determination circuit 25 is configured to store this maximum value as a threshold value and to compare it with the detected ambient luminance.

When the peripheral luminance detected by the optical sensor 210 exceeds the maximum luminance that can be displayed on the display panel 100, the image processing circuit 23 displays the luminance component Y converted by the luminance conversion circuit 21 in FIG. It is changed according to the input / output characteristics (tone curve) as shown and output as the luminance component Y ′. This input / output characteristic is a linear characteristic with a slope of “1” passing through the origin, that is, a characteristic in which an input value is output as it is, a point B corresponding to a minimum value, a point W corresponding to a maximum value, and a point C corresponding to a statistical value are fixed points. The arc-shaped curve (first portion) that passes through points B and C and swells downward in the shadow region below point C, and highlights that pass through points C and W and exceed point C In the region, an arcuate curve (second portion) bulging upward is connected by a point C.
The input / output characteristics in FIG. 4 are curves with the point C as a fixed point when the statistical value is “0.25”, but the statistical values are “0.5” and “0.75”. If there is a curve, points C ′ and C ″ are fixed points as indicated by broken lines in FIG.
Further, in this embodiment, the image processing circuit 23 uses the luminance component Y converted by the luminance conversion circuit 21 when the peripheral luminance detected by the optical sensor 210 is equal to or lower than the maximum luminance that can be displayed on the display panel 100. Is output as it is as the luminance component Y ′.

The RGB conversion circuit 24 reconverts the luminance component Y ′ changed by the image processing circuit 23 and the color difference components Cb and Cr converted by the luminance conversion circuit 21 into RGB components.
The drive circuit 30 converts the RGB component image data into a data signal and writes it into the corresponding pixel 110. Specifically, one line of RGB component image data is accumulated, the scanning line 112 of the one line is selected, and a data signal is supplied to the data line 114. As is well known, when the scanning line 112 is selected, a voltage corresponding to the data line 114 is written in the pixel 110 in the case where the display panel 100 is a transmissive liquid crystal panel, and transmission corresponding to the voltage is performed. Become a rate.
Therefore, by performing this operation in the order of the first, second, third,..., Mth rows, the display panel 100 displays an image corresponding to the RGB components reconverted by the RGB conversion circuit.

  According to this embodiment, when the peripheral luminance detected by the optical sensor 210 exceeds the maximum luminance that can be displayed on the display panel 100, the contrast enhancement processing is performed on the image data supplied from the main control circuit. Displayed on the display panel 100. Furthermore, in this embodiment, when changing the luminance component in the contrast enhancement process, the fixed point of the tone curve is set as the statistical value of the image data. For this reason, it is possible to improve visibility because it is displayed with appropriate contrast enhancement processing according to dark images where small luminance components are concentrated and bright images where large luminance components are concentrated. Become.

<Application and modification>
The present invention is not limited to the above-described embodiments, and various applications and modifications are possible as follows.

<Part 1>
When the peripheral luminance detected by the optical sensor 210 is less than or equal to the maximum value of luminance that can be displayed on the display panel 100, the visibility of the display image does not decrease much compared to when the maximum value is exceeded. There is little need to emphasize. For this reason, in the embodiment, the image processing circuit 23 is configured not to perform contrast enhancement processing.
However, when the peripheral luminance fluctuates near the maximum luminance value that can be displayed on the display panel 100, the contrast enhancement processing is turned on and off, and the display quality may be deteriorated.
Therefore, when the peripheral brightness is equal to or lower than the maximum displayable brightness, the tone curve is gradually changed according to the difference between the peripheral brightness and the maximum displayable brightness as shown in FIG. You may let them.
FIG. 5 shows an example in which the statistical value is “0.5”.

<Part 2>
As shown in FIG. 6, in addition to the fixed points of point B, point C, and point W, the tone curve includes a spline curve and a Bezier curve that pass through the control point Sd in the shadow area and the control point Hg in the highlight area. It may be obtained by a mathematical curve such as

<Part 3>
When calculating the statistical value of image data, not all m · n dots are used, but the number of dots appropriately thinned out may be analyzed. If the number of target dots is reduced in this way, the burden on the analysis circuit 22 and the image processing circuit 23 can be reduced. On the contrary, if there is movement in the image, the number of dots for several frames may be analyzed. In any case, when the statistical value of the image data is obtained, a predetermined number of dots may be set as the analysis target.

  In addition to the above-described intermediate value, an average value that is a value obtained by averaging the luminance information over a predetermined number of dots may be used as the statistical value. When the average value is used as the statistical value, the analysis circuit 22 substantially needs to perform addition and division processing, and no complicated calculation is required.

  The RGB component is converted into the HIS component, that is, the hue, hue, intensity, and saturation. Among these, the intensity is used as luminance information, and the tone curve is converted into the intensity statistical value. A fixed point may be set. In addition, since the RGB component includes luminance information in part, the RGB component may be analyzed to obtain a statistical value, and a contrast enhancement process may be performed for each RGB component.

<Part 4>
The display panel 100 is not limited to a liquid crystal panel, and may be a self-luminous type such as an organic EL panel or a plasma display. Since such a self-luminous display panel is not provided with a backlight, the maximum displayable luminance value is determined only by the light emission characteristics of the display panel.
In addition, an electronic device to which the electro-optical device is applied is not limited to a mobile phone, and can be applied to various electronic devices. Examples of such electronic devices include digital still cameras, laptop computers, liquid crystal televisions, viewfinder type (or monitor direct view type) video recorders, car navigation devices, electronic notebooks, calculators, word processors, workstations, videophones, The thing which has display parts, such as equipment provided with a touch panel, is mentioned.

DESCRIPTION OF SYMBOLS 10 ... Electro-optical device, 22 ... Analysis circuit, 23 ... Image processing circuit, 25 ... Judgment circuit, 100 ... Display panel, 200 ... Cell-phone, 210 ... Optical sensor

Claims (5)

An optical sensor that detects ambient brightness;
A determination circuit for determining whether or not the ambient luminance detected by the light sensor exceeds a threshold;
An analysis circuit that analyzes image data and outputs a statistical value of luminance information indicating the luminance of the pixel;
An image processing circuit that takes luminance information in the image data as an input value and converts the input value into an output value, and when the peripheral luminance exceeds the threshold, An image processing circuit that reduces an input value while increasing the input value for an input value that exceeds the statistical value and converts the input value to the output value;
A display panel for displaying an image based on the output value;
An electro-optical device comprising: The electro-optical device according to claim 1, wherein the threshold value corresponds to a maximum luminance value that can be displayed on the display panel. The image processing circuit converts the input value into the output value according to a predetermined input / output curve,
The input / output curve is
A first portion that passes through a minimum value of the input value and the statistical value;
A second portion that passes through the maximum value of the input value and the statistical value;
The electro-optical device according to claim 1, wherein the electro-optical device is provided. The image processing circuit includes:
When the peripheral luminance is less than or equal to the threshold value,
The electro-optical device according to claim 1, wherein the input / output characteristics are set based on a difference between the peripheral luminance and the threshold value.   An electronic apparatus comprising the electro-optical device according to claim 1.

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