Display device having backlight

• US 9,123,284 B2
• Filed: 09/05/2012
• Issued: 09/01/2015
• Est. Priority Date: 05/23/2008
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yoshida, Yasunori
• Primary Examiner(s): Sitta, Grant
• Assistant Examiner(s): HERMANN, KIRK W
• Application Number:
  US13/603,496
• Publication Number:
  US 20120327141A1
• Time in Patent Office: 1,091 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G09G 2300/0443 with several sub-pixels for the same colour in a pixel, not specifically used to display gradations G09G3/364 takes precedence
• CPC Class Codes: G09G 2300/0491 Use of a bi-refringent liquid crystal, optically controlled bi-refringence [OCB] with bend and splay states, or electrically controlled bi-refringence [ECB] for controlling the color
• CPC Class Codes: G09G 2310/0232 Special driving of display border areas
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/10 Special adaptations of display systems for operation with variable images
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A display device in which the image quality is improved by control of the peak luminance. A plurality of instantaneous luminances are expressed by performing signal writing to each pixel plural times within one frame period. The gray level is expressed by controlling time integration levels of the plurality of instantaneous luminances. Moreover, the time integration level is increased as the level of gray level data of the pixel is higher, and the time integration level is increased as the average value of gray level data of an image to be displayed is smaller.

Claims

1. A display device comprising a plurality of pixels,

a backlight for emitting light to the plurality of pixels,

wherein in each pixel, a plurality of subframe periods are provided in one frame period, and a gray level of the plurality of pixels is expressed in accordance with a time integration level of instantaneous luminances expressed in the plurality of subframe periods,

wherein when an average value of gray level data of an original image is larger than a predetermined value, a first black display is performed in the plurality of pixels in one of the plurality of subframe periods,

wherein when the average value of the gray level data of the original image is smaller than the predetermined value, a second black display is performed in the plurality of pixels in the one of the plurality of subframe periods,

wherein the second black display includes a black portion and a brightness portion,

wherein a luminance of the backlight is constant in the plurality of subframe periods, and

wherein each of the plurality of pixels comprises a semiconductor layer comprising an oxide semiconductor.

2. The display device according to claim 1, wherein the plurality of subframe periods are equal in length.

3. The display device according to claim 1, wherein the time integration level is increased with respect to the gray level data by power law.

4. The display device according to claim 1, wherein the average value of the gray level data of the original image is obtained by averaging gray levels of some of pixels among the plurality of pixels.

5. The display device according to claim 1, wherein the display device is a liquid crystal display device.

6. The display device according to claim 1, wherein the display device is incorporated into one electronic device selected from the group consisting of a mobile computer, a portable image reproducing device, a goggle-type display, a portable game machine, a projector, a television receiver, a portable television receiver, a camera, a computer, and a mobile phone.

7. A display device comprising a plurality of pixels,

a backlight for emitting light to the plurality of pixels,

wherein in each pixel, a first subframe period and a second subframe period are provided in one frame period, and a gray level of the plurality of pixels is expressed in accordance with a time integration level of a first instantaneous luminance expressed in the first subframe period and a second instantaneous luminance expressed in the second subframe period,

wherein when an average value of gray level data of an original image is larger than a predetermined value, a first black display is performed in the plurality of pixels in the second subframe period,

wherein when the average value of the gray level data of the original image is smaller than the predetermined value, a second black display is performed in the plurality of pixels in the second subframe period,

wherein the second black display includes a black portion and a brightness portion,

wherein a luminance of the backlight is constant in the first subframe period and the second subframe period, and

wherein each of the plurality of pixels comprises a semiconductor layer comprising an oxide semiconductor.

8. The display device according to claim 7, wherein the first subframe period and the second subframe period are equal in length.

9. The display device according to claim 7, wherein the display device is a liquid crystal display device.

10. The display device according to claim 7, wherein the display device is incorporated into one electronic device selected from the group consisting of a mobile computer, a portable image reproducing device, a goggle-type display, a portable game machine, a projector, a television receiver, a portable television receiver, a camera, a computer, and a mobile phone.

11. A display device comprising:

an image feature amount detection portion for detecting gray level data distribution of gray level data of an original image;

a scale factor determination portion for determining a scale factor in accordance with the gray level data distribution detected by the image feature amount detection portion;

a gray level data conversion portion for converting the gray level data of the original image into gray level data of a first subimage and gray level data of a second subimage in accordance with the scale factor determined by the scale factor determination portion; and

a display portion for displaying the first subimage and the second subimage,

a backlight for emitting light to the display portion,

wherein when an average value of the gray level data of the original image is larger than a predetermined value, the second subimage is a black display,

wherein when the average value of the gray level data of the original image is smaller than the predetermined value, the second subimage includes a black portion and a brightness portion, and

wherein a luminance of the backlight of the first subimage and a luminance of the backlight of the second subimage are the same.

12. The display device according to claim 11, further comprising a display control portion that converts the gray level data converted by the gray level data conversion portion into a signal for display, and generates a display control signal for controlling the display portion.

13. The display device according to claim 11, wherein the image feature amount detection portion comprising:

a gray level data distribution generation portion for reading and classifying the gray level data of the original image and generating the gray level data distribution;

a memory for storing the gray level data distribution generated by the gray level data distribution generation portion; and

an image feature amount calculation portion having a function of reading the gray level data distribution stored in the memory and calculating the image feature amount, and a function of resetting the memory.

14. The display device according to claim 11, wherein the image feature amount detection portion comprising:

a first memory for reading a plurality of data of the original image;

a text region detection portion for detecting a text region in the display portion from the plurality of data stored in the first memory, and writing information on the detected text region to a second memory;

a gray level data distribution generation portion for reading and classifying the gray level data stored in the first memory and generating the gray level data distribution;

the second memory for storing the gray level data distribution generated by the gray level data distribution generation portion; and

an image feature amount calculation portion having a function of reading the gray level data distribution stored in the second memory and calculating the image feature amount, and a function of resetting the second memory.

15. The display device according to claim 11, wherein the display device is a liquid crystal display device.

16. The display device according to claim 11, wherein the display device is incorporated into one electronic device selected from the group consisting of a mobile computer, a portable image reproducing device, a goggle-type display, a portable game machine, a projector, a television receiver, a portable television receiver, a camera, a computer, and a mobile phone.