R & D

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The 4K/8K satellite broadcasting that began in December 2018 is characterized not only by high-definition images but also by a wide range of colors that can be reproduced (color gamut). Display devices that are capable of reproducing a wide color gamut require the emission of light that has high color purity for more vivid colors. Quantum dots have been attracting attention in recent years for use in new lumines-cent materials that feature high color purity. At STRL, we have been working on quantum dot light-emitting diodes for thin, lightweight displays that are capable of reproduc-ing a wide color gamut.

Quantum dot materialsQuantum dots are semiconductor particles that are gener-

ally several nanometers* in size (Fig. 1). The energy states that the electrons in the semiconductor can take vary with the particle size, and the emission wavelength (and thus the color) depends on the energy states. Smaller particles result in shorter emission wavelengths (colors closer to blue) and larger particles result in longer wavelengths (colors closer to red). It is thus possible to adjust the emission color over a wide range by controlling the particle size (Fig. 2). How-ever, most quantum dot materials that have been reported so far contain the toxic element cadmium. STRL has been searching for quantum dot materials that do not contain cadmium.

Quantum dot light-emitting diodesA surface-light-emitting device can be fabricated by

sandwiching a thin film that is populated with quantum dots between electrodes (Fig. 3). However, if the light-emitting layer contains quantum dots of different sizes, it is not possible to obtain the desired color. To obtain high color purity, it is therefore important that the quantum dots that constitute a pixel (red, green, or blue) are of the same size. So far, the emission of red light has been achieved in the trial production of devices using quantum dot ma-terials that do not contain cadmium (Fig. 4). Fabricating such light-emitting devices on a flexible substrate material such as plastic would also make their application to thin, lightweight display devices possible.

In future work, we will continue to develop new materi-als and improve the device structure to further improve light emission efficiency and achieve higher color purity.

*A nanometer is one-millionth of a millimeter.

Genichi Motomura

Quantum Dot Light-emitting Diode for Displays with Vivid Color

Emission color

Quantum dot size

Figure 2: Light emission from quantum dots of various sizes (under irradiation with ultraviolet light)

Semiconductor particle

Several nanometers

Figure 1: Typical quantum dot shape

Metal Cathode

Electron injection layerElectron transport layerQuantum dot light-emitting layer

Hole transport layer

Hole injection layer

Substrate

Transparent anode

Light emission

ー

＋

Figure 3: Structure of a quantum dot light-emitting diode

Light Emission

Transparentanode

Metal cathode

Figure 4: Emission of red light with prototype

R & D

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Development of More Efficient Video Coding Technology

The 4K/8K satellite broadcasting service began in De-cember 2018, making it possible to view 4K/8K Super Hi-Vision (SHV) programs in the home. The delivery of such ultrahigh-definition video by broadcasting requires video coding technology that is capable of efficiently compressing huge amounts of data. For achieving terrestrial broadcast-ing of SHV, the video signal must be transmitted via a more limited transmission capacity. STRL has been researching on technologies for more efficient video compression to realize future broadcasting services. A technology that is currently being researched is described here.

Generally, video compression methods involve partition-ing an image into multiple blocks, predicting the trajectory of the moving object within each block, and transmitting the prediction residue to reduce the amount of information (Fig. 1). The regions in which there is little movement over a wide range are partitioned into large blocks and the regions in which there are fine movements are partitioned into small blocks. The motion information calculated for

each block is transmitted. However, the amount of motion information to be transmitted increases with the number of blocks into which the image is partitioned.

To address this problem, we developed a method that reduces the amount of information to be transmitted by obtaining motion information within the target block on the receiving side. Motion information for partial regions within target blocks is interpolated on the receiving side by using the motion information of adjacent blocks (Fig. 2). Doing so eliminates the need to transmit the motion infor-mation obtained by fine subdivisions, as is conventionally done, thus reducing the amount of information transmitted.

In future work, we will continue with R&D on video coding technology for future broadcasting services.

Shunsuke Iwamura

Transmit the least amount of blocks information for regions in which there is little movement (e.g. background, etc).

Predict movement and transmit the prediction residue for regions in which there is fine movement

Video flow

Motion information to be transmitted

(A) Conventional method (B) Proposed method

Interpolated on the receiving side by motion information obtained from surrounding blocks

Block

Region with a large number of subdivisions

Target block

Region with a large number of subdivisions

Figure 1: Image compression Figure 2: Reduction in the amount of motion information to be transmitted

R & D

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Sign language summaries of competition information and results increase the enjoyment of sports programs and sports news for persons with impaired hearing, and STRL is moving forward with research on presenting sports com-petition information as computer-generated sign language. Here, we describe a translation assistant system for the ef-ficient production of sign language CG (computer graphic) from Japanese text. Motion capture is used to prepare sign language finger motion and facial expression data. Japanese text that is input to the system is automatically translated to sign language word strings by machine translation. How-ever, the context cannot be completely analyzed for some input sentences, so the order in which the sign language is presented may be incorrect. To address this problem, we developed a user interface that facilitates the rearrangement and insertion of sign language words.

In the example presented in the figure, a nod action that represents a semantic separator is inserted in the wrong

place. The interface we developed displays the word string and makes it possible to change the order or insert sign language words intuitively by a mouse operation to make corrections while checking the generated sign language CG. There is also a function that records corrections for use as training data and a function for later reuse of the correc-tion history as templates. These functions can be used to improve the translation accuracy.

The system requires that some work be performed by persons who understand sign language, but the amount of training data increases with the continued use of the system so production efficiency should increase over time. In fu-ture work, we will conduct trials on sports news programs and extend the application of computer-generated sign language to general news programs.

Shuichi Umeda

Translation Assistant System for Sign Language CG from Japanese Text for Sports News

Computer-generated sign language

AI support

Training data

Machine translation Motion synthesis

・Correction of word string・Correction of computer graphic movement

Recording of corrections

‘Tokyo’ , ‘location’ , ‘nod’ , ‘Olympic’ , ‘nod’ , ‘be held’ , ‘nod’

Japanese text: “The Olympics are held in Tokyo”

Sign language word string:

Sign language word string

User interface for the production support system

Tokyo location nod Olympic nod be held nod

nodRearrangement of machine translation results

Sign language generation process in the translation assistant system