Experimental observation of temperature-dependent characteristics for ...

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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 34, NO. 2, APRIL 2006

Experimental Observation of TemperatureDependent Characteristics for Temporal Dark Boundary Image Sticking in 42-in AC-PDP Jin-Won Han, Heung-Sik Tae, Senior Member, IEEE, Bhum Jae Shin, Sung-Il Chien, Member, IEEE, and Dong Ho Lee

Abstract—The temperature-dependent characteristics of temporal image sticking, especially temporal dark boundary image sticking, are investigated by observing the infrared (IR) emission characteristics relative to the panel-temperature rise during the reset period in a 42-in plasma television. A panel-temperature rise is induced in adjacent cells by the discharge cells (i.e., image-sticking cells) due to the iterant strong sustain discharge, thereby lowering the firing voltage for both the adjacent and discharge cells during the ramp-up period. However, the phosphor layers in the discharge cells are deteriorated due to the strong discharge, whereas the phosphor layers in the adjacent cells are not degraded due to the absence of the strong sustain discharge. Consequently, when the displayed image is white, the temporal boundary image-sticking cells exhibit a higher luminance with a dark background image. Meanwhile, when a single color image is displayed, the temporal boundary image-sticking cells induce a color difference with a dark background image. Index Terms—Boundary image sticking, panel-temperature rise, temporal image sticking.

I. INTRODUCTION

I

MAGE-STICKING is a critical issue that needs an urgent solution for the realization of a high image quality in plasma televisions [1]. Image sticking is known to be caused by the iterant strong sustain discharge during a sustain period over a few minutes, which means a residual or ghost image remains in a subsequent image when the previous image was continuously displayed over a few minutes [2]. Although the image-sticking phenomenon in discharge cells is essentially related to changes in the MgO surface or phosphor layer during a strong sustain discharge, the detailed mechanism of the image sticking problem is still not understood [2]–[8]. In particular, the cause for the image-sticking phenomenon occurring in cells adjacent to the discharge cells, referred to as temporal boundary image sticking, is not clear, since this is a nondischarge region [9]. Nonetheless, temporal dark boundary image sticking is known to be related to the reset discharge that is predominantly

Manuscript received May 1, 2005; revised November 13, 2005. This work was supported in part by the Korea Institute of Industrial Technology Evaluation and Planning under Grant R12-2002-055-02002-0 and in part by Brain Korea 21. J.-W. Han, H.-S. Tae, S.-I, Chien, and D. H. Lee are with the School of Electrical Engineering and Computer Science, Kyungpook National University, Daegu 702-701, Korea (e-mail: [email protected]). B. J. Shin is with the Department of Electronics Engineering, Sejong University, Seoul 143-747, Korea. Digital Object Identifier 10.1109/TPS.2006.872444

affected by the panel-temperature rise [10], [11]. Accordingly, this paper focuses on examining the relation between the panel-temperature rise and the temporal image-sticking phenomenon, especially temporal dark boundary image sticking. Moreover, the temperature-dependent characteristics of temporal dark boundary image sticking are extensively investigated by observing the infrared (IR) emission characteristics relative to the panel-temperature rise during the reset period in a 42-in plasma television (TV). II. EXPERIMENTAL SETUP Fig. 1(a) shows the commercial 42-in-wide video graphics array (WVGA) plasma-TV with asymmetric stripe barrier ribs and an optical measurement system employed in the current study. The test patterns used for the image sticking were made by a pattern generator, then transferred into the plasma display panel (PDP) module by image processing. A color analyzer (CA-100) and highly sensitive light detector (Hamamatsu, C6386) were used to measure the luminance and IR (828 nm) waveform, respectively, while a spectrum analyzer (PR 704) was used to measure the spectra of visible light (380–780 nm). As such, the visible spectra were measured in about two pixels of the adjacent cells and discharge cells when using a dark background after displaying the specific image patterns for over 15 min. The temperature on the front panel of the PDP module was measured using a pyrometer. In addition, an external heater was also used to heat the panel in a discharge-off state to investigate the thermal effect without the discharge effect. Fig. 1(b) shows the driving waveforms for the reset, address, and sustain periods employed in the current study. When displaying a dark background image, no address pulse was applied to the address (A) electrode during an address period, as shown in Fig. 1(b). Therefore, the dark background image was determined by the reset waveform, where the ramp-up time was 120 s and rampramp-down time was 200 s. The scan and address pulses were simultaneously applied to the scan (Y) and address (A) electrodes during an address period only when the bright images were displayed. The amplitude and width of the address pulse were 72 V and 1.2 s, respectively. The frequency for the sustain period was 200 kHz, and the sustain voltage was 176 V. The initialization is very important when observing the image sticking phenomenon, especially the temporal image sticking phenomenon. Thus, to exclude any effects of image sticking on subsequent experiments, the ensuing experiments were only per-

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HAN et al.: EXPERIMENTAL OBSERVATION OF TEMPERATURE- DEPENDENT CHARACTERISTICS

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Fig. 1. (a) Optical measurement system employed in current study and (b) driving waveforms for reset, address, and sustain periods when displaying bright and dark images.

formed after the panel temperature had been returned to room temperature based on continuing the turnoff state of the cells for an adequate amount of time after displaying the specific image patterns. III. EXPERIMENTAL OBSERVATION OF TEMPORAL DARK BOUNDARY IMAGE STICKING As an example of temporal dark boundary image sticking, Fig. 2(a) and (b) shows that when the original image patterns, including white, red, green, and blue images, were displayed for 15 min on the 42-in plasma TV, the image patterns then persisted in the subsequent dark background. As shown in the residual white image pattern in Fig. 2(b) captured from the 42-in plasma TV, the luminance of the adjacent cells was observed to be higher than that for the cells with and without image sticking. The white image region in Fig. 2(a) is the discharge region (A) shown in Fig. 3(a) where the image sticking is produced by the iterant strong sustain discharge. When the subsequent image is dark, the image-sticking cells ) (i.e., discharge region) produce brighter images (0.76 ) than the background (i.e., nondischarge region) (0.71

Fig. 2. (a) Original images displayed for 15-min, including white, red, green, and blue square patterns, and (b) corresponding residual or ghost image patterns with dark background captured on 42-in plasma TV.

mainly due to the activation of the MgO surface caused by the iterant strong sustain discharge [4]. In Fig. 3(b), the cells

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square image pattern, the boundary image sticking induced a mixed green and blue color (cyan) with the dark background, as shown in Fig. 3(b). In this case, the green and blue cells were the cells adjacent to the red cells, as shown in Fig. 4(b), and the color change from the red image into the green and blue mixed image with the dark background meant that the visible light for the green and blue cells (i.e., adjacent cells) was more intensive than that for the red cells (i.e., image-sticking cells). This boundary image-sticking phenomenon will be further discussed in a later section. IV. RESULTS AND DISCUSSION

Fig. 3. Luminance difference among regions A (discharge region), B (nondischarge regions), and C (cell adjacent to discharge region) with dark background image captured on 42-in plasma TV.

Fig. 4. Schematic diagrams of PDP cells displaying four square image patterns: (a) white, (b) red, (c) green, and (d) blue on 42-in plasma TV, where the start figure indicates discharge-on.

adjacent to the discharge region, despite being a nondischarge ), which region, produce the brightest images (0.79 causes another type of image sticking, referred to as boundary image sticking. Even though the bulge at the object boundary is small, the human visual system is still quite sensitive to the appearance of such edges in images. The detailed causes for the boundary image sticking will be discussed in a later section. In addition, for the red, green, and blue color images, the residual image sticking in Fig. 2(b) shows the different colors on the dark background. Meanwhile, Fig. 4 shows schematic diagrams of the PDP cells displaying the (a) white, (b) red, (c) green, and (d) blue images. When the displayed image was white, that is, when the R, G, and B cells were all discharged, as shown in Fig. 4(a), the boundary image sticking only induced a luminance difference with the dark background. However, when the displayed image was red, green, or blue, that is, when only one cell among the R, G, and B cells was discharged, as shown in Fig. 4(b)–(d), the boundary image sticking induced a color difference with the dark background. For example, with the red

A. Effect of Panel-Temperature Rise on IR (828-nm) Emission Characteristics in Cells Adjacent to Discharge Cells or Discharge Cells during Reset Period Fig. 5(a) shows the changes in the IR (828 nm) emission waveforms measured from the discharge cells (i.e., image-sticking cells) during the ramp-up and ramp-down periods and the magnified IR emission waveforms during the ramp-up period when the white image pattern displayed for 10–60 min was abruptly changed to a dark background. In addition, Fig. 5(a) shows the panel-temperature rise measured from the front glass of the panel for the discharge cells when the white image patterns were displayed for 10–60 min. Even the 10-min sustain discharge caused the panel temperature to rise from room temperature to 50 C, thereby affecting the reset discharge by shifting the IR emission peak to the left and broadening the IR emission waveform during the ramp-up period. The shift of the IR emission to the left implied that a weak reset discharge was efficiently initiated at a lower starting discharge voltage during the ramp-up period, while the broadening of the IR emission meant the efficient production of the reset discharge. This efficient reset discharge generation under lower voltage conditions can be mainly attributed to the activated MgO surface caused by the panel-temperature rise [10], [11]. Fig. 5(b) shows the changes in the integrated values of the IR emission waveforms calculated from the IR emission waveforms of Fig. 5(a) measured during the ramp-up and ramp-down periods form the image sticking cells. As shown in Fig. 5(b), the total amount of the IR emission was increased due to the lowering of the breakdown voltage with the temperature rise caused by the increase in the display time. The variations in both the IR emission waveform in Fig. 5(a) and the integrated value of the emitted IR waveform in Fig. 5(b) show the gradual saturation characteristics as the panel-temperature rise became saturated. Fig. 5(c) shows the recovery characteristics of the IR emissions in the discharge cells when only a reset discharge was produced after the extinction of the iterant strong sustain discharge. As shown in the IR recovery characteristics in Fig. 5(c), the IR emission characteristics only recovered their initial state when the panel temperature returned to the initial room temperature. Fig. 6(a) shows the changes in the IR (828-nm) emission waveforms measured from the cells adjacent to the discharge cells (i.e., boundary image-sticking cells) during the ramp-up and ramp-down periods and the magnified IR emission waveforms during the ramp-up period when the white image pattern displayed for 10–60 min was abruptly changed to a dark background. In addition, Fig. 6(a) shows the panel-temperature rise


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Fig. 5. (a) Changes in IR emission waveforms measured from discharge cells (i.e., image sticking cells) during ramp-up and ramp-down periods and magnified IR emission waveform during ramp-up period when white image patterns displayed for 10–60 min are abruptly changed to dark background, plus panel-temperature rise measured for discharge cells relative to display time. (b) Changes in integrated values of IR emission waveforms calculated from IR emission waveforms of Fig. 5(a) measured during ramp-up and ramp-down periods from image sticking cells. (c) Recovery characteristics of IR emission in discharge cells when only reset discharge is produced after extinction of iterant strong sustain discharge.

Fig. 6. (a) Changes in IR emission waveforms measured from cells adjacent to discharge cells (i.e., boundary image sticking cells) during ramp-up and ramp-down periods and magnified IR emission waveform during ramp-up period when white image patterns displayed for 10–60 min are abruptly changed to dark background, plus panel-temperature rise measured for cells adjacent to discharge cells relative to display time. (b) Changes in integrated values of IR emission waveforms calculated from IR emission waveforms of Fig. 6(a) measured during ramp-up and ramp-down periods from boundary image sticking cells. (c) Recovery characteristics of IR emissions in cells adjacent to discharge cells when only reset discharge is produced after extinction of iterant strong sustain discharge.

measured from the front glass of the panel for the cells adjacent to the discharge cells when the white image pattern was

displayed for 10–60 min. Similar to the results in Fig. 5(a), the 10-min sustain discharge caused the panel temperature to

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rise even in the adjacent cells from room temperature to 46 C, thereby affecting the reset discharge in the adjacent cells by shifting the IR emission peak to the left and broadening the IR emission waveform during the ram-up period. Even though the discharge was not produced in the adjacent cells, the strong sustain discharge created next to the adjacent cells induced the panel-temperature rise in the adjacent cells that was slightly lower than the panel-temperature rise in the discharge cells. As shown in Fig. 6(a), the panel-temperature rise improved the reset discharge efficiency, which increased the background luminance of the adjacent cells under dark background conditions, confirming that the main cause of temporal dark background image sticking would seem to be a panel-temperature rise. Fig. 6(b) shows the changes in the integrated values of the IR emission waveforms calculated from the IR emission waveforms of Fig. 6(a) measured during the ramp-up and ramp-down periods form the boundary image sticking cells. Similar to the results in Fig. 5(b), the total amount of the IR emission was increased due to the lowering of the breakdown voltage with the temperature rise caused by the increase in the display time. Fig. 6(c) shows the recovery characteristics of the IR emissions in the adjacent cells when only a reset discharge was produced after the extinction of the iterant strong sustain discharge. The recovery characteristics of the adjacent cells showed the same tendency as those of the discharge cells in Fig. 5(c). Fig. 7(a) shows the changes in the IR emission waveforms measured from the cells during the ramp-up and ramp-down periods and the magnified IR emission waveforms during the ramp-up period with a dark background when an external heater was used to heat the front panel at various temperatures ranging from 26 C to 61 C. Fig. 7(b) shows the changes in the integrated values of the IR emission waveforms calculated from the IR emission waveforms of Fig. 7(a) measured during the ramp-up and ramp-down periods. Similar to the results in Figs. 5(b) and 6(b), the total amount of the IR emission was increased due to the lowering of the breakdown voltage with the temperature rise caused by the external heating. Meanwhile, Fig. 7(c) shows the recovery characteristics of the IR emissions during the ramp reset period when the front panel was cooled from 61 C to 26 C. As shown in Fig. 7(a), the IR emission peak shifted to the left, implying that the breakdown voltage could simply be decreased simply raising the panel temperature without producing a strong sustain discharge. This phenomenon was almost the same as that in Figs. 5(a) and 6(a), confirming that once the panel temperature was increased due to either an iterant strong sustain discharge or heating by an external heater without a discharge effect, the corresponding breakdown voltage was decreased. As such, the lower breakdown voltage caused an increase in the IR emission during the reset period, resulting in a temporal dark image-sticking phenomenon in either the discharge cells or adjacent cells. When the reset discharge is initiated at a lower voltage, the weak reset discharge continues to be produced until the voltage reaches the setup voltage, thereby resulting in emitting the reset light during the longer time. In addition, at the falling period of the ramp voltage, the IR emission is also increased due to the fast initiation of the weak reset discharge caused by easily erasing the larger amount of the wall charges accumulated during the


Fig. 7. (a) Changes in IR emission waveforms measured from cells during ramp-up and ramp-down periods and magnified IR emission waveform during ramp-up period with dark background when using external heater to heat front panel at various temperatures ranging from 26 C to 61 C, (b) changes in integrated values of IR emission waveforms calculated from IR emission waveforms of Fig. 7(a) measured during ramp-up and ramp-down periods, and (c) recovery characteristics of IR emissions during ramp-reset period when front panel is cooled.

ramp-up period. Consequently, the initiation of the ramp reset discharge at a lower voltage means the increase in the emitted IR during the ramp-up and ramp-down periods. Furthermore, with a dark background image, the luminance of the adjacent cells (i.e., boundary image-sticking cells) was observed to be


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higher than that of the discharge cells (i.e., image-sticking cells). This phenomenon can be explained as follows: in the discharge cells, the iterant strong sustain discharge caused a deterioration of the phosphor layers, thereby degrading the luminance characteristics in the discharge cells, whereas the degradation of the phosphor layers in the adjacent cells was relatively small, as there was no sustain discharge [2]. Unlike the cases of Figs. 5 and 6, the visible spectra from the cells heated up externally shown in Fig. 7 did not show a broadening with a temperature rise. Even though the reason is not clear, it is thought that this is presumably due to the difference of the wall charge accumulation, especially on the address electrode. The in-depth investigation will be needed to explain this phenomenon more clearly. In Figs. 5–7, the most important temperature is not a temperature on the front glass but a temperature on the MgO surface. However, it is nearly impossible to measure the exact temperature on the MgO surface. In Figs. 5 and 6, the temperature rise on the front glass was caused by the iterant strong sustain discharge within the cells, whereas in Fig. 7, the temperature rise on the front glass was caused by the external heater. Consequently, even though the measured temperatures on the front glass are identical, the temperature on the MgO layer raised by the external heater must be lower than that raised by the iterant strong sustain discharge. B. Boundary Image-Sticking Phenomenon in Red, Green, and Blue Images Fig. 8(a)–(c) shows the changes in the visible spectra emitted from the red, green, and blue cells when only one color image, i.e., (a) red, (b) green, or (c) blue image, displayed for 15 min was abruptly changed to a dark background. As shown in Fig. 2(b), there are two types of boundary image sticking: one type is to show the luminance difference instead of the color change for the white image case, and the other type is to show the color change instead of the luminance difference for the single color image. The data of Fig. 8 are provided to explain the color change shown in the Fig. 2(b). In Fig. 2(b), the dark background image is displayed only through the reset discharge, but not the sustain discharge. Thus, the color change phenomenon in the boundary image sticking cells is related to the change in the visible spectra emitted in the boundary image sticking cells from the weak reset discharge during the reset period. The red, green, and blue spectra were emitted from the red, green, and blue cells, respectively. In Fig. 8, “reference” means the state before the red, green, or blue image was displayed, “0 min” means the time when the red, green, or blue image displayed for 15 min was abruptly changed to a dark background, and “5, 15, 30, and 40 min” represents the time elapsed with the dark background after the generation of image sticking. As shown in Fig. 8(a), after a 15-min sustain discharge displaying the red image, the intensities of the blue and green spectra increased by about 21% and 23%, respectively, whereas the intensity of the red spectrum only increased by about 9%. In this case, the red cells were the discharge cells, while the green and blue cells were the adjacent cells, i.e., nondischarge cells. As mentioned above, the increase in the visible spectra, especially the green and blue spectra, was due to the increased

Fig. 8. Changes in visible spectra emitted from red, green, and blue cells when only one color image, i.e., (a) red, (b) green, or (c) blue image, displayed for 15 min is abruptly changed to dark background, and changes in visible spectra with dark background after generation of image sticking.

panel temperature for the adjacent cells with no discharge. Conversely, the small increase in the red spectrum for the discharge cells was due to the phosphor degradation caused by the strong sustain discharge, despite the increase in the panel temperature. The increases in the visible spectra in Fig. 8(b) and (c) exhibited the same tendency as those in Fig. 8(a). The difference in the rate of increase for the visible spectra between the discharge cells and the adjacent cells induced the color temporal boundary image sticking, that is, a color change. After a 15-min display, the color boundary image sticking resulted in cyan (green plus blue) for the red image, magenta (red plus blue) for the green image, and yellow (red plus green) for the

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blue image with a dark background. Furthermore, Fig. 8(a)–(c) shows the changes in the visible spectra with respect to the time elapsed with a dark background after the generation of boundary image sticking, indicating that at least 40 min was needed for the natural disappearance of the boundary image sticking. V. CONCLUSION The temporal dark boundary image sticking phenomena for white, red, green, and blue images were investigated by observing the luminance and IR (828-nm) emission characteristics relative to the panel-temperature rise, and found to be closely related to the panel-temperature rise in the cells adjacent to the discharge cells. REFERENCES [1] H.-S. Tae, S.-H. Jang, J.-W. Han, B.-G. Cho, B.-N. Kim, and S.-I. Chien, “Experimental observation of image sticking in 42-inch PDP-TV,” in SID Dig., 2003, pp. 788–791. [2] H.-S. Tae, J.-W. Han, S.-H. Jang, B.-N. Kim, B. J. Shin, B.-G. Cho, and S.-I. Chien, “Experimental observation of image sticking phenomenon in AC plasma display panel,” IEEE Trans. Plasma Sci., vol. 32, no. 6, pp. 2189–2196, Dec. 2004. [3] J.-W. Han, B.-G. Cho, H.-S. Tae, S.-I. Chien, B. J. Shin, and J.-Y. Kim, “Design of facing reset discharge waveform for reducing dark image sticking in AC-PDP,” in SID Dig., 2004, pp. 532–535. [4] J.-W. Han, B.-G. Cho, K.-H. Park, J. Y. Kim, H.-S. Tae, S.-I. Chien, and B. J. Shin, “Temporal image sticking phenomena in AC-PDP with large sustain gap,” Proc. IDW, pp. 965–968, 2004. [5] H.-J. Lee, D.-H. Kim, Y.-R. Kim, M.-S. Hahm, D.-K. Lee, J.-Y. Choi, C.-H. Park, J.-W. Rhyu, J.-K. Kim, and S.-G. Lee, “Analysis of temporal image sticking in AC-PDP and the methods to reduce it,” in SID Dig., 2004, pp. 214–217. [6] J. H. Choi, Y. Jung, K. B. Jung, S. B. Kim, P. Y. Oh, H. S. Jung, K. Y. Sung, and E. H. Choi, “Influence of image sticking on electro-optical characteristics in alternating-current plasma display panels,” in Proc. IDW, 2003, pp. 913–916. [7] J. E. Lim, W. B. Park, H. S. Jeong, K. B. Jung, W. Joen, H. J. Lee, and E. H. Choi, “Influences of degradation of MgO protective layer and phosphor on ion-induced secondary electron emission coefficient and basic discharge characteristics in AC-PDP,” in Proc. IDW, 2004, pp. 1027–1030. [8] C. H. Ha, D. C. Jeong, and K. W. Whang, “A Study on the temporal bright image sticking problem in AC-PDP,” in Proc. IMID, 2004, pp. 113–116. [9] J.-W. Han, H.-S. Tae, and S.-I. Chien, “Image sticking phenomena of adjacent cells induced by iterant discharge cells in 42-in. PDP TV,” in Proc. IDW, 2003, pp. 917–920. [10] B. J. Shin, K. C. Choi, H.-S. Tae, J. H. Seo, J. Y. Y. Kim, and J.-W. Han, “Case studies on temperature-dependent characteristics in AC PDPs,” IEEE Trans. Plasma Sci., vol. 33, no. 1, pp. 162–169, Feb. 2005. [11] K.-R. Shim, C.-H. Park, and H.-J. Lee, “The effects of panel temperature on the discharge characteristics of micro discharge cells,” KIEE Int. Trans. EA, vol. 4-C, no. 5, pp. 215–219, 2004.

Jin-Won Han received the B.S. and M.S. degrees in electronic and electrical engineering from Kyungpook National University, Daegu, Korea, in 2001 and 2003, respectively. He is currently working toward the Ph.D. degree in electronic engineering at the same university. His current research interests include plasma physics and new cell structure of plasma display panels (PDPs).

Heung-Sik Tae (SM’05) received the B.S. degree in electrical engineering from Seoul National University, Seoul, Korea, in 1986 and the M.S. and Ph.D. degrees in electrical engineering from the same university, in 1988 and 1994, respectively. Since 1995, he has been an Associate Professor in the School of Electrical Engineering and Computer Science, Kyungpook National University, Daegu, Korea. His research interests include the optical characterization and driving circuit of plasma display panels (PDPs), the design of millimeter wave guiding structures, and electromagnetic wave propagation using meta-material. Dr. Tae is a member of the Society for Information Display (SID). Since 2005, he has been serving as an Editor for the IEEE TRANSACTIONS ON ELECTRON DEVICES, section on flat panel display.

Bhum Jae Shin graduated from Seoul National University, Seoul, Korea, in 1990. He received the M.S. and Ph.D. degrees in plasma engineering from Seoul National University, in 1992 and 1997, respectively. He worked on the development of PDPs as a Senior Researcher in the PDP team of Samsung SDI, Korea, from 1997 to 2000. He worked on the capillary discharges as a Research Scholar, Physics Department, Stevens Institute of Technology, Hoboken, NJ, from 2000 to 2001. In 2002, he returned to Korea, and following a one-year postdoctoral at Seoul National University, he is currently working on the development of PDPs as an Assistant Professor, Sejong University, Seoul, Korea.

Sung-Il Chien (M’90) received the B.S. degree from Seoul National University, Seoul, Korea, in 1977, the M.S. degree from the Korea Advanced Institute of Science and Technology, Seoul, in 1981, and the Ph.D. degree in electrical and computer engineering from Carnegie Mellon University, Pittsburgh, PA, in 1988. Since 1981, he has been with School of Electronic and Electrical Engineering, Kyungpook National University, Daegu, Korea, where he is currently a Professor. His research interests include digital image processing and color image processing. Dr. Chien is a member of the IEE the Society for Information Display (SID).

Dong Ho Lee was born in Pohang, Korea, on November 14, 1956. He received B.E. degree in electronics engineering from Seoul National University, Seoul, Korea, in 1979, the M.S. degree in computer science from Korea Advanced Institute of Science and Technology, Daejeon,, Korea, in 1981, and the Ph.D. degree in computer science from the University of Iowa, Iowa City, in 1992. Since March 1993, he has been with the School of Electrical Engineering and Computer Science, Kyungpook National University, Daegu. He is currently an Associate Professor. His areas of interests include designing and testing of VLSI circuits, digital TV hardware, and bioinformatics.