The development of luminance uniformity measurement for CNT-BLU based on human visual perception

Abstract

Carbon nanotube backlight units (CNT-BLUs) offer advantages (including light weight and superior color performance) that cold cathode fluorescent lamp backlight units (CCFL-BLUs) cannot deliver. If these advantages find favor with liquid crystal display manufacturers, CNT-BLUs could possibly replace CCFL-BLUs. CNT-BLU light-emitting arrays are made by a thick-film screen printing process, which can leave dark obstructions within and between pixel areas. Thus, when the pixels light up, CNT-BLU arrays can display dark blotches within one or more pixels. Existing luminance uniformity measurements, such as Video Electronics Standards Association (VESA) or International Organization for Standardization (ISO) standards, are not designed to deal with this problem. These standards are based on the luminance of multiple non-adjacent points on a display; they cannot reflect the luminance change of adjacent pixels, which is important for measuring the uniformity of CNT-BLU. This situation is aggravated since CNT-BLU is still under development and the current luminance uniformity of CNT-BLU still cannot compete with that of CCFL. This study presents a new luminance uniformity measurement, line non-uniformity, for CNT-BLU. This method was compared with VESA and U Formula with respect to human perception. A set of CNT-BLU images with different levels of mottling was presented to 18 participants. The subjective acceptance thresholds for these images were then calculated. The uniformities using VESA, U Formula, and line non-uniformity approaches for these images were also calculated and fitted to the subjective acceptance threshold. The results showed that line non-uniformity was the best to fit the acceptance threshold; its R ² ranged from 0.80 to 0.92 whereas the R ² values of VESA and U Formula ranged from 0.00 to 0.49.

摘要

碳奈米管場發射背光模組(CNT-BLU)具備許多優點 ， 例如重量輕、 較佳的顯色能力等 ， 是傳統冷陰極管背光模組(CCFL-BLUs)所無法提供的 ， 因此對液晶顯示器製造廠商在考慮市場發展性而言 ， 有可能以碳奈米管場發射背光模組取代傳統冷陰極管背光模組。 CNT-BLU之發射電極係利用厚膜網印技術印刷於陰極板上 ， 此製程有時會造成CNT漿料於像素間或像素內不正常的殘留 ， 使得CNT-BLU於點亮時形成黑影的缺陷。 現存的亮度均勻度量測方式例如 ： VESA, ISO只能反映多個散布點狀 ， 且非相連的亮度不均勻缺陷 ， 而無法反應因CNT-BLU製程造成之相鄰像素亮度不均勻的現象 ， 因此本研究提出一以CNT-BLU為基礎之亮度均勻度量測方式- Line Non-Uniformity ， 希冀能更精確的描述CNT-BLU的亮度均勻度。 此外 ， 本研究進一步透過人因工程實驗的方式 ， 以人眼感知為前提 ， 與VESA及U Formula比較。 實驗包含18位受測者 ， 施測者分別呈現各種不同缺陷嚴重程度的CNT-BLU ， 並計算其主觀接受度閾值。 結果顯示 ， 相較於VESA與U Formula, 透過Line Non-Uniformity所量測之亮度均勻度最符合受測者視覺感知(R ² = 0.80–0.92)。

(*聯絡人: [email protected])

Keywords:

• CNT-BLU
• human perception
• luminance uniformity
• threshold

Keywords:

• 關鍵字: CNT-BLU ， 人眼感知 ， 亮度均勻度 ， 閾值

Acknowledgement

This work was supported by the National Science Council under the grants NSC96-2221-E-3523.

Notes

(*聯絡人: [email protected])