Color Electronic Paper With Front Light

Color electronic paper (CEP) can be created by laminating a color filter array (CFA) film onto a black-and-white electrophoretic display (EPD). This technique was proposed many years ago, but it has not gained significant traction in the consumer market due to the CFA film reducing overall lightness. To address this issue, a promising solution involves directly printing color inks onto the EPD. In addition, overall brightness and color saturation are further enhanced by equipping the CEP with a front light (FL) panel, which consists of red, green, and blue light-emitting diodes (LEDs). The FL produces better visual outcomes when carefully controlled based on the image content. The color gamut of the CEP can be adjusted based on the FL settings. However, methods for determining the best FL settings and ensuring optimal color reproduction have not been thoroughly studied. This article introduces a comprehensive signal processing system for this new type of CEP. First, the color gamuts of the CEP under different LED settings of the FL are measured and estimated. Since it is impractical to measure the color gamut for every possible FL setting, we propose a new approach to estimating color gamuts for unmeasured cases. Next, the optimal LED setting is selected based on the image content. An optimal search process is applied to expedite the determination of FL settings based on the pixel colors in the image. Finally, color reproduction, including gamut mapping, is performed to align with the selected FL setting, optimizing the visual quality of the input image.