On-chip frame memory reduction using a high-compression-ratio codec in the overdrives of liquid-crystal displays

Abstract

Overdrive is commonly used to reduce the liquid-crystal re- sponse time and motion blur in liquid-crystal displays (LCDs). However, overdrive requires a large frame memory in order to store the previous frame for reference. In this paper, a high-compression-ratio codec is pre- sented to compress the image data stored in the on-chip frame mem- ory so that only 1 Mbit of on-chip memory is required in the LCD over- drives of mobile devices. The proposed algorithm further compresses the color bitmaps and representative values (RVs) resulting from the block truncation coding (BTC). The color bitmaps are represented by a lumi- nance bitmap, which is further reduced and reconstructed using median filter interpolation in the decoder, while the RVs are compressed using adaptive quantization coding (AQC). Interpolation and AQC can provide three-level compression, which leads to 16 combinations. Using a rate- distortion analysis, we select the three optimal schemes to compress the image data for video graphics array (VGA), wide-VGA LCD, and standard- definitionTV applications. Our simulation results demonstrate that the pro- posed schemes outperform interpolation BTC both in PSNR (by 1.479 to 2.205 dB) and in subjective visual quality. C 2010 Society of Photo-Optical Instru-