Every student has a powerful wireless signal transmitter, his or her cell phone, that can be used to replace the “clicker” as a personal response device. Our mobile phone-based response system (iQlickers) collects and analyzes the answers or opinions sent in by the students as SMS (short message service) messages. The statistic of the answers is displayed online in the lecture hall. On the basis of the statistic, group discussion and peer instruction can be conducted. No setup in the lecture halls and purpose-built response pads (clickers) or receivers are needed. The operation cost of our system is very low, but class interaction can be greatly enhanced.

Two dimensional (2D) barcodes are becoming a pervasive interface for mobile devices, such as camera smartphones. Often, only monochrome 2D-barcodes are used due to their robustness in an uncontrolled operating environment of smartphones. Nonetheless, we are seeing an emerging use of color 2D-barcodes for camera smartphones. Most smartphones capture and store such 2D-barcode images in the baseline JPEG format. As a lossy compression technique, JPEG does introduce a fair amount of error in the captured 2D-barcode images. In this paper, we analyzed the Discrete Cosine Transform (DCT) coefficient distributions of generalized 2D-barcodes using colored data cells, each comprising of 4, 8 and 10 colors. Using these DCT distributions, we improved the JPEG compression of such mobile barcode images. By altering the JPEG compression parameters based on the DCT coefficient distribution of the barcode images, our improved compression scheme produces JPEG images with higher PSNR value as compared to the baseline implementation. We have also applied our improved scheme to a 10 colors 2D-barcode system; and analyzed its performance in comparison to the default and alternative JPEG schemes. We have found that our improved scheme does provide a marked improvement for the successful decoding of the 10 colors 2D-barcode system.