We present HiLight, a new form of real-time screen-camera communication without showing any coded images (e.g., barcodes) for off-the-shelf smart devices. HiLight encodes data into pixel translucency change atop any screen content, so that camera-equipped devices can fetch the data by turning their cameras to the screen. HiLight leverages the alpha channel, a well-known concept in computer graphics, to encode bits into the pixel translucency change. By removing the need to directly modify pixel RGB values, HiLight overcomes the key bottleneck of existing designs and enables real-time unobtrusive communication while supporting any screen content. We build a HiLight prototype using off-the-shelf smart devices and demonstrate its efficacy and robustness in practical settings. By offering an unobtrusive, flexible, and lightweight communication channel between screens and cameras, HiLight opens up opportunities for new HCI and context-aware applications, e.g., smart glasses communicating with screens to realize augmented reality.

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