Crayon

Abstract

We present Crayon, a library and runtime system that reduces display power dissipation by acceptably approximating displayed images via shape and color transforms. Crayon can be inserted between an application and the display to optimize dynamically generated images before they appear on the screen. It can also be applied offline to optimize stored images before they are retrieved and displayed. Crayon exploits three fundamental properties: the acceptability of small changes in shape and color, the fact that the power dissipation of OLED displays and DLP pico-projectors is different for different colors, and the relatively small energy cost of computation in comparison to display energy usage.We implement and evaluate Crayon in three contexts: a hardware platform with detailed power measurement facilities and an OLED display, an Android tablet, and a set of cross-platform tools. Our results show that Crayon's color transforms can reduce display power dissipation by over 66% while producing images that remain visually acceptable to users. The measured whole-system power reduction is approximately 50%. We quantify the acceptability of Crayon's shape and color transforms with a user study involving over 400 participants and over 21,000 image evaluations.

Content-Aware Automated Parameter Tuning for Approximate Color Transforms

“…We address the challenge of finding the optimal λ, by using a computationally-efficient model, derived from a user study of acceptability of color-transformed images. The model permits color transformation methods such as Crayon [10] to automatically determine their control parameters and to do so intelligently based on the input image. In particular, this work makes the following contributions:…”

“…(2) User study: A user study with more than 6000 perceptual quality scores from 62 participants, consisting of nearly five times more bitmap images compared to the original Crayon study [10]. Results show that we are able to achieve nearly 50% display power savings with the majority of participants reporting acceptable image quality.…”

“…At the heart of Crayon is the display power model, which approximates the display power as a function of pixel value as a sum of three quadratic functions [10]. Let x be an N -pixel, RGB input image with color channels r , g, and b, and let…”

“…Crayon is the work most closely related to this work [10]. But as outlined before, the original work does not provide a way to automatically tune transform parameters, which our work addresses.…”

“…This presents new opportunities to optimize display power from software by modulating the content on the screen. Crayon [10], transforms images to reduce display power consumption by imperceptibly changing the color and shape content of images displayed. Crayon was shown to achieve up to 60% power saving while preserving image quality.…”