  There are numerous approximate color transforms reported in the literature
that aim to reduce display power consumption by imperceptibly changing the
color content of displayed images. To be practical, these techniques need to be
content-aware in picking transformation parameters to preserve perceptual
quality. This work presents a computationally-efficient method for calculating
a parameter lower bound for approximate color transform parameters based on the
content to be transformed. We conduct a user study with 62 participants and
6,400 image pair comparisons to derive the proposed solution. We use the user
study results to predict this lower bound reliably with a 1.6% mean squared
error by using simple image-color-based heuristics. We show that these
heuristics have Pearson and Spearman rank correlation coefficients greater than
0.7 (p<0.01) and that our model generalizes beyond the data from the user
study. The user study results also show that the color transform is able to
achieve up to 50% power saving with most users reporting negligible visual
impairment.
