“Discriminability–Experimental Cost” Tradeoff in Subjective Video Quality Assessment of Codec: DCR with EVP Rating Scale Versus ACR–HR

This work uses naive observers to compare two subjective studies conducted in a controlled laboratory environment on SDR HD, UHD, and HDR UHD contents. These tests aim to compare the precision and accuracy of a modified Degradation Category Rating (DCR) and Absolute Category Rating with Hidden Reference (ACR-HR) subjective methods for video quality assessment. The modified version of the DCR method includes a repetition of both reference and distorted stimuli; and utilizes an 11-grade rating scale from Expert Viewing Protocol (EVP) of ITU-R BT.500-15 standards. In the second subjective protocol, ACR-HR operates without repetition and with the 5-grade quality scale from ITU standards. We extensively analyze the scale usage and compare Mean Opinion Score (MOS) discriminability in both subjective studies. We show that both methods can retrieve accurate MOS. However, the ACR-HR method achieves better discriminability among MOS than DCR with the EVP rating scale while reducing the experimental effort by a factor of two, i.e., the cost of the experiment. The findings of this work give new insight into how to perform cost-efficient subjective tests for video quality estimation with naive observers and how to retrieve good MOS estimates.