Visual attention as a dimension of QoE: Subtitles in UHD videos

With the ever-growing availability of multimedia content produced, broadcast and consumed worldwide, subtitling is becoming an essential service to quickly share understandable content. Simultaneously, the increased resolution of the ultra high definition (UHD) standard comes with wider screens and new viewing conditions. Services as the display of subtitles thus require adaptation to better fit the new induced viewing visual angle. This paper aims at evaluating quality of experience of subtitled movies in UHD to propose guidelines for the appearance of subtitles. From an eye-tracking experiment conducted on 68 observers and 30 video sequences, viewing behavior and visual saliency are analyzed with and without subtitles and for different subtitle styles. Various metrics based on eye-tracking data, such as the Reading Index for Dynamic Texts (RIDT), are computed to objectively measure the ease of reading and subtitle disturbance. The results mainly show that doubling the visual angle of subtitles from HD to UHD guarantees subtitle readability without compromising the enjoyment of the video content.