## 3 Methodology
### Experimental Setup  
To recreate a cinematic viewing experience, a suitable viewing distance had to be chosen. The International Telecommunication Union standard for the subjective assessment of the quality of television images (ITU-R BT.500-14) [28] recommends a viewing distance of 3.2 times the height of the screen and this condition was replicated for this study. This recommendation relates to the optimum distance for assessing image quality, in which the screen inhabits a wide field of view. For the 46-inch (corner to corner) screen installed in the room where the experiment took place, this meant that the viewing position was 183 cm away from the screen. Notably, the ITU recommendation for the subjective assessment of multi-channel stereophonic sound systems with accompanying images (ITU-R BS.775-4) [29], similarly recommends 3 times the height of the screen for such studies. To decide on a suitable set of room illuminations for testing, recommendations from ITU-R BT.500-14 were used, alongside considerations for the practicality of reproduction in the room where the study took place. Three room-illumination levels were chosen to correspond to the'maximum','minimum', and 'off' settings deliverable using the lighting interface within the room. The darkest setting was representative of the illumination level considered optimal for the assessment of image quality, the medium setting was representative of a dimly lit domestic environment, and the bright setting was representative of a well-lit domestic environment [28]. The illumination conditions were measured by pointing a lux meter directly upwards towards the ceiling and then forward towards the television screen from the viewing position. For these two directions, readings were taken for the maximum and minimum light intensity, corresponding to a white and black image being shown on the screen, in all three illumination conditions. The screen brightness did not change between conditions or trials. All of these readings can be seen in Table 3. All lighting conditions were created by controlling two white light LED panels the centres of which are 1.2 m above, 1 m to the left and right, and 83 cm in front of the viewer's head. There only other light source in the room was the television screen. The experimental setup can be seen in Figure 3.  
Researchers commonly use specific webcams or specialised scientific cameras when trying to record heart rate from video (see Section 2.1). However, in this study participants were recorded using a _Panasonic Lumix DMC-FZ1000_ digital single-lens reflex (DSLR) camera (purchased in Denmark), placed discretely underneath the screen on a fixed tripod. This camera was chosen as it has an optical zoom, allowing for video to be captured at a distance without decreasing the resolution. Moreover, DSLR cameras can generally open to a wider aperture and have larger, more sensitive, sensors than webcams. This means they are more suited to capturing video footage in darker settings. This is also considered a reproducible solution, as the _Panasonic Lumix DMC-FZ1000_ is an entry-level DSLR camera \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Participant Question** & **Option** & **Frequency** & **\%** \\ \hline Gender & Female & 3 & 15 \\  & Male & 17 & 85 \\ \hline Factor in last 3 h & Nicotine & 2 & 10 \\  & Alcohol & 1 & 5 \\  & Caffeine & 13 & 65 \\  & Exercise & 1 & 5 \\  & None & 5 & 25 \\ \hline Glasses & Yes & 11 & 55 \\  & No & 9 & 45 \\ \hline Facial hair & Yes & 7 & 35 \\  & No & 13 & 65 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Description of the sample ascertained from responses to the questions presented to each participant at the start of the study. which has been commercially available since 2016. Many other DSLR cameras are capable of recording with the same, or similar, technical parameters. The 13.2 \(\times\) 8.8 mm sensor found in the _Panasonic Lumix DMC-FZ1000_ is typical of entry-level DSLR cameras. One trade-off with using a DSLR camera is that video compression is unavoidable.