Automatic pain intensity estimation plays a pivotal role in healthcare and
medical fields. While many methods have been developed to gauge human pain
using behavioral or physiological indicators, facial expressions have emerged
as a prominent tool for this purpose. Nevertheless, the dependence on labeled
data for these techniques often renders them expensive and time-consuming. To
tackle this, we introduce the Adaptive Hierarchical Spatio-temporal Dynamic
Image (AHDI) technique. AHDI encodes spatiotemporal changes in facial videos
into a singular RGB image, permitting the application of simpler 2D deep models
for video representation. Within this framework, we employ a residual network
to derive generalized facial representations. These representations are
optimized for two tasks: estimating pain intensity and differentiating between
genuine and simulated pain expressions. For the former, a regression model is
trained using the extracted representations, while for the latter, a binary
classifier identifies genuine versus feigned pain displays. Testing our method
on two widely-used pain datasets, we observed encouraging results for both
tasks. On the UNBC database, we achieved an MSE of 0.27 outperforming the SOTA
which had an MSE of 0.40. On the BioVid dataset, our model achieved an accuracy
of 89.76%, which is an improvement of 5.37% over the SOTA accuracy. Most
notably, for distinguishing genuine from simulated pain, our accuracy stands at
94.03%, marking a substantial improvement of 8.98%. Our methodology not only
minimizes the need for extensive labeled data but also augments the precision
of pain evaluations, facilitating superior pain management.

通过自适应分层时空动态图像（Adaptive Hierarchical Spatio-temporal Dynamic Image，AHDI）技术，我们在医疗保健和医学领域中引入了自动疼痛强度估计方法。该方法使用面部表情作为主要工具，利用 AHDI 将面部视频的时空变化编码为一个单一的 RGB 图像，并应用简化的二维深度模型进行视频表征。该技术框架中，我们采用残差网络来获得面部的广义表征，并针对两个任务进行优化：疼痛强度估计和真实与模拟疼痛表达的区分。方法在两个广泛使用的疼痛数据集上进行测试，在两个任务上均取得了令人鼓舞的结果。除了最小化对大量标记数据的需求外，我们的方法还提高了疼痛评估的精度，提供了更好的疼痛管理。