DeepPrivacy: A Generative Adversarial Network for Face Anonymization

Abstract

We propose a novel architecture which is able to automatically anonymize faces in images while retaining the original data distribution. We ensure total anonymization of all faces in an image by generating images exclusively on privacy-safe information. Our model is based on a conditional generative adversarial network, generating images considering the original pose and image background. The conditional information enables us to generate highly realistic faces with a seamless transition between the generated face and the existing background. Furthermore, we introduce a diverse dataset of human faces, including unconventional poses, occluded faces, and a vast variability in backgrounds. Finally, we present experimental results reflecting the capability of our model to anonymize images while preserving the data distribution, making the data suitable for further training of deep learning models. As far as we know, no other solution has been proposed that guarantees the anonymization of faces while generating realistic images.

Appendix A - Training Details

We use the same hyperparameters as Karras et al. [12], except the following: We use a batch size of 256, 256, 128, 72 and 48 for resolution 8, 16, 32, 64, and 128. We use a learning rate of 0.00175 with the Adam optimizer. For each expansion of the network, we have a transition and stabilization phase of 1.2M images each. We use an exponential running average for the weights of the generator as this improves overall image quality [28]. For the running average, we use a decay $\beta$ given by:

$$\begin{aligned} \beta = 0.5^{\frac{B}{10^4}}, \end{aligned}$$

(1)

where B is the batch size. Our final model was trained for 17 days on two NVIDIA V100-32 GB GPUs.

Image Pre-processing

Figure 7 shows the input pre-processing pipeline. For each detected face with a bounding box and keypoint detection, we find the smallest possible square bounding box which surrounds the face bounding box. Then, we resize the expanded bounding box to the target size ($128 \times 128$). We replace the pixels within the face bounding box with a constant pixel value of 128. Finally, we shift the pixel values to the range $[-1, 1]$.

Tensor Core Modifications

To utilize tensor cores in NVIDIA’s new Volta architecture, we do several modifications to our network, following the requirements of tensor cores. First, we ensure that each convolutional block use number of filters that are divisible by 8. Secondly, we make certain that the batch size for each GPU is divisible by 8. Further, we use automatic mixed precision for pytorch [21] to significantly improve our training time. We see an improvement of $220\%$ in terms of training speed with mixed precision training.

Fig. 7.

Input Pipeline: Each detected face is cropped to a quadratic image, then we replace the privacy-sensitive information with a constant value, and feed it to the generator. The keypoints are represented as a one-hot encoded image.