Dynamic-Net: Tuning the Objective Without Re-Training for Synthesis Tasks

Alon Shoshan     Roey Mechrez     Lihi Zelnik-Manor

Technion – Israel Institute of Technology

ICCV 2019 [Paper]        [Supplementary]        Code [GitHub]

Dynamic-Net: We propose an approach that enables traversing the “objective-space”, spanned by two different objectives, at test-time, without re-training, as illustrated by the blue dot moving along the blue curve in the plot. This is different from the common practice of training a separate network for each objective, represented by X’s on the plot. Using a single Dynamic-Net we can tune the level of stylization of an image, monitor completion quality per image, or control facial attributes, all interactively at test-time, without re-training.



One of the key ingredients for successful optimization of modern CNNs is identifying a suitable objective. To date, the objective is fixed a-priori at training time, and any variation to it requires re-training a new network. In this paper we present a first attempt at alleviating the need for re-training. Rather than fixing the network at training time, we train a “Dynamic-Net” that can be modified at inference time. Our approach considers an “objective-space” as the space of all linear combinations of two objectives, and the Dynamic-Net is emulating the traversing of this objective-space at test-time, without any further training. We show that this upgrades pre-trained networks by providing an out-of-learning extension, while maintaining the performance quality. The solution we propose is fast and allows a user to interactively modify the network, in real-time, in order to obtain the result he/she desires. We show the benefits of such an approach via several different applications.


Proposed framework: Our training has two steps: (i) First the “main” network \(\theta\) (green blocks) is trained to minimize \({\cal O}_0\). (ii) Then \(\theta\) is fixed, one or more tuning-blocks \(\psi\) are added (orange block), and trained to minimize \({\cal O}_1\). The output \(\hat y_1\) approximates the output \(y_1\) one would get from training the main network \(\theta\) with objective \({\cal O}_1\). At test-time, we can emulate results equivalent to a network trained with objective \({\cal O}_m\) by tuning the parameter \(\alpha_m\) (in blue) that determines the latent representation \(z_m\). Our method can be applied as (a) a single-block framework or as (b) multi-block framework.



Dynamic Style Transfer

Control over Stylization level

Interpolation between two Styles

Dynamic DC-GAN: Controlled Image Generation

The proposed method allow us to generate faces with control over the facial attributes e.g gender or hair color.

Image Completion

Input \(\alpha=0\) \(\alpha=0.4\) \(\alpha=1\)     Input \(\alpha=0\) \(\alpha=0.5\) \(\alpha=1\)
Original result Improved result     Original result Improved result

Dynamic-Net allows the user to select the best working point for each image, improving results of networks that were trained with sub-optimal objectives.


Dynamic-Net: Tuning the Objective Without Re-Training for Synthesis Tasks

Paper [pdf]

Supplementary [pdf]


Try Our Code

Code and demo of the the experiments described in our paper is available in [GitHub]


Dynamic style transfer demo