Difficulty, Diversity, and Plausibility: Dynamic Data-Free Quantization

Without access to the original training data, data-free quantization (DFQ) aims to recover the performance loss induced by quantization. Most previous works have focused on using an original network to extract the train data information, which is instilled into surrogate synthesized images. However, existing DFQ methods do not take into account important aspects of quantization: the extent of a computational-cost-and-accuracy trade-off varies for each image, depending on its task difficulty. To handle such varying trade-offs, several efforts have been made to dynamically allocate bit-widths for each image. Such dynamic quantization, however, remains challenging and unexplored in the data-free domain, because synthesized images of previous works fail to possess properties in natural test images that are crucial for learning the appropriate dynamic allocation policy: difficulty, its diversity, and its plausibility. By contrast, we propose a data-free quantization framework that is dynamic-friendly, by modeling varying extents of task difficulties with plausibility. We generate plausibly difficult images with soft labels, whose probabilities are allocated to a group of similar classes. Images with diverse and plausible difficulties enable us to train the framework to dynamically handle the varying trade-offs. Consequently, our framework achieves better accuracy-complexity Pareto front than existing data-free quantization approaches.