  Image coding for machines (ICM) aims at reducing the bitrate required to
represent an image while minimizing the drop in machine vision analysis
accuracy. In many use cases, such as surveillance, it is also important that
the visual quality is not drastically deteriorated by the compression process.
Recent works on using neural network (NN) based ICM codecs have shown
significant coding gains against traditional methods; however, the decompressed
images, especially at low bitrates, often contain checkerboard artifacts. We
propose an effective decoder finetuning scheme based on adversarial training to
significantly enhance the visual quality of ICM codecs, while preserving the
machine analysis accuracy, without adding extra bitcost or parameters at the
inference phase. The results show complete removal of the checkerboard
artifacts at the negligible cost of -1.6% relative change in task performance
score. In the cases where some amount of artifacts is tolerable, such as when
machine consumption is the primary target, this technique can enhance both
pixel-fidelity and feature-fidelity scores without losing task performance.
