In this chapter, we propose a two-step process for automatically colorizing grayscale images with high fidelity and explainability. First, grayscale images are converted to color images using an encoder–decoder model combined with a PatchGAN discriminator. Skip connections help preserve local details, while the adversarial mechanism contributes to the sharpness and naturalness of the colors. Next, we integrate the Grad-CAM technique to visualize the model’s decision-making process. Using gradients of two chroma channels, a and b, as weights, we generate heatmaps that highlight the image regions to which the network pays special attention during the colorization process. Experimental results in the COCO-Stuff and DIV2K datasets demonstrate that the method achieves competitive performance in terms of PSNR, SSIM, and DISTS, while preserving transparent textures and edges, as indicated by qualitative evaluation. The built-in explanation module not only sheds light on the internal working mechanism of the network but also lays the foundation for the development of interactive and customizable colorization systems.

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Interpretable Grayscale Image Colorization via U-Net-GAN and Gradient-Based Attention

  • Nhu-Tai Do,
  • Tinh Vu Duc,
  • Quoc-Huy Nguyen

摘要

In this chapter, we propose a two-step process for automatically colorizing grayscale images with high fidelity and explainability. First, grayscale images are converted to color images using an encoder–decoder model combined with a PatchGAN discriminator. Skip connections help preserve local details, while the adversarial mechanism contributes to the sharpness and naturalness of the colors. Next, we integrate the Grad-CAM technique to visualize the model’s decision-making process. Using gradients of two chroma channels, a and b, as weights, we generate heatmaps that highlight the image regions to which the network pays special attention during the colorization process. Experimental results in the COCO-Stuff and DIV2K datasets demonstrate that the method achieves competitive performance in terms of PSNR, SSIM, and DISTS, while preserving transparent textures and edges, as indicated by qualitative evaluation. The built-in explanation module not only sheds light on the internal working mechanism of the network but also lays the foundation for the development of interactive and customizable colorization systems.