Illustration of GAN-based methods for biological image reconstruction. (a) GAN, (b) pix2pix [21], (c) AmbientGAN [22], (d) cryoGAN [23]. x, y denote data in the image domain, and the measurement domain, respectively. G, D refers to generator, discriminator, respectively. H defines the function family of the forward measurement process, parameterized with φ. Networks and variables that are marked in blue have learnable parameters optimized with gradient descent.