  When the training dataset comprises a 1:1 proportion of dogs to cats, a
generative model that produces 1:1 dogs and cats better resembles the training
species distribution than another model with 3:1 dogs and cats. Can we capture
this phenomenon using existing metrics? Unfortunately, we cannot, because these
metrics do not provide any interpretability beyond "diversity". In this
context, we propose a new evaluation protocol that measures the divergence of a
set of generated images from the training set regarding the distribution of
attribute strengths as follows. Single-attribute Divergence (SaD) measures the
divergence regarding PDFs of a single attribute. Paired-attribute Divergence
(PaD) measures the divergence regarding joint PDFs of a pair of attributes.
They provide which attributes the models struggle. For measuring the attribute
strengths of an image, we propose Heterogeneous CLIPScore (HCS) which measures
the cosine similarity between image and text vectors with heterogeneous initial
points. With SaD and PaD, we reveal the following about existing generative
models. ProjectedGAN generates implausible attribute relationships such as a
baby with a beard even though it has competitive scores of existing metrics.
Diffusion models struggle to capture diverse colors in the datasets. The larger
sampling timesteps of latent diffusion model generate the more minor objects
including earrings and necklaces. Stable Diffusion v1.5 better captures the
attributes than v2.1. Our metrics lay a foundation for explainable evaluations
of generative models.
