Every generative model leaderboard cites FID, CLIP score, and a win rate from a human-preference arena. Each number has a failure mode a determined researcher can game. If you do not know the failure modes, you cannot tell a real improvement from a gaming run.
A generative model is judged on sample quality and conditioning adherence. Neither has a closed-form measure. Your model has to render 10,000 images; something has to assign them numbers; you have to trust the numbers across model families, across resolutions, across architectures. Three metrics survived the 2014-2026 gauntlet:
FID (Fréchet Inception Distance). A distance between two distributions — real and generated — in an Inception network's feature space. Lower is better.
CLIP score. Cosine similarity between a generated image's CLIP-image embedding and a prompt's CLIP-text embedding. Higher is better. Measures prompt adherence.
Human preference. Pit two models head-to-head on the same prompt, have humans (or a GPT-4-class model) pick the better one, aggregate to an Elo score.
You will also see: IS (inception score, largely retired), KID, CMMD, ImageReward, PickScore, HPSv2, MJHQ-30k. Each corrects for one failure of the previous.
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