GapEval: Quantifying the Gap Between Understanding and Generation Capabilities in Unified Multimodal Models

GapEval is a benchmark framework for evaluating the gap between understanding and generation capabilities in unified multimodal models, with the core goal of quantifying this gap. Research reveals that current multimodal models exhibit an imbalance where understanding capabilities are significantly superior to generation capabilities. This framework provides a systematic analysis tool for the research community and has been open-sourced.

In recent years, unified multimodal large models have become an important direction in AI. Unlike specialized models, they handle both understanding and generation tasks across multiple modalities through a single architecture. Typical models include GPT-4V/GPT-4o, Gemini, LLaVA, Qwen-VL, etc. Architecturally, they use a visual encoder to convert images into tokens, which are then input into a Transformer together with text tokens. However, key questions have been overlooked: Does a unified architecture mean unified capabilities? Are there systematic differences in performance between understanding and generation tasks?

The core goal of GapEval is to quantify the gap between understanding and generation capabilities in unified multimodal models. Evaluation dimensions are divided into understanding and generation: Understanding capabilities include visual question answering (VQA), visual reasoning, fine-grained recognition, and commonsense reasoning; Generation capabilities include image description, detailed description, and controllable generation. The evaluation methodology uses paired task design (testing both types of tasks on the same set of images), multi-dimensional metrics (automatic + human evaluation), and fine-grained analysis (by image category and other dimensions).

Through GapEval evaluation, the following findings were made: 1. Understanding is stronger than generation: Most models achieve high accuracy in understanding tasks (e.g., VQA), while outputs of generation tasks (e.g., image description) are generalized and templated; 2. Generation quality bottlenecks: Homogenized descriptions, missing details, and hallucination issues; 3. Architectural roots: Imbalanced training data (more abundant understanding data), differences in task objectives (clear answers for understanding), and architecture design biased towards information extraction rather than generation.

Guidance for model development: Balanced training strategies (emphasizing the quality of generation data), architecture optimization (visual encoding suitable for generation), and improved evaluation standards (fine-grained generation metrics). Implications for applications: Task selection (prioritize understanding tasks in key scenarios), expectation management (understanding capability boundaries), and human-machine collaboration (leveraging the strengths of model understanding and human creativity).

Open-source contributions include standardized evaluation benchmarks (unified protocols and datasets), analysis tools (automated scripts + visualization tools), and baseline results (evaluation data for mainstream models). Usage scenarios: Capability gap analysis during model development, model selection comparison, capability diagnosis, and progress tracking.

Current limitations: Insufficient data coverage (specialized data needed for specific domains), evaluation metrics (automatic metrics struggle to capture generation quality), and dynamic capabilities (models evolve rapidly requiring continuous updates). Future directions: Narrowing the capability gap (training methods to improve generation capabilities), fine-grained understanding analysis, cross-modal alignment optimization, and evaluation method innovation (more accurate generation metrics).

GapEval reveals the significant gap between understanding and generation capabilities in unified multimodal models, with academic value and application guidance significance. Current models have made significant progress in understanding tasks, but there is still room for improvement in generation tasks, reminding us to pay attention to optimizing specific tasks. GapEval's open-source provides tools for the community, promoting the development of models towards balanced and reliable directions, and we look forward to the next generation of more coordinated multimodal systems.