Visual text compression is an emerging paradigm for rendering text as images for processing by vision-language models (VLMs), enabling higher information density per context token. However, the robustness of VLMs under dense, text-based visual inputs remains unevaluated. We introduce Fico, a benchmark designed to assess VLM robustness across seven controlled variants of visual fidelity and information density. Fico spans documents of 8k to 64k tokens and includes three tasks of increasing semantic granularity: optical character recognition (OCR), needle-in-a-haystack (NIAH) retrieval, and visual question answering (VQA). Evaluating 13 general-purpose VLMs and 3 OCR-specialized models reveals three consistent trends: performance drops sharply under increased density or reduced resolution; cross-task transfer between OCR, NIAH, and VQA is limited; and VQA is comparatively robust because low-level details are lost before high-level semantics. By exposing failure modes that remain invisible under conventional VLM evaluations, Fico establishes a rigorous test-bed for visual text compression.

We present a novel visual instruction tuning strategy to improve the zero-shot task generalization of multimodal large language models by building a firm text-only knowledge base. Existing work lacks sufficient experimentation on the importance of each modality in the instruction tuning stage, often using a majority of vision-language data while keeping text-only data limited and fixing mixtures of modalities. By incorporating diverse text-only data in the visual instruction tuning stage, we vary vision-language data in various controlled experiments to investigate the importance of modality in visual instruction tuning. Our comprehensive evaluation shows that the text-heavy instruction tuning approach is able to perform on par with traditional vision-heavy mixtures on both modalities across 12 general datasets while using as low as half the total training tokens. We find that simply increasing sufficiently diverse text-only data enables transfer of instruction following ability and domain knowledge across modalities while being more efficient than the vision-language approach.