PaliGemma 2 vs SigLIP

PaliGemma 2 is a vision-language model released in December 2024 by Google DeepMind. It pairs the SigLIP-So400m vision encoder with the Gemma 2 language model family, extending the original PaliGemma architecture with stronger language capabilities and a wider set of transfer benchmarks. The model is designed primarily as a fine-tuning base rather than a chat-optimized assistant. Google releases pretrained "PT" checkpoints intended for task-specific adaptation rather than direct out-of-the-box use.

PaliGemma 2 accepts an image paired with a text prompt and generates natural language output, supporting image captioning, visual question answering, optical character recognition, document understanding, object detection and segmentation (with appropriate fine-tuning), and a range of specialized vision-language tasks. The model is released at three parameter sizes (3B, 10B, and 28B), built on the Gemma 2 2B, 9B, and 27B language backbones. Each size is available at three input resolutions: 224, 448, and 896 pixels. Alongside the base PT checkpoints, Google released PaliGemma 2 Mix variants that have been tuned on a mixture of downstream tasks to provide stronger out-of-the-box performance for common applications such as OCR and document parsing. PaliGemma 2 is distributed under the Gemma license, a custom license from Google that permits commercial use subject to the terms of the Gemma Prohibited Use Policy.

SigLIP is a vision-language model released in March 2023 by researchers at Google DeepMind. It adapts the CLIP image-text pretraining approach by replacing CLIP's softmax-based contrastive loss with a pairwise sigmoid loss, which operates independently on each image-text pair rather than requiring a global view of all pairs in a batch. This change decouples the loss from batch size, enabling more memory-efficient training and improved performance at smaller batch sizes, a regime where softmax contrastive learning typically struggles. Despite this simplification, SigLIP matches or exceeds CLIP-style models on zero-shot image classification and image-text retrieval benchmarks when trained on comparable data.

SigLIP is distributed as an image encoder plus aligned text encoder, supporting zero-shot classification with arbitrary class vocabularies, image-text retrieval, and use as a frozen backbone in downstream vision-language models. Pretrained models are available at multiple Vision Transformer sizes and input resolutions, including 224, 256, 384, and 512 pixel inputs. SigLIP is released under the Apache 2.0 license by Google and is used as the vision encoder in Google's PaliGemma and PaliGemma 2. A successor, SigLIP 2, was released in February 2025 with multilingual support across 109 languages, improvements to localization and dense prediction, and two resolution handling variants (FixRes for backward-compatible fixed resolutions and NaFlex for native aspect ratio with variable sequence length).