[Model] Add ColPali late interaction model for multi-modal retrieval

Add support for ColPali (ColBERT-style late interaction on PaliGemma
backbone) for multi-vector document retrieval and reranking.

- Model implementation extending PaliGemmaForConditionalGeneration
  with a linear projection head for per-token embeddings
- Custom ColPaliConfig extending PaliGemmaConfig with embedding
  projection fields (no trust_remote_code needed)
- Registration in model registry and config registry
- Multimodal processor handling for image+text pooling inputs
- Weight loading with support for multiple checkpoint naming
  conventions (HF transformers, colpali-engine)
- Comprehensive tests: token embedding, late interaction scoring,
  relevance ordering, and multimodal scoring
- Added to test model registry and supported models documentation

Target model: vidore/colpali-v1.3-hf
Reference: https://arxiv.org/abs/2407.01449

Signed-off-by: Nikita Sukharev <kaonael@gmail.com>

Author: Kaonael

docs/models/supported_models.md

@@ -827,6 +827,7 @@ The following table lists those that are tested in vLLM.
 | ------------ | ------ | ------ | ----------------- | -------------------- | ------------------------- |
 | `CLIPModel` | CLIP | T / I | `openai/clip-vit-base-patch32`, `openai/clip-vit-large-patch14`, etc. | | |
 | `ColModernVBertForRetrieval` | ColModernVBERT | T / I | `ModernVBERT/colmodernvbert-merged` | | |
+| `ColPaliForRetrieval` | ColPali | T / I | `vidore/colpali-v1.3-hf` | | |
 | `LlamaNemotronVLModel` | Llama Nemotron Embedding + SigLIP | T + I | `nvidia/llama-nemotron-embed-vl-1b-v2` | | |
 | `LlavaNextForConditionalGeneration`<sup>C</sup> | LLaVA-NeXT-based | T / I | `royokong/e5-v` | | ✅︎ |
 | `Phi3VForCausalLM`<sup>C</sup> | Phi-3-Vision-based | T + I | `TIGER-Lab/VLM2Vec-Full` | | ✅︎ |

tests/models/multimodal/pooling/test_colpali.py

@@ -0,0 +1,330 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Tests for ColPali late interaction model for multi-modal retrieval.
+
+ColPali is a multi-vector retrieval model based on PaliGemma backbone
+(SigLIP + Gemma) with ColBERT-style late interaction scoring (MaxSim).
+It produces per-token embeddings for both text and image inputs.
+"""
+
+import base64
+from io import BytesIO
+
+import pytest
+import torch
+from PIL import Image
+
+from vllm.entrypoints.chat_utils import (
+    ChatCompletionContentPartImageParam,
+    ChatCompletionContentPartTextParam,
+)
+from vllm.entrypoints.pooling.score.utils import ScoreMultiModalParam
+
+from ....conftest import VllmRunner
+
+MODELS = [
+    "vidore/colpali-v1.3-hf",
+]
+
+EMBED_DIMS = {
+    "vidore/colpali-v1.3-hf": 128,
+}
+
+TEXT_QUERIES = [
+    "What is the capital of France?",
+    "Describe the contents of the document.",
+]
+
+TEXT_DOCUMENTS = [
+    "The capital of France is Paris.",
+    "This document contains important financial data.",
+]
+
+DTYPE = "half"
+GPU_MEMORY_UTILIZATION = 0.7
+
+
+def _make_base64_image(
+    width: int = 64, height: int = 64, color: tuple[int, int, int] = (255, 0, 0)
+) -> str:
+    """Create a small solid-color PNG image and return its base64 data URI."""
+    img = Image.new("RGB", (width, height), color)
+    buf = BytesIO()
+    img.save(buf, format="PNG")
+    b64 = base64.b64encode(buf.getvalue()).decode()
+    return f"data:image/png;base64,{b64}"
+
+
+def _make_image_mm_param(
+    image_uri: str,
+    text: str | None = None,
+) -> ScoreMultiModalParam:
+    """Build a ScoreMultiModalParam containing an image (and optional text)."""
+    content: list = [
+        ChatCompletionContentPartImageParam(
+            type="image_url",
+            image_url={"url": image_uri},
+        ),
+    ]
+    if text is not None:
+        content.append(
+            ChatCompletionContentPartTextParam(type="text", text=text),
+        )
+    return ScoreMultiModalParam(content=content)
+
+
+def _make_text_mm_param(text: str) -> ScoreMultiModalParam:
+    """Build a ScoreMultiModalParam containing only text."""
+    return ScoreMultiModalParam(
+        content=[ChatCompletionContentPartTextParam(type="text", text=text)],
+    )
+
+
+def _run_token_embed_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Verify per-token embedding shape and L2 normalization."""
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        outputs = vllm_model.token_embed([TEXT_QUERIES[0]])
+
+        assert len(outputs) == 1
+        emb = torch.tensor(outputs[0])
+        # Token embeddings should be 2D: [num_tokens, embed_dim]
+        assert emb.dim() == 2
+        assert emb.shape[1] == EMBED_DIMS[model]
+        assert emb.shape[0] > 1
+
+        # Verify L2 normalization
+        norms = torch.norm(emb, p=2, dim=-1)
+        torch.testing.assert_close(
+            norms,
+            torch.ones_like(norms),
+            rtol=1e-2,
+            atol=1e-2,
+        )
+
+
+def _run_late_interaction_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Verify MaxSim scoring matches manual computation."""
+    from vllm.entrypoints.pooling.score.utils import compute_maxsim_score
+
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        q_outputs = vllm_model.token_embed([TEXT_QUERIES[0]])
+        d_outputs = vllm_model.token_embed([TEXT_DOCUMENTS[0]])
+
+        q_emb = torch.tensor(q_outputs[0])
+        d_emb = torch.tensor(d_outputs[0])
+
+        manual_score = compute_maxsim_score(q_emb, d_emb).item()
+
+        vllm_scores = vllm_model.score(TEXT_QUERIES[0], TEXT_DOCUMENTS[0])
+
+        assert len(vllm_scores) == 1
+        assert vllm_scores[0] == pytest.approx(manual_score, rel=0.01)
+
+
+def _run_relevance_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Verify that relevant documents score higher than irrelevant ones."""
+    query = "What is machine learning?"
+    documents = [
+        "Machine learning is a subset of artificial intelligence.",
+        "The weather forecast shows rain tomorrow.",
+        "Deep learning uses neural networks for complex tasks.",
+    ]
+
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        scores = vllm_model.score(query, documents)
+
+        assert len(scores) == 3
+        assert scores[0] > scores[1], "ML doc should score higher than weather doc"
+        assert scores[2] > scores[1], "DL doc should score higher than weather doc"
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_token_embed(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_token_embed_test(vllm_runner, model, dtype=dtype)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_late_interaction_scoring(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_late_interaction_test(vllm_runner, model, dtype=dtype)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_relevance_ordering(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_relevance_test(vllm_runner, model, dtype=dtype)
+
+
+# ── Multimodal scoring tests ────────────────────────────────
+
+
+def _run_multimodal_text_query_image_docs_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Score a text query against image documents via the multimodal path."""
+    red_image = _make_base64_image(64, 64, color=(255, 0, 0))
+    blue_image = _make_base64_image(64, 64, color=(0, 0, 255))
+
+    query = "Describe the red object"
+    image_docs = [
+        _make_image_mm_param(red_image),
+        _make_image_mm_param(blue_image),
+    ]
+
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        scores = vllm_model.llm.score(query, image_docs)
+
+        assert len(scores) == 2
+        for s in scores:
+            assert isinstance(s.outputs.score, float)
+
+
+def _run_multimodal_mixed_docs_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Score a text query against a mix of text and image documents."""
+    red_image = _make_base64_image(64, 64, color=(255, 0, 0))
+
+    query = "What is the capital of France?"
+    documents: list = [
+        "The capital of France is Paris.",
+        _make_image_mm_param(red_image),
+    ]
+
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        scores = vllm_model.llm.score(query, documents)
+
+        assert len(scores) == 2
+        for s in scores:
+            assert isinstance(s.outputs.score, float)
+        # Text document about France should score higher than a random image
+        assert scores[0].outputs.score > scores[1].outputs.score
+
+
+def _run_multimodal_image_query_text_docs_test(
+    vllm_runner: type[VllmRunner],
+    model: str,
+    *,
+    dtype: str,
+) -> None:
+    """Score an image query against text documents."""
+    red_image = _make_base64_image(64, 64, color=(255, 0, 0))
+    image_query = _make_image_mm_param(red_image, text="red color")
+
+    documents = [
+        "A bright red sports car.",
+        "The weather forecast shows rain tomorrow.",
+    ]
+
+    with vllm_runner(
+        model,
+        runner="pooling",
+        dtype=dtype,
+        max_model_len=4096,
+        enforce_eager=True,
+        gpu_memory_utilization=GPU_MEMORY_UTILIZATION,
+    ) as vllm_model:
+        scores = vllm_model.llm.score(image_query, documents)
+
+        assert len(scores) == 2
+        for s in scores:
+            assert isinstance(s.outputs.score, float)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_multimodal_text_query_image_docs(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_multimodal_text_query_image_docs_test(vllm_runner, model, dtype=dtype)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_multimodal_mixed_docs(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_multimodal_mixed_docs_test(vllm_runner, model, dtype=dtype)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", [DTYPE])
+def test_colpali_multimodal_image_query_text_docs(
+    vllm_runner,
+    model: str,
+    dtype: str,
+) -> None:
+    _run_multimodal_image_query_text_docs_test(vllm_runner, model, dtype=dtype)

tests/models/registry.py

@@ -625,6 +625,7 @@ def check_available_online(
     "ColModernVBertForRetrieval": _HfExamplesInfo(
         "ModernVBERT/colmodernvbert-merged",
     ),
+    "ColPaliForRetrieval": _HfExamplesInfo("vidore/colpali-v1.3-hf"),
     "ColQwen3": _HfExamplesInfo(
         "TomoroAI/tomoro-colqwen3-embed-4b", trust_remote_code=True
     ),