[bug fix] Fix llava next feature size calculation. (#6339)

Signed-off-by: Xiaowei Jiang <xwjiang2010@gmail.com>

tests/models/test_llava_next.py

 from typing import List, Optional, Tuple
 
 import pytest
-from transformers import AutoTokenizer
+from transformers import AutoConfig, AutoTokenizer
 
+from vllm.model_executor.models.llava_next import (
+    get_llava_next_image_feature_size)
 from vllm.multimodal.utils import rescale_image_size
 from vllm.sequence import SampleLogprobs
 
@@ -120,3 +122,13 @@ def test_models(hf_runner, vllm_runner, image_assets, model, size_factors,
             name_0="hf",
             name_1="vllm",
         )
+
+
+@pytest.mark.parametrize("height_and_width_and_result", [(1669, 2560, 2144),
+                                                         (183, 488, 776)])
+def test_image_feature_size(height_and_width_and_result):
+    height, width, result = height_and_width_and_result
+    config = AutoConfig.from_pretrained("llava-hf/llava-v1.6-mistral-7b-hf")
+    assert get_llava_next_image_feature_size(config,
+                                             input_height=height,
+                                             input_width=width) == result

vllm/model_executor/models/llava_next.py

@@ -74,19 +74,21 @@ def _get_llava_next_num_unpadded_features(
 ) -> Tuple[int, int]:
     current_height = npatches * num_patch_height
     current_width = npatches * num_patch_width
+    current_height = torch.tensor(current_height).to("cuda")
+    current_width = torch.tensor(current_width).to("cuda")
 
     aspect_ratio: float = width / height
     current_aspect_ratio: float = current_width / current_height
     if aspect_ratio > current_aspect_ratio:
-        new_height = (height * current_width) // width
-        if new_height % 2 == 1:
-            new_height += 1
-        current_height = new_height
+        scale_factor = current_width / width
+        new_height = int(height * scale_factor)
+        padding = (current_height - new_height) // 2
+        current_height -= padding * 2
     else:
-        new_width = (width * current_height) // height
-        if new_width % 2 == 1:
-            new_width += 1
-        current_width = new_width
+        scale_factor = current_height / height
+        new_width = int(width * scale_factor)
+        padding = (current_width - new_width) // 2
+        current_width -= padding * 2
 
     unpadded_features = current_height * current_width
     newline_features = current_height