Update app.py

app.py

@@ -156,25 +156,84 @@ def _data_uri(png_bytes: bytes) -> str:
     return "data:image/png;base64," + base64.b64encode(png_bytes).decode("ascii")
 
 
-def generate_alt_text(client, model, prompt, png_bytes, max_tokens):
-    completion = client.chat.completions.create(
-        model=model,
+ALT_TEXT_SYSTEM_PROMPT = """
+You create accessibility alt text for images.
+
+Return only the finished alt text.
+
+Requirements:
+- Write one concise sentence.
+- Describe the image's essential meaning and purpose.
+- Do not describe every minor visual detail.
+- Do not begin with "Image of", "Picture of", or "This image shows".
+- Do not include analysis, reasoning, headings, XML tags, or bullet points.
+- Do not include <think> tags.
+- Do not identify people unless their identity is explicitly provided.
+- For diagrams, summarize the main process or relationship.
+- For charts, state the chart type and principal trend or conclusion.
+- Keep the response under 250 characters when practical.
+"""
+
+def generate_alt_text(client, image_data_uri, prompt=None):
+    system_prompt = """
+You are an accessibility specialist writing alt text.
+
+Return exactly one plain-text alt description and nothing else.
+
+Rules:
+1. Do not expose reasoning or analysis.
+2. Do not use <think> tags.
+3. Do not add a heading or label.
+4. Do not begin with "Image of", "Picture of", or "This image shows".
+5. Describe the image's essential information and function.
+6. For diagrams, explain the main process or relationship rather than listing
+   every label.
+7. Include visible text only when it is necessary to understand the image.
+8. Do not speculate about unclear content.
+9. Aim for one sentence and fewer than 250 characters.
+"""
+
+    user_prompt = prompt or (
+        "Write accessible alt text for this image. "
+        "Return only the finished alt text."
+    )
+
+    response = client.chat.completions.create(
+        model="qwen/qwen3.6-27b",
+        reasoning_effort="none",
         messages=[
+            {
+                "role": "system",
+                "content": system_prompt
+            },
             {
                 "role": "user",
                 "content": [
-                    {"type": "text", "text": prompt},
                     {
-                        "type": "image_url",
-                        "image_url": {"url": _data_uri(png_bytes)},
+                        "type": "text",
+                        "text": user_prompt
                     },
-                ],
+                    {
+                        "type": "image_url",
+                        "image_url": {
+                            "url": image_data_uri
+                        }
+                    }
+                ]
             }
         ],
-        max_tokens=int(max_tokens),
         temperature=0,
+        max_tokens=100
     )
-    return (completion.choices[0].message.content or "").strip()
+
+    raw_text = response.choices[0].message.content or ""
+    cleaned_text = clean_alt_text(raw_text)
+
+    return {
+        "alt_text": cleaned_text,
+        "model_used": "qwen/qwen3.6-27b",
+        "error": ""
+    }
 
 
 def process_table(