app.py

import gradio as gr
from PIL import Image
from transformers import (
    BlipProcessor,
    BlipForConditionalGeneration,
    AutoTokenizer,
    AutoModelForSeq2SeqLM
)
import torch

# -------- Load Models -------- #

blip_processor = BlipProcessor.from_pretrained(
    "Salesforce/blip-image-captioning-base"
)
blip_model = BlipForConditionalGeneration.from_pretrained(
    "Salesforce/blip-image-captioning-base"
)

seo_tokenizer = AutoTokenizer.from_pretrained(
    "google/flan-t5-base"
)
seo_model = AutoModelForSeq2SeqLM.from_pretrained(
    "google/flan-t5-base"
)

# -------- Core Function -------- #

def generate_alt_text(image, seo_mode, keywords):
    if image is None:
        return ""

    # ---- Step 1: Base Caption ---- #
    inputs = blip_processor(image, return_tensors="pt")

    with torch.no_grad():
        output = blip_model.generate(
            **inputs,
            max_new_tokens=30
        )

    base_caption = blip_processor.decode(
        output[0],
        skip_special_tokens=True
    ).strip()

    # ---- Step 2: Normal Mode ---- #
    if not seo_mode:
        return base_caption.capitalize() + "."

    # ---- Step 3: SEO Prompt ---- #
    keywords = keywords.strip()

    keyword_instruction = (
        f"Include the following keywords naturally: {keywords}. "
        if keywords else ""
    )

    prompt = (
        "You are an SEO expert. "
        "Write a detailed, descriptive, and natural alt text for a website image. "
        "The alt text should be longer than the original caption and written in a single sentence. "
        f"{keyword_instruction}"
        f"Image description: {base_caption}."
    )

    seo_inputs = seo_tokenizer(
        prompt,
        return_tensors="pt",
        truncation=True
    )

    # ---- Step 4: Force Expansion ---- #
    with torch.no_grad():
        seo_output = seo_model.generate(
            **seo_inputs,
            max_new_tokens=120,
            do_sample=True,
            top_p=0.95,
            temperature=1.0
        )

    seo_alt_text = seo_tokenizer.decode(
        seo_output[0],
        skip_special_tokens=True
    ).strip()

    return seo_alt_text

# -------- Gradio UI -------- #

with gr.Blocks(title="Alt Text Generator") as demo:
    gr.Markdown("""
    # 🖼️ Alt Text Generator
    AI-powered alt text for accessibility and SEO.
    """)

    image_input = gr.Image(
        type="pil",
        label="Upload Image"
    )

    seo_toggle = gr.Checkbox(
        label="SEO Mode (expanded, keyword-aware alt text)",
        value=False
    )

    keyword_input = gr.Textbox(
        label="Keywords (optional)",
        placeholder="e.g. science experiment for kids, STEM education"
    )

    alt_text_output = gr.Textbox(
        label="Generated Alt Text",
        lines=6
    )

    generate_btn = gr.Button("Generate Alt Text 🚀")

    generate_btn.click(
        fn=generate_alt_text,
        inputs=[image_input, seo_toggle, keyword_input],
        outputs=alt_text_output
    )

demo.launch()