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Running on Zero
| title: Chandra OCR 2 | |
| emoji: 📄 | |
| colorFrom: indigo | |
| colorTo: purple | |
| sdk: gradio | |
| app_file: app.py | |
| pinned: false | |
| license: apache-2.0 | |
| short_description: Layout-aware document OCR to markdown + extracted figures | |
| models: | |
| - datalab-to/chandra-ocr-2 | |
| tags: | |
| - ocr | |
| - document-ai | |
| - vision-language | |
| suggested_hardware: zero-a10g | |
| # Chandra OCR 2 — Space demo | |
| Gradio demo for [`datalab-to/chandra-ocr-2`](https://huggingface.co/datalab-to/chandra-ocr-2), | |
| Datalab's layout-aware document OCR model. Upload PDFs or images and get back | |
| markdown with tables, math, forms, and reading order preserved — **plus** a | |
| separate figure-extraction stage that crops charts, diagrams, photos and stamps | |
| at full resolution and reports the model's caption and any structured data it | |
| read from them. | |
| ## Hardware | |
| **This will not run on the free CPU tier.** The model is ~10B parameters, | |
| roughly 20 GB in bf16. | |
| | Hardware | Works? | | |
| |---|---| | |
| | CPU basic (free) | No — OOM at load | | |
| | ZeroGPU (H200 slice) | Yes — recommended | | |
| | RTX PRO 6000 (Blackwell, sm_120) | Yes | | |
| | L40S / A100 | Yes | | |
| | T4 (16 GB) | No, unless you add 4-bit quantisation | | |
| Set this under **Settings → Hardware** after creating the Space. | |
| `suggested_hardware` in the frontmatter is only a hint to visitors; it does not | |
| provision anything. | |
| ## How it works | |
| - PDFs are rasterised page by page with PyMuPDF (no poppler/apt needed). | |
| - Each page is capped on its long edge before inference — visual token count | |
| scales with area, so this is the main lever on latency and memory. | |
| - Pages are batched `PAGES_PER_GPU_CALL` at a time so each ZeroGPU allocation | |
| finishes inside its duration budget. | |
| - **Stage 1 (text):** raw layout output → markdown via `parse_markdown`. | |
| - **Stage 2 (figures):** `parse_chunks` locates figure-like blocks, which are | |
| cropped from the **full-resolution** source page (the bbox is per-axis | |
| normalised, so it maps cleanly onto any resolution with the same aspect | |
| ratio). Captions and structured data come from the model's layout output and | |
| are labelled **degraded** when the fallback path was used. | |
| Output is offered as rendered markdown, markdown source, the raw model string, | |
| a figure gallery + metadata table, a combined `.md`, and a `.zip` containing | |
| per-page markdown, per-page raw output, extracted figure images, and a | |
| `manifest.json`. | |
| The app prefers the official `chandra` package (`generate_hf` + `BatchInputItem` | |
| + `parse_markdown` + `parse_chunks`). If that import fails, it falls back to | |
| driving the chat template through plain `transformers` so the Space still boots | |
| — and reports the degradation in the status panel and diagnostics. | |
| ## Configuration | |
| Edit the constants at the top of `app.py`: | |
| | Constant | Default | Purpose | | |
| |---|---|---| | |
| | `PAGES_PER_GPU_CALL` | 3 | Pages per ZeroGPU allocation | | |
| | `GPU_DURATION` | 180 | Seconds requested per allocation | | |
| | `MAX_PAGES` | 20 | Per-run page cap | | |
| Prompt types are **enumerated from the package** (`PROMPT_MAPPING`), not | |
| hardcoded. Only `ocr_layout` and `ocr` are currently exposed; the dropdown is | |
| editable so you can try undocumented values. | |
| ## Troubleshooting | |
| | Symptom | Cause / fix | | |
| |---|---| | |
| | Space won't start, opaque "upload failed" | Model load failed at import — the diagnostics panel auto-opens with the exact error. | | |
| | `CUDA out of memory` per page | Lower **Max image side**; it's the biggest VRAM lever. | | |
| | No figures in the gallery | The model returned no figure bboxes for this prompt type, or the `chandra` package is unavailable (outputs marked degraded). | | |
| | `flash-attn` build error | Do **not** add flash-attn — Blackwell (sm_120) has no prebuilt wheels. SDPA is used. | | |
| | `torch` version mismatch | Do **not** pin torch — the Space image ships a build matched to the driver/CUDA. | | |
| ## Licence — read before making this public | |
| The Space **code** here is Apache-2.0. The **model weights** are not: | |
| > Code is Apache 2.0. Model weights are under a modified OpenRAIL-M license. | |
| > Free for research, personal use, and startups under $2M funding/revenue. | |
| > Cannot be used competitively with our API. | |
| A public, free, hosted OCR endpoint is plausibly "competitive with our API." | |
| If you are past the revenue threshold, or intend this as a product rather than a | |
| demo, check with Datalab first. Setting the Space to **private** avoids the | |
| question entirely. |