A graded math worksheet, then a lecture video for the mistakes

From the photo to the lecture

Original

Graded

Lecture cover

Timeline

Q9 · two boats

Q10 · circular track

The task

A user handed Xiaohe a phone photo of a child’s summer math worksheet — ten problems, each with a handwritten answer in the blank. The ask: grade it, then turn the two wrong problems into a short lecture video.

Reading the handwriting was the first hurdle. The photo is a large HEIC, the page is photographed sideways, and the answers are pencil-thin. Xiaohe rotated the page upright, then used a vision model together with local OCR to transcribe every printed problem and every handwritten answer.

Xiaohe solved all ten problems and found two errors: Q9’s second value (45 should be 49 — the two cases need both boat speeds) and Q10’s first blank (240 should be 16 — 240 is the total gap at minute 15, not the per-minute rate). It marked the photo, then built a 13-slide lecture and a 6-minute voiced video walking through both problems for an elementary student.

How Xiaohe did it

• 1. Read the photo

  HEIC → portrait orientation; Apple Vision and qwen-vl transcribe the printed problems and the handwritten answers.

• 2. Grade

  Solve all ten problems; settle two ambiguous handwritten readings by inspecting tight crops pixel by pixel.

• 3. Mark the scan

  Green ✓ on the correct answers, red circles plus the correct answers beside the two mistakes.

• 4. Build the lecture

  lecture-agent writes 13 HTML slides — river and track diagrams, a timeline, step-by-step arithmetic in large type.

• 5. Narrate

  Doubao TTS reads a 6-minute walk-through written in plain language for elementary students.

• 6. Assemble

  HTML → PNG frames and SVG → PPTX; PNG frames + page audio → 1920×1080 MP4.

• 7. QA and deliver

  Rendered the PPTX to catch text-box overflow, then shipped the video, deck, and graded image back to the source folder.

Skills used

• lecture-agent
• ppt-agent · HTML → SVG → PPTX
• Vision OCR (qwen-vl + Apple Vision)
• Doubao TTS

Deliverables