{
  "taskId": "expansion-050",
  "slug": "single-light-shadow-direction",
  "language": "en",
  "mode": "image-to-video",
  "modelId": "MiniMax-H3",
  "evidenceClass": "original-practice-method-not-model-tested",
  "input": {
    "path": "/learning-assets/pseo-expansion70-20261014/single-light-shadow-direction/first-frame.png",
    "editableSource": "/learning-assets/pseo-expansion70-20261014/single-light-shadow-direction/first-frame.svg",
    "role": "first_frame",
    "sourceType": "original-illustration"
  },
  "intent": {
    "cluster": "Historical lighting, camera and image-to-video prompt family",
    "historicalQueries": [
      "minimax h3 image to video reference to video prompt setting only background camera lighting",
      "minimax h3 image to video",
      "minimax h3提示词模板"
    ],
    "evidenceRef": "docs/research/pseo-keyword-gap-2026-10-05/evidence/bing-live-keywords.csv",
    "distinctValue": "A single-light movement study on a fixed matte arch block, linking one key-light shift to one attached floor shadow while keeping camera and object still.",
    "existingOwnerBoundary": [
      {
        "path": "/blog/camera-movement-prompts",
        "difference": "This exercise holds the camera fixed and moves only one described light; it supplies a shadow scene rather than another camera vocabulary article."
      },
      {
        "path": "/blog/product-shape-consistency-video",
        "difference": "The supplied matte block isolates shadow direction and contact anchoring rather than teaching general product structure preservation."
      }
    ],
    "demandClass": "historical-parent-query; exact long-tail demand unmeasured"
  },
  "title": "Single light, one shadow: inspect direction while the object stays still",
  "description": "Move one soft key light a little toward center above a stationary object. Check that its floor shadow responds coherently without becoming a second object.",
  "goal": "Plan one modest single-light shift and judge the resulting attached shadow. The original lit illustration is a qualitative exercise, not a tested H3 relighting result or a calibrated photometric setup.",
  "preparation": [
    "Start with a matte object and one readable cast shadow on a plain surface. The supplied arch block is lit from the upper left and casts toward the lower right.",
    "Keep the object base and a ground seam visible. They let you separate changing shadow shape from an object sliding across the table.",
    "Ask the single soft key to move slightly toward the upper center, not around the full object. Avoid adding rim light, rotating the camera or changing background color.",
    "Use direction and continuity as the acceptance target. Exact shadow length, illuminance and material reflectance require measured lighting or a render, not this visual prompt."
  ],
  "prompt": "Start from the uploaded matte arch block. The block and camera remain completely fixed, with the block resting on the same tabletop contact. There is one soft key light, initially from the upper left. That one light shifts slowly a small distance toward the upper center and then stops. The single cast shadow responds smoothly, turning from lower right slightly toward lower center and becoming a little shorter, while staying attached at the block base. The lit and shaded sides change gently in agreement with that shift. Preserve the arch opening and matte surface. No second shadow, no moving object, no camera motion, no glow or extra light source.",
  "steps": [
    {
      "title": "Read the initial light-shadow pair",
      "body": "Confirm that the bright upper-left side and lower-right floor shadow are consistent in the input. A source with several competing shadows cannot isolate a single-light test."
    },
    {
      "title": "Move only the key",
      "body": "Describe a small shift toward the upper center while keeping object and camera fixed. Do not ask for a rotating product reveal; it changes the cause of the shadow movement."
    },
    {
      "title": "Follow the contact end of the shadow",
      "body": "Watch the shadow where it meets the base before judging its distant tip. It should stay anchored while its extent and direction change, rather than detach as a drifting dark shape."
    },
    {
      "title": "Cross-check surface shading",
      "body": "Compare the block face and shadow at the start and end. If one changes in the opposite sense or a second shadow appears, simplify the light shift and inspect the same relationship again."
    }
  ],
  "acceptance": [
    "The block and its tabletop contact stay fixed.",
    "The arch opening remains the same shape and stays open.",
    "There is one readable cast shadow rather than new competing shadows.",
    "The shadow remains attached at the block base.",
    "Its direction changes smoothly from lower right toward lower center.",
    "The shadow shortens slightly without teleporting or crossing through the block.",
    "Face shading changes coherently and the final light/shadow state holds still."
  ],
  "troubleshooting": [
    {
      "symptom": "The shadow floats away from the base",
      "change": "Change only the shadow attachment sentence to name the base contact; leave the light path unchanged."
    },
    {
      "symptom": "A second hard shadow appears",
      "change": "Change only the lighting description to one soft key with no additional source; keep the small movement."
    },
    {
      "symptom": "The block rotates instead of the light",
      "change": "Change only the fixed-role assignment to the block orientation and ground seam; remove product-turn wording."
    },
    {
      "symptom": "The shadow jumps to the other side",
      "change": "Reduce only the light shift so the test stays within a small directional change; compare the transition again."
    }
  ],
  "ending": "End after the light stops, with one attached shadow and a stationary arch. Record the qualitative direction check rather than claiming a measured relighting solution.",
  "assetCaption": "Original matte arch illustration with a single upper-left light and lower-right cast shadow. This is a conceptual source image, not an H3 lighting test."
}