sky-map-team/stardroid-v1/.claude/skills/celestial-image

Sky Map Celestial Info Card Image

Convert and size an image for use in a Sky Map celestial info card.

Target Spec

• Size: 480 × 800 px (portrait)
• Format: WebP (lossy, quality 80) — smallest file for photographic content
• Location: app/src/main/assets/celestial_images/<category>/<name>.webp
• Referenced in: object_info.json as "imageKey": "<category>/<name>.webp"

Arguments

$ARGUMENTS may contain (all optional — prompt for missing ones):

1. Source image — a local file path or a URL
2. Output path relative to celestial_images/ — e.g. messier/hubble_m1 or stars/eso_sirius (.webp extension added automatically)
3. Crop region x1,y1,x2,y2 in source-image pixels

Step 1 — Gather and validate inputs

If $ARGUMENTS is empty, ask the user:

1. Source image — local path or URL
2. Output path — <category>/<filename> without extension. Valid categories: constellations, stars, messier, planets. Suggest a name based on the subject (e.g. messier/hubble_m42).
3. Crop (optional) — x1,y1,x2,y2 to extract a sub-region before resizing. Skip if the subject is already well-centred and the image is in portrait or square orientation.

Validate before proceeding — reject and ask again if any check fails:

• Category: must be exactly one of constellations, stars, messier, planets.
• Name (filename part): must match [a-z0-9_]+ only.
• Crop: if provided, must be exactly four tokens that are each non-negative integers.
• URLs: must begin with https://. Reject http://, file://, and all other schemes. Also reject any URL whose hostname resolves to a private/loopback range — this is enforced again at download time (Step 2), but reject obviously bad hostnames early (e.g. localhost, 127.*, 10.*, 192.168.*, 169.254.*, [::1]).
• Local paths: must match [a-zA-Z0-9/_.\- ]+ — reject any path containing shell metacharacters (", ', `, $, !, &, |, ;, (, ), <, >, \n, etc.). If the user provides such a path, ask them to move or rename the file.

Step 2 — Write inputs to a config file (IMPORTANT — security boundary)

Never interpolate user-provided values into shell command strings. Instead, use the Write tool to write a JSON config file. Python will read from it — the values never pass through the shell.

Use the Write tool to create /tmp/celestial_cfg.json with the following structure (substituting the actual validated values you collected):

{
  "source": "/validated/local/path/or/https://validated.url/image.jpg",
  "category": "messier",
  "name": "hubble_m42",
  "crop": [x1, y1, x2, y2]
}

Set "crop" to null if no crop was requested.

Step 3 — Acquire the image

If the source is a URL, download it using the script below. All inputs are read from the config file — no user data ever appears in a shell command line.

python3 - <<'EOF'
import json, os, socket, tempfile, urllib.parse, urllib.request
import ipaddress

with open('/tmp/celestial_cfg.json') as f:
    cfg = json.load(f)

url = cfg['source']

# Validate scheme (defence-in-depth; Step 1 already checked this)
parsed = urllib.parse.urlparse(url)
if parsed.scheme != 'https':
    raise SystemExit(f'rejected scheme: {parsed.scheme!r}')

# Resolve hostname and block private/loopback ranges (SSRF guard)
host = parsed.hostname
try:
    addr = ipaddress.ip_address(socket.getaddrinfo(host, None)[0][4][0])
except Exception as e:
    raise SystemExit(f'cannot resolve host {host!r}: {e}')
if addr.is_private or addr.is_loopback or addr.is_link_local or addr.is_reserved:
    raise SystemExit(f'rejected private/reserved address: {addr}')

# Derive a safe extension from the URL path (ignore query strings)
url_path = parsed.path
suffix = os.path.splitext(url_path)[1][:5].lower() or '.jpg'
allowed_exts = {'.jpg', '.jpeg', '.png', '.webp', '.tif', '.tiff'}
if suffix not in allowed_exts:
    suffix = '.jpg'

# Use a unique temp file to avoid race conditions
fd, src_path = tempfile.mkstemp(suffix=suffix, prefix='celestial_src_')
os.close(fd)

urllib.request.urlretrieve(url, src_path)
print('downloaded to', src_path, os.path.getsize(src_path), 'bytes')

# Store the resolved local path back into config for subsequent steps
cfg['resolved_src'] = src_path
with open('/tmp/celestial_cfg.json', 'w') as f:
    json.dump(cfg, f)
EOF

If the source is already a local path, add "resolved_src" to the config manually using the Write tool (copy the existing config and add "resolved_src": "<the local path>").

Read the source image file with the Read tool to view it visually.

Step 4 — Inspect dimensions

All inputs come from the config file — nothing is passed via shell arguments.

python3 - <<'EOF'
import json, os
from PIL import Image

with open('/tmp/celestial_cfg.json') as f:
    cfg = json.load(f)

src = cfg['resolved_src']
img = Image.open(src)
print('size:', img.size, '  mode:', img.mode)
print('file size:', os.path.getsize(src), 'bytes')
EOF

Report dimensions to the user. If the aspect ratio is very different from 480:800 (3:5) and no crop was specified, suggest a crop that captures the most interesting region and ask the user to confirm before proceeding. If the user provides a new crop, update /tmp/celestial_cfg.json using the Write tool.

Step 5 — Convert to 480×800 WebP

All inputs come from the config file. Crop values are parsed as integers with bounds checks.

python3 - <<'EOF'
import json, os, tempfile
from PIL import Image

with open('/tmp/celestial_cfg.json') as f:
    cfg = json.load(f)

src  = cfg['resolved_src']
crop = cfg.get('crop')  # null or [x1, y1, x2, y2]

if crop is not None:
    if len(crop) != 4 or not all(isinstance(v, int) and v >= 0 for v in crop):
        raise SystemExit('crop must be a list of 4 non-negative integers')
    crop = tuple(crop)

img = Image.open(src).convert('RGB')

if crop:
    img = img.crop(crop)

target_w, target_h = 480, 800
src_w, src_h = img.size
scale = max(target_w / src_w, target_h / src_h)
new_w = round(src_w * scale)
new_h = round(src_h * scale)
img = img.resize((new_w, new_h), Image.Resampling.LANCZOS)

left = (new_w - target_w) // 2
top  = (new_h - target_h) // 2
img = img.crop((left, top, left + target_w, top + target_h))

fd, out_path = tempfile.mkstemp(suffix='.webp', prefix='celestial_out_')
os.close(fd)
img.save(out_path, 'WEBP', quality=80, method=6)
print('saved', out_path, os.path.getsize(out_path), 'bytes')

cfg['out_path'] = out_path
with open('/tmp/celestial_cfg.json', 'w') as f:
    json.dump(cfg, f)
EOF

Read the output .webp file (path printed above) to visually verify quality and framing. If it looks poor (badly cropped, blurry, or key detail lost), update the crop field in /tmp/celestial_cfg.json using the Write tool and repeat this step.

Format selection rationale

WebP lossy quality=80 is almost always the smallest option for photographic images and is universally supported on Android 4.0+. Only fall back to JPEG if WebP produces a larger file (rare). Never use PNG for photographic images.

Step 6 — Check file size

Typical range for existing assets is 10–90 KB. If the output exceeds 150 KB, try quality=70:

python3 - <<'EOF'
import json, os
from PIL import Image

with open('/tmp/celestial_cfg.json') as f:
    cfg = json.load(f)

out = cfg['out_path']
img = Image.open(out)
img.save(out, 'WEBP', quality=70, method=6)
print(os.path.getsize(out), 'bytes')
EOF

Step 7 — Deploy

All values come from the config file. Category and name are re-validated here, and the resolved destination path is checked to be inside the assets directory before any copy occurs.

python3 - <<'EOF'
import json, os, re, shutil

with open('/tmp/celestial_cfg.json') as f:
    cfg = json.load(f)

category = cfg['category']
name     = cfg['name']
out      = cfg['out_path']

VALID_CATEGORIES = {'constellations', 'stars', 'messier', 'planets'}
if category not in VALID_CATEGORIES:
    raise SystemExit(f'invalid category: {category!r}')
if not re.fullmatch(r'[a-z0-9_]+', name):
    raise SystemExit(f'invalid name: {name!r}')

assets_root = os.path.abspath('app/src/main/assets/celestial_images')
dest = os.path.abspath(os.path.join(assets_root, category, f'{name}.webp'))

if not dest.startswith(assets_root + os.sep):
    raise SystemExit('path traversal detected — aborting')

os.makedirs(os.path.dirname(dest), exist_ok=True)
shutil.copy2(out, dest)
print('deployed to', dest)
EOF

Then update object_info.json to refer to the new image.

Step 8 — Report

Tell the user:

• Saved to: app/src/main/assets/celestial_images/<category>/<name>.webp
• File size: X KB
• Dimensions: 480 × 800
• imageKey to use in object_info.json: "<category>/<name>.webp"
• imageCredit: remind the user to add an appropriate credit string (e.g. "NASA/ESA/Hubble")
• Suggest git staging: git add app/src/main/assets/celestial_images/<category>/<name>.webp

Reference — existing naming conventions

| Category | Prefix examples | |---|---| | messier/ | hubble_m1, hubble_m42, eso_m104 | | stars/ | eso_sirius, nasa_sun, hubble_eta_carinae | | constellations/ | iau_orion, iau_ursa_major | | planets/ | hubble_saturn, nasa_mercury |

Use <source_agency>_<subject> in lowercase with underscores.

Troubleshooting

• Pillow not installed: pip install Pillow
• WebP larger than JPEG: use JPEG quality=85 instead (uncommon for space photos)
• URL download fails: ask the user to download the image manually and provide a local path
• Image too dark/washed out after resize: the source may need colour correction — note it in the report but do not auto-correct