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ImageResolutionChecker

A Swift command-line tool that fetches a random image from a specified Digital NZ collection and checks the actual pixel dimensions of available image URLs.

What it does

  1. Requests a random image from the specified collection via Digital NZ API
  2. Downloads image data from available URLs (large_thumbnail_url and object_url)
  3. Extracts pixel dimensions using ImageIO
  4. Outputs machine-parseable JSON with resolution data

Usage

Using the wrapper script (recommended):

# Check a specific collection
DIGITALNZ_API_KEY=your_key ./test-image-resolution.sh "Te Papa Collections Online"

# Or with export
export DIGITALNZ_API_KEY=your_key
./test-image-resolution.sh "Auckland Museum Collections"

Or call the binary directly:

# Check a specific collection
DIGITALNZ_API_KEY=your_key .build/debug/ImageResolutionChecker "Canterbury Museum"

Output Format

Machine-parseable JSON with image resolution data:

{
  "collection" : "Alexander Turnbull Library Flickr",
  "largeThumbnailUrl" : {
    "resolution" : {
      "height" : 639,
      "width" : 465
    },
    "url" : "https://live.staticflickr.com/5693/21448090258_583b745001_z.jpg"
  },
  "objectUrl" : {
    "resolution" : {
      "height" : 5155,
      "width" : 3748
    },
    "url" : "https://live.staticflickr.com/5693/21448090258_f6edccff24_o.jpg"
  },
  "recordId" : 36372943,
  "title" : "Soldiers loading a New Zealand trench mortar, near Colincamps, France"
}

Note: Not all collections provide both URL types. Some may only have large_thumbnail_url, and object_url may be omitted from the output if not available.

Use Cases

  • Verify image quality - Check if a collection provides high-resolution images
  • Compare URL fields - See the difference between large_thumbnail_url and object_url resolutions
  • Collection evaluation - Determine if a collection is suitable for high-quality image display
  • Automation - Build scripts to evaluate multiple collections systematically

Example Usage in Scripts

# Test multiple collections and save results
for collection in "Te Papa Collections Online" "Auckland Museum Collections" "Canterbury Museum"; do
  echo "Testing: $collection"
  DIGITALNZ_API_KEY=$API_KEY ./test-image-resolution.sh "$collection" >> results.jsonl
done

# Check if large_thumbnail_url has acceptable resolution
DIGITALNZ_API_KEY=$API_KEY ./test-image-resolution.sh "Te Papa Collections Online" | \
  jq '.largeThumbnailUrl.resolution | .width >= 1000 and .height >= 1000'

# Extract just the resolution dimensions
DIGITALNZ_API_KEY=$API_KEY ./test-image-resolution.sh "Canterbury Museum" | \
  jq '{collection, large: .largeThumbnailUrl.resolution, object: .objectUrl.resolution}'

Understanding the Results

large_thumbnail_url

This field typically contains a medium-to-large preview image. Resolution varies by collection:

  • Some collections: 300-800 pixels
  • Others: 1000+ pixels

object_url

When present, this often provides the highest resolution available:

  • Flickr collections: Full resolution (often 3000+ pixels)
  • Other collections: May be similar to large_thumbnail_url or not provided

Collection-Specific Behavior

Different collections have different URL processing:

  • Flickr-based (e.g., Alexander Turnbull Library): object_url provides full resolution
  • Recollect-based (e.g., Wellington City): URLs require processing for full resolution
  • Museum collections: Vary widely in available resolutions

Features

  • Automatic build before execution
  • Fetches random images for representative sampling
  • Clean error messages for missing API key or invalid collections
  • JSON output for easy parsing and automation
  • Handles missing URL fields gracefully