PngConform: A Comprehensive PNG Validator in Ruby

$ png_conform check -v image.png
📄 image.png (32768 bytes)

  ✓ 📦 IHDR at 0x0000c (13 bytes)
  ✓ 📦 gAMA at 0x00025 (4 bytes)
  ✓ 📦 cHRM at 0x00035 (32 bytes)
  ✓ 📦 IDAT at 0x00061 (65445 bytes)
  ✓ 📦 IEND at 0x10072 (0 bytes)

✓ No errors detected in image.png (5 chunks)

$ png_conform check -v corrupted.png
📄 corrupted.png (1024 bytes)

  ✗ 📦 IHDR at 0x0000c (13 bytes)
  ✓ 📦 PLTE at 0x00025 (12 bytes)
  ✗ 📦 IDAT at 0x00035 (891 bytes)
  ✓ 📦 IEND at 0x003ec (0 bytes)

VALIDATION ERRORS:
  ❌ ERROR: IHDR: invalid bit depth 3 for color type 2
  ❌ ERROR: CRC error in chunk IDAT (expected 0x12345678, got 0x87654321)
  ⚠️  WARNING: Missing recommended chunk gAMA

❌ 2 errors, 1 warning in corrupted.png (4 chunks)

$ png_conform check --format yaml image.png
---
filename: "./spec/fixtures/pngsuite/background/bgwn6a08.png"
file_type: PNG
file_size: 202
compression_ratio: -97.3
crc_errors_count: 0
valid: true
image:
  width: 32
  height: 32
  bit_depth: 8
  color_type: 6
  color_type_name: RGBA
  interlaced: false
chunks:
  total: 5
  types:
  - IDAT
  - IEND
  - IHDR
  - bKGD
  - gAMA
resolution:
  dimensions: 32x32
  megapixels: 0.0
  dpi:
  retina:
    at_1x: 14.1x14.1pt
    at_2x: 7.1x7.1pt
    at_3x: 4.7x4.7pt
    recommended: "@1x (too small for higher densities)"
    ios:
    - Custom size
    android: ldpi or mdpi
recommendations:
- Image is too small for Retina displays - consider @2x/@3x versions
- Add pHYs chunk with DPI information for print compatibility

$ png_conform check --format json image.png
{
  "filename": "image.png",
  "file_type": "PNG",
  "file_size": 32768,
  "crc_errors_count": 0,
  "compression_ratio": -89.2
}

$ png_conform check --format yaml corrupted.png
---
filename: corrupted.png
file_type: PNG
file_size: 1024
crc_errors_count: 1
valid: false
errors:
- severity: error
  message: 'IHDR: invalid bit depth 3 for color type 2'
  chunk_type: IHDR
- severity: error
  message: 'CRC error in chunk IDAT'
  chunk_type: IDAT
  expected: '0x12345678'
  actual: '0x87654321'
- severity: warning
  message: Missing recommended chunk gAMA

$ png_conform check --format json corrupted.png
{
  "filename": "corrupted.png",
  "file_type": "PNG",
  "file_size": 1024,
  "crc_errors_count": 1,
  "valid": false,
  "errors": [
    {
      "severity": "error",
      "message": "IHDR: invalid bit depth 3 for color type 2",
      "chunk_type": "IHDR"
    },
    {
      "severity": "error",
      "message": "CRC error in chunk IDAT",
      "chunk_type": "IDAT",
      "expected": "0x12345678",
      "actual": "0x87654321"
    },
    {
      "severity": "warning",
      "message": "Missing recommended chunk gAMA"
    }
  ]
}

$ png_conform check --no-color image.png
OK: image.png (800x600, 8-bit/color RGB, non-interlaced)

$ png_conform check -p indexed.png
OK: indexed.png (32x32, 2-bit palette, non-interlaced)
  chunk IHDR at offset 0x0000c, length 13
  chunk PLTE at offset 0x00025, length 12
    0:  (255,255,255) = gray100
    1:  (204,204,204) = gray80
    2:  (153,153,153) = gray60
    3:  (102,102,102) = gray40
  chunk IDAT at offset 0x0003d, length 147
  chunk IEND at offset 0x000d4, length 0

$ png_conform check --profile web image.png
WARN: image.png: missing required chunk gAMA (web profile)
WARN: image.png: missing required chunk sRGB (web profile)
OK: image.png (800x600, 8-bit/color RGB, non-interlaced)

$ png_conform check icon.png
✅ OK: icon.png, (PNG, 202 bytes, 5 chunks, 🗜️ -97.3%)

RESOLUTION ANALYSIS:
  Dimensions: 32x32 (0.0 megapixels)
  DPI: Not specified

  Retina Analysis:
    @1x: 14.1x14.1pt (Small icon)
    @2x: 7.1x7.1pt (Small icon)
    @3x: 4.7x4.7pt (Small icon)
    Recommended: @1x (too small for higher densities)
    iOS: Custom size
    Android: ldpi or mdpi

  Recommendations:
    [HIGH] Image is too small for Retina displays - consider @2x/@3x versions
    [MEDIUM] Add pHYs chunk with DPI information for print compatibility

$ png_conform check --optimize large-photo.png
✅ OK: large-photo.png, (PNG, 4.5 MB, 8 chunks, 🗜️ -42.1%)

OPTIMIZATION SUGGESTIONS:
  1. [HIGH] Convert from 16-bit to 8-bit depth (saves ~45% = 2.1MB)
  2. [MEDIUM] Remove 3 unnecessary chunks (tIME, pHYs, oFFs) (saves 156 bytes)
  3. [LOW] Remove interlacing for smaller file size (saves ~15% = 680KB)

  Total Potential Savings: 2.8MB (62.2%)

$ png_conform check --mobile-ready app-icon@2x.png
✅ OK: app-icon@2x.png, (PNG, 2.3 KB, 5 chunks, 🗜️ -88.5%)

MOBILE & RETINA READINESS:
  Status: ✓ READY

  Checks:
    Retina Ready: ✓
    Mobile Friendly: ✓
    Web Suitable: ✓

  Retina Densities:
    @1x: 44.0x44.0pt
    @2x: 22.0x22.0pt
    @3x: 14.7x14.7pt
    Recommended: @2x

  Screen Coverage:
    Mobile (375x667): 23.5% x 13.2%
    Desktop (1920x1080): 4.6% x 8.1%

  Load Time: 25ms (fast)