I recently read jrista's marvellous q&a from photo.stackexchange.

While the question is titled "How do I generate high quality prints with an ink jet printer?" it covers DPI & PPI relationship to quite an extent and has real-world print examples.

Current Q&A contents:

• Summary
• Detailed Explanation
• Empirical Studies:
  • Does PPI really matter?
  • Extreme digital upscaling

I recently read jrista's marvellous q&a from photo.stackexchange.

While the question is titled "How do I generate high quality prints with an ink jet printer?" it covers DPI & PPI relationship to quite an extent and has real-world print examples.

Current Q&A contents:

• Summary
• Detailed Explanation
• Empirical Studies:
  • Does PPI really matter?
  • Extreme digital upscaling