Photoshop: Why does LZW compression in TIFF sometimes increase file size?

  • 1
  • Question
  • Updated 4 years ago
  • Answered
  • (Edited)
Scenario:
Adobe PhotoShop 5.1 Version:
12.1 (12.1x20110328 [20110328.r.145 2011/03/28:10:30:00 cutoff; r branch]) x64
Operating System: Mac OS 10.7.2

Problem:
When storing a TIFF image using the LZW compression, the file size consistently increases by some 20-30%! I'm using TIFF mode RRG 16 bit. I thought the resulting file-size was supposed to decrease when using this option?. Storing it once more w/ None compression will again reduce the file size to the smaller original state.

Any ideas why this happens?
Photo of Erik Aaseth

Erik Aaseth

  • 4 Posts
  • 0 Reply Likes

Posted 4 years ago

  • 1
Photo of Chris Cox

Chris Cox, Sr. Computer Scientist

  • 20280 Posts
  • 674 Reply Likes
Official Response
Yes, LZW is not very good with noisy data, and 16 and 32 bit data looks a lot like noise to the LZW algorithm.

That's not a bug, just the way LZW works.

For 16 and 32 bit data, ZIP/Flate compression usually works better.
But not all TIFF readers understand ZIP/Flate compression, so it's still optional.