title: Why does 1bpp PNG image file size increase when the colors are inverted?
body: <p>When I generate black-and-white png images with 1 bit per pixel indexed color, it seems to make a noticeable difference in the file size if if I choose to use black background over white one. The attached images should have exactly the same information, and both are created by .NET 4's Bitmap.Save() function.</p>
  <p>Why is the image with white background significantly larger when compressed?</p>
  <p>Black background: 4.62KB
  <a href="https://www.dropbox.com/s/t8v2ovhobgkgtph/output.png?dl=0" rel="nofollow noreferrer">Black background 4.62KB</a></p>
  <p>White background: 5.67KB
  <a href="https://www.dropbox.com/s/ymszu5g2y9r6a2s/output2.png?dl=0" rel="nofollow noreferrer">White background: 5.67KB</a></p>