Halo effect when resizing images with alpha transparency

[XnTriq]

• <--// Moderator's note: This topic has been split off from “Reducing Halo Effect in Rescaled/Resized Images” (XnConvert). //-->

Download logo.png…

Original: Remove alpha channel + Show Mask + Use alpha channel + Resized (no “halo”)

p116715_1.png (23.79 KiB) Viewed 546 times

… and run it through PngOptimizer to eliminate the so-called “dirty transparency”.

Optimized: Remove alpha channel + Show Mask + Use alpha channel + Resized (“halo”)

p116715_2.png (27.23 KiB) Viewed 546 times

The challenge is to produce the same result when resizing the original and the optimized logo.

More samples and screenshots illustrating “dirty transparency”:

• Re: PNG with transparency not showing
• Re: Transparency & alpha
• Transparency

[XnTriq]

The challenge is to produce the same result when resizing the original and the optimized logo.

Pixlr Editor passes the test with flying colors.

Resizing (25%) mouth1.png with XnView v2.13 (Lanczos) vs. Pixlr Editor:

p117075.gif (9.13 KiB) Viewed 531 times

There's a tutorial by Jason Summers explaining how to fix this issue:

• ImageWorsener
  • Resizing images with transparency
  • “Clamping” intermediate samples » Clamping and transparency