png2ico exporting ICO in lower quality than the original PNGs

Question

I have 6 PNG files that I want to bundle into one ICO file. I'd like to use something like png2ico instead of a web app like ConvertICO.org's web app.

When the ICO is produced using png2ico, the quality of the ICO seems to have dropped. Below are 2 images (100% view and zoomed in) comparing the png2ico output (right) to the original PNG (left).

Is this a limitation of png2ico? Can I stop png2ico from lowering the quality? Can you recommend another way of bundling 6 PNGs into 1 ICO using Terminal on OSX?

Answer 1

I emailed the developer of png2ico and it sounds like png2ico only supports 256 colors which isn't acceptable for what I needed. I have since discovered that ImageMagick can convert and bundle multiple PNGs into one ICO thanks to Rob W's post here.