imagemagick resizing and quality PNG

Question

In my application I need to resize and make the quality on PNG files poorer.

In full size the PNGs are 3100x4400px using 2,20MB disk space.

When running the following command:

convert -resize 1400 -quality 10 input.png output.png 

the images are resized to 1400x2000 using 5,33MB disk space.

So my question is: How can I reduce the file size?

Answer 1

1. You can further reduce quality of PNG by using posterization:

   https://github.com/pornel/mediancut-posterizer (Mac GUI)

   This is a lossy operation that allows zlib to compress better.

2. Convert image to PNG8 using pngquant.

   It reduces images to 256 colors, so quality depends on the type of image, but pngquant makes very good palettes, so you might be surprised how often it works.

3. Use Zopfli-png or AdvPNG to re-compress images better.

   This is lossless and recommended for all images if you have CPU cycles to spare.