Legacy ImageMagick Discussions Archive

Hello all,

I am new to imagemagick and have a question or two. I'd really appreciate if anyone could lend some advice...

I have imagemagick on my server, I do not know if it is Q8 or Q16 - I only heard about these today, as far as i was aware it was just imagemagick.

I am trying to compress some png images so they save as png-8 (not png 24, I want smaller more compressed files). I was advised by someone that I may need to install imagemagick Q8 instead of Q16. Would that be correct advise, would it mean images made as a result of imagemagick Q8 were smaller file size (and less quality)?

Also if I wanted to install imagemagick q8, how would I go about that. I have a FreeBSD server...

Thanks for any help, as I said it's really appreciated as this is really quite lost on me.

You do not need to install Q8, the default Q16 will work fine.

You can find out what version of IM by typing

convert -version

and the reply will be something like

Version: ImageMagick 6.7.8-2 2012-07-08 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2012 ImageMagick Studio LLC
Features:

To compress your png, do the following:
(this assumes your png has no transparency. if so then if it is 8-bit transparency, converting palette via PNG8: will make the transparency binary)

convert image.png -depth 8 PNG8:result.png

If this does not work, try either

convert image.png -depth 8 -type palette PNG8:result.png
or
convert image.png -depth 8 -type palette result.png

If transparency in your image, then use -type palettematte.

see
http://www.imagemagick.org/script/comma ... .php#depth
http://www.imagemagick.org/Usage/formats/#png
http://www.imagemagick.org/Usage/formats/#png_formats

You can just do You don't actually need either -type or -depth; the PNG8 sub-format sets those for you.
You might want to strip out unnecessary ancillary PNG chunks, which the "-strip" option will do for you: fmw42 is correct, you can use either Q8 or Q16 for this.

Thanks guys, some of this really helped