PNGs don't compress well

[Craig]

I do work for an organization whose members make extensive use of PNGs
provided by the company in their PowerPoint presentations. The images are
excellent quality, but not really PowerPoint friendly right off the CD. They
are often 10+ MB. Using the Compress Pictures command reduces their size
minimally (e.g. a 13MB image reduced to 12MB). I can easily resave the image
as a jpeg and reinsert it and it is a manageable size. I am jsut curious as
to why the PNGs don't compress well. Is it just a characteristic of PNGs or
of the compression engine in PowerPoint?
The presentations run fine on our systems (XP Pro, Office 2003), but I need
to archive them to a CD and website after each seminar and must keep the
file sizes reasonable (I aim for less than 3MB per presentation).
Any information would be appreciated.

 

[Steve Rindsberg]

I do work for an organization whose members make extensive use of PNGs
provided by the company in their PowerPoint presentations. The images are
excellent quality, but not really PowerPoint friendly right off the CD. They
are often 10+ MB. Using the Compress Pictures command reduces their size
minimally (e.g. a 13MB image reduced to 12MB). I can easily resave the image
as a jpeg and reinsert it and it is a manageable size. I am jsut curious as
to why the PNGs don't compress well. Is it just a characteristic of PNGs or
of the compression engine in PowerPoint?
The presentations run fine on our systems (XP Pro, Office 2003), but I need
to archive them to a CD and website after each seminar and must keep the
file sizes reasonable (I aim for less than 3MB per presentation).
Any information would be appreciated.

How do you insert the PNGs to begin with?
That may have an effect on how they compress.

What compression settings have you chosen?

Have you tried any of the commercially available compression tools?
Our Optimizer is one: http://optimizer.pptools.com
There are others; ours and most of the others allow you to try them out before
purchasing.

But first, let's look at how you're creating the presentations in the first place.
Maybe there's a way to get you some decent compression w/o an external tool