Question on Compress Pictures: Will multiple uses degrade images?

[Colin Higbie]

If I repeatedly use the Format picture option to Compress Pictures, Select
either Web/Screen or Print, and check the "Compress Pictures" box, will the
quality of the pictures keep being degraded each time, or once they are
compressed, does it know that and not try to recompress them?

I know this would not be an issue if they were being compressed in a
lossless format, but I've inserted them as high resolution JPEG's (too high
to leave them that way). That's a lossy compression method, so if PowerPoint
turns it into a bitmap, with the JPEG smudges, then recompresses it, those
distortions/smudges will be amplified each time.

How does PowerPoint handle its internal compression? What method dooes it
use? Will it degrade my images if I recompress all every time I add a few
new pictures?

Is it a mistake to put my pictures in as hi-res JPEG's? Do I need to
compress them down to the desired size first? I guess if PowerPoint is using
something like ZIP to compress, it won't get as good a compression result as
if I did them all manually ahead of time. I'm really just hoping to save
myself all that work.

Thanks for any insight,
Colin

 

[Steve Rindsberg]

If I repeatedly use the Format picture option to Compress Pictures, Select
either Web/Screen or Print, and check the "Compress Pictures" box, will the
quality of the pictures keep being degraded each time, or once they are
compressed, does it know that and not try to recompress them?

I don't know offhand, but you could compress once, note the file size of the
PPT then compress again a time or two and see if it changes.

I'd also test it by compressing to the medium level then again to the highest
compression level.

How does PowerPoint handle its internal compression? What method dooes it
use? Will it degrade my images if I recompress all every time I add a few
new pictures?

This isn't documented anywhere I know of. A few tests, especially of images
like screenshots, will give you a good idea quickly enough.

Is it a mistake to put my pictures in as hi-res JPEG's? Do I need to
compress them down to the desired size first?

It'd be better to include images that are no bigger than they need to be, say
1024x768 if you plan to use the pres. as a screen show.

You might also want to look at our commercial PPTools Optimizer at the PPTools
url below. It will very definitely not re-compress an image once it's touched
it.

--
Steve Rindsberg, PPT MVP
PPT FAQ: www.pptfaq.com
PPTools: www.pptools.com
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[TAJ Simmons]

Colin,

What Steve said....but also...
Why are my PowerPoint files so big? What can I do about it?
http://www.rdpslides.com/pptfaq/FAQ00062.htm

Is it a mistake to put my pictures in as hi-res JPEG's? Do I need to

compress them down to the desired size first? I guess if PowerPoint is using
something like ZIP to compress, it won't get as good a compression result as
if I did them all manually ahead of time.

If it was me I'd make sure they had the correct amount of PIXELS in the first place.

Cheers
TAJ Simmons
microsoft powerpoint mvp

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