I don't know of any reference materials, so here goes.
apply to
Selected Pictures
All pictures in document
These options do just what they say -- select "selected pictures" to apply
compression to the picture you have selected. Select "all pictures in
document" to apply the compression settings to every image in the document.
change resolution
web/screen (96 dpi)
print (200 dpi)
no change
These options are the actual compression. Choose Web/Screen if you want the
image(s) compressed to 96 dots per inch (it's actually PPI, pixels per inch,
but it's labeled as DPI probably because more people know what that is).
Choose Print if you don't want the picture(s) compressed that much -- it
will compress to 200 ppi instead of 96. Select No Change if you don't want
the picture(s) to be compressed. Basically follow the settings -- if you're
going to just show the file on a monitor or projector and print handouts,
choose Web/Screen. If you need to do higher-end printing (which some people
use PPT for), then you'll want to choose Print.
Here's more explanation of PowerPoint and resolution:
Scanning - Bitmap Resolution - DPI
http://www.pptfaq.com/FAQ00074.htm
As an example, if you've taken high-res images on a digital camera and then
inserted them into PPT, they'll generally be very oversized for what you
need for a presentation. Generally speaking, your PPT images need to be only
1024 x 768 pixels -- or whatever settings your monitor is set to, because
PPT can't show any more than your monitor can. But on newer mega-pixel
cameras, you get, well, mega amounts of pixels! So your inserted images will
have tons of extra pixels. This causes the file size to be
disproportionately big. I'll give you a specific example. I had a client try
to send me a file recently. She'd added a bunch of high-res pictures to her
250-slide presentation, and the file size was 500 MB. That's half a gig!! I
had her run picture compression, and the file became about 50MB.
Now, one of the images on a slide took up about 1/4 of the slide. So when
she ran compression, it compressed that image to about 2.5 inches x 2 inches
(about 1/4 of the slide) at 96 dpi. When I decided to make the picture fill
the slide, it became very pixelated. I needed more pixels. Luckily the
client had sent me the original file on CD, so I was able to go back to the
large original picture with extra pixels. I inserted that into the
presentation, made it full-slide size, then compressed it. So then it
compressed to 10 inches x 7.5 inches at 96 dpi and was no longer pixelated.
My point is, you want to think about the size of the picture on the slide
before you go compressing. If you think you might want the picture to be
much bigger, then don't compress it. I think you can choose "apply to
selected picture" and then "no change" to prevent that image from being
compressed, but now that I think of it, I'm not positive it works that way.
I know the RnR Image Optimizer compression utility does work that way,
though.
http://www.pptools.com/index.html Hopefully someone will be along
shortly to clarify about PPT's picture compression.
Options
Compress pictures
Delete cropped areas of pictures
Compress pictures is obvious. Choose it if you want to compress pictures --
that is, change the DPI/PPI as described above.
Delete cropped areas. When you crop a picture in PPT, those parts of the
picture are still there. To see it in action, insert a picture, then crop
it. Then drag the cropmark the opposite direction. The cropped information
is still there. If you choose this option, then those parts will be deleted.
This makes the file size a bit smaller, usually, because unnecessary parts
that weren't showing are now actually deleted from the file.
