PNG's or JPEG's ~ What's best to run in Power Point?

[Guest]

I have a PPP that has many images in the 2500 x 1900 pixels, all JPEG’s that
are running at 800 x 600 VGA settings. After reading a tutorial I have
learned at these setting the images are highly compressed. I also read that I
should resize the images to 800 x 600 and save them as PNG’s if I am running
VGA settings.

I took one group of photos that were the large images as JPEG’s that
contained 33 Megs as a group. These same photos resized to 800 x 600 now are
20 Meg’s saved as PNG’s as a group.

Now if I resize the JPEG’s to 800 x 600 and resave them as JPEG’s the group
file size is only 4.3 megs. I understand ever time a JPEG is save quality is
lost.

Question: Will the images that are saved as a PNG at 800 x 600 load faster
in Power Point even though the file size is larger than the JPEG’s 800 x 600?
I have to distribute the PPP so that it runs from a autorun CD using 2003 PP
Viewer.

 

[Bill Dilworth]

JPG's are compressed and interpreted image files. This means that the JPG
file algorism looks at the colors and say the first 25 pixels are all ABOUT
the same color so I'll same that as 25 of the SAME color. This allows for a
high compression ratio. Each time a file is saved, this algorism runs this
interpretation may degrade the image quality (similar to a Xerox copy of a
copy of a copy etc.)

PNG files are compressed, but not interpreted. So the PNG algorism says the
first 16 are the SAME so I'll store that as 16 of color A, then 2 of color
B, then 7 of color A. A lower compression, but no image quality loss. PNG
files are also able to use a transparent setting.

The file loading speed has to do with the file size, so the JPG files will
load faster. If the image quality is acceptable, then you will be better
off with the JPGs, however, if the quality of the image is more important or
a transparency is needed, you will be better off with a PNG.

Hope this helps,
Bill Dilworth
Microsoft PPT MVP Team
Users helping fellow users.
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[Steve Rindsberg]

Now if I resize the JPEG’s to 800 x 600 and resave them as JPEG’s the group
file size is only 4.3 megs. I understand ever time a JPEG is save quality is
lost.

That's true; what I'd do is convert your high resolution JPGs to PNGs and hang
onto those as your "master" images. Then as you need other sizes, resample down
and save to new files as either JPG or PNG (look at them onscreen in your PPT
show; your eyes will tell you whether the JPGs have suffered from too much
compression or not; if they look nasty, use the PNGs.)

Question: Will the images that are saved as a PNG at 800 x 600 load faster
in Power Point even though the file size is larger than the JPEG’s 800 x 600?
I have to distribute the PPP so that it runs from a autorun CD using 2003 PP
Viewer.

It'd be a good idea to perform some tests on typical equipment you're targeting,
but here's my guess:

The presentation itself will load more slowly as PNG, since there'll be more data
to read off the CD. Individual slides may advance a bit more slowly with the
images saved as JPG, since PPT has to decompress them for playback. In general,
given the speed of modern PCs (actually of PCs since the 386 or so) it's faster to
get a given amount of data into memory by taking less off the disk and expanding
it into more in memory than it is to read more data, already uncompressed, off the
drive or network.

Or in plain English, I'm betting on JPGs being a bit faster.