[muglo] Re: Editing and converting Images (Was: PowerPoint
- From: Eric Dunbar <eric.dunbar@xxxxxxxxx>
- To: muglo@xxxxxxxxxxxxx
- Date: Thu, 27 Jan 2005 12:00:33 -0500
On Wed, 26 Jan 2005 15:49:22 -0500, Lee Dickey <Lee@xxxxxxxxx> wrote:
> On 2005 Jan 24, at 09:11, Garth Phillips wrote:
>
> > When pulling pix in or out of power point try saving the image in the
> > bitmap
> > rather than jpg format.... While you can't manipulate them as much
> > afterwards, bmp files are usually 1/3 the size of jpg. In doing this,
> > I've
> > taken presentations from 20MB down to 2 or 3MB. Loads and mails lots
> > faster
> > too!
The format use when you EXPORT the image from PP will not change the
quality contained in the original file. It's best to export the image
into the same format as was used to insert it (i.e. JPEG for JPEGs,
BMP for BMPs, etc.).
> Garth's comment about size and manipulability
> does not match my experience. Through experimentation,
> I have found that a lot depends on the type
> of picture.
<snip Very detailed and correct summary of image compression>
There is a slight hitch in PowerPoint and that is that (the Windows
version at least) sometimes compresses BMP files. JPEGs come in as
compressed images and PowerPoint seems not to be able to handle them
effectively -- if you manipulate them they baloon in size. The few
times I used BMPs I managed to retain the high quality of uncompressed
images but with "smaller" .ppt files (I wonder if it runs BMPs through
a GIF-style compression).
Just as a Cole's Notes version of image formats:
You've got (1) uncompressed, (2) lossy compression and (3) lossless
compression. GIF and compressed TIFF are loss-less compression
techniques. You don't lose detail but it also doesn't make for very
small files. JPEG is by far the most famous lossy compression -- you
can determine how much detail you are willing to lose, and, thereby
create rather small images. Uncompressed images... well, they're huge.
The major reason you'd work with uncompressed images is for
manipulation speed (in PhotoShop, for e.g.) -- compressed images (even
loss-less) take time to decompress. With 2.5 GHz G5 CPUs this is no
longer an issue for most tasks, but when we were still living with 100
MHz 601s it was more efficient (sometimes) for PhotoShop & the likes
to read uncompressed images from disk than to waste CPU cycles
decompressing TIFFs or JPEGs.
JPEG is a "lossy" compression.
GIF is a "loss less" compression.
BMP is uncompressed which means its colour (8, 16, 24, 32 bit per
pixel) images are *huge*.
TIFF has a variety of states, but, when compressed it's compressed
using lossless compression -- you can get uncompressed images which
are downright huge but you can also apply different styles of
compression to bring file sizes down like GIF (TIFF is BMP and GIF
combined into one format).
Eric.
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