[thelist] compression / uncompression
Lee Kowalkowski
lee.kowalkowski at googlemail.com
Fri Jan 18 10:03:59 CST 2008
On 18/01/2008, Jason Handby <jason.handby at corestar.co.uk> wrote:
> Image file formats like JPEG use "lossy" compression; if you "compress"
> an image by saving it out as a JPEG then yes, data is lost in the
> process.
>
> In programs like Photoshop you can choose the quality setting when you
> save an image as a JPEG, and this determines how much data gets thrown
> away and how big the resulting JPEG file is.
Well, JPEGs always lose data, they approximate the image a bit like
you could a do 'line of best fit' on a plotted graph using a Bézier
curve. The quality setting for JPEG just does a more detailed 'line
of best fit', which may or may not be a perfect fit, but perfection is
never guaranteed. You normally wouldn't notice though unless extreme
settings are used.
PNG does loss-less compression just like ZIP does, but they cannot
compete with JPEG on compressed file size, they may still be too big
to email (as maximum attachment/email sizes depend on so many things).
Although there would be no point converting from JPEG to PNG.
You should be able to cram a single good quality JPEG into a 1MB email
though (much less I would have thought), and a single 1MB email should
not be a problem for most systems. Other techniques would be better
though as Jason says.
--
Lee
More information about the thelist
mailing list