Image re-sizing
 

Sorry for what might be an obvious question to most but I would
appreciate a little advice on re-sizing an image.
I currently have an image which is appreox 3.4 mb which I have been
asked to send via e-mail at 100k.
Using photoshop I go to Image size and adjust the pixel dimension to
340 x 252 and save the JPEG at highest quality (12) and 72 pixels/inch.
However although the image is very good when I send the image it
appears quite small. Saving the image at a lesser image quality for a
smaller file increases the size dispalyed but the image is noticeably
poorer when dispalyed.
I am a little confused however in that I have an e-mail which has been
sent to me which has various pictures attached.
These are reasonable quality (on monitor),display a larger image when
opened, yet are only 30-40k in size !
I would appreciate therefore any (easy) advice as to the best method to
produce a 100k image which is going to give the best quality but yet be
dispalyed at a reasonable size when sent.
( I understand quality v size is probably a trade off ) but your help
is appreciated as to date I havn't really had to bother in reducing
files for this purpose.

Rob.

On Fri, 01 Apr 2005 05:02:39 -0800, Eos wrote:

snip
I would appreciate therefore any (easy) advice as to the best method to
produce a 100k image which is going to give the best quality but yet be
dispalyed at a reasonable size when sent.
( I understand quality v size is probably a trade off ) but your help
is appreciated as to date I havn't really had to bother in reducing
files for this purpose.

Rob.

Size versus quality is an inevitable tradeoff. There is no easy way to
tell how much quality you have to sacrifice to get to a certain file size
since the complexity of the image plays a major role in the amount of
compression you can achieve while retaining acceptable visible quality. Of
course reduction in pixel size will always help while maintaining visible
quality so that's a good start. What's the minimum required pixel size for
your recipient? Once you have that, save the picture at that size and
start increasing compression (=reducing quality) until you get a file that
fits inside 100KB. My personal experience is that images don't suffer a
whole lot when using Photoshop's JPG compression setting 8 but still
compress quite well. Usually you can even go a few steps further down, but
editing the resulting JPG will be out of the question because of very
noticable compression artifacts. So do your editing on the orignal and
compress that.

Hope this helps

Bas

On Fri, 01 Apr 2005 05:02:39 -0800, Eos wrote:

snip
I would appreciate therefore any (easy) advice as to the best method to
produce a 100k image which is going to give the best quality but yet be
dispalyed at a reasonable size when sent.
( I understand quality v size is probably a trade off ) but your help
is appreciated as to date I havn't really had to bother in reducing
files for this purpose.

Rob.

Size versus quality is an inevitable tradeoff. There is no easy way to
tell how much quality you have to sacrifice to get to a certain file size
since the complexity of the image plays a major role in the amount of
compression you can achieve while retaining acceptable visible quality. Of
course reduction in pixel size will always help while maintaining visible
quality so that's a good start. What's the minimum required pixel size for
your recipient? Once you have that, save the picture at that size and
start increasing compression (=reducing quality) until you get a file that
fits inside 100KB. My personal experience is that images don't suffer a
whole lot when using Photoshop's JPG compression setting 8 but still
compress quite well. Usually you can even go a few steps further down, but
editing the resulting JPG will be out of the question because of very
noticable compression artifacts. So do your editing on the orignal and
compress that.

Hope this helps

Bas

How well an photo will compress depends on the content of the image,
lots of sky or an photo with the background out of focus will compress
more then a photo that is sharp and has lots of detail, like grass,
sand, trees.

Normally 100K would be good for about an 640 x 480 image but might be
able to go up to something like 800 x 600, this depends on how much
detail is in the photo. The best thing to do is to try saving it at
different sizes and see how they look. Do "Save For Web" this
strips off the EXIF data which will save some room and it allows find
control on the quality used to save the photo.

Scott