Hi André,
Welcome to the CiC forums from me, great to have you join us, especialy with such a lovely picture.
Willie, Tim and Paul have that angle well covered, so I'll jump on my hobby horse
and answer your question
Personally, I would strongly recommend that for internet use, you change the units from cm to
pixels when resizing for online use.
If you use cm, how big it appears depends upon the ppi you have set, we don't know what that is and you could catch yourself out one day by changing the ppi (to do a print) and all your internet images start coming out a different size (unless you remember to compensate by choosing a different cm size).
I don't know how you arrived at that 30cm figure, but of course, although 30cm (12") is about the horizontal size you'd want it across a typical 23" (diag) monitor, there is no correlation between the two sizes - the internet works on pixels only and what physical size they appear to viewers depends on their screen size and resolution, plus many other things.
When I said "the internet works on pixels" I meant some things happen at specific
pixel dimensions, like 'maximum size' limits, etc. and it will be impossible to predict (without in-head maths) when these things are going to affect your pictures (usually adversely
)
For example, the images in the CiC forum re-size to 700 px for display inline - if you click them, you see them bigger, sometimes life size, other times less (depending on many factors). Why does that matter?
Your images actually come out at 850px across, so CiC resizes them to make them fit the page nicely and in the process, they will appear a little softer because any output sharpening you applied after the downsize to 30cm gets 'diluted' in the downsize.
Try a test;
First ensure your browser isn't also zoomed (that's another thing that
really makes images look soft when they aren't), so press Ctrl + 0 (zero),
Then hit F11 on keyboard to get rid of the browser header and footer panels,
Now have a look at your picture, specifically at the edges and fine detail,
Now click the image; it should open in a Lytebox a bit bigger, it is sharper, isn't it?
Our associated TinyPic hosting service has a 1600 pixel (on longest side) limit
The CiC albums maintain a 700px (on longest side) limit
If those sizes are exceeded, both will
permanently downsize your images to their mximum when saving to them (although you have not needed to use them).
So yes, you do need to downsize, rather than leave at original resolution, but please do it to a pixel size
Sorry to labour the points here, but;
a) I did warn it was my hobby horse and
b) even if you knew some or all of this (oops, sorry), many others may not and they are here to learn too
Dave dis-mounts from hobby horse
Cheers,