Hi
Is it a Good Idea to change 1) saturation ( is it same as Vivid in color mode ) what is
Vivid and what does it do. 2) Contrast – should contrast be increased for landscape? if yes
by how much is ideal [ should the contrast be reduced for Portrait shots? Finally should we
be messing around with Saturation & contrast mode ?
There are no pat answers to your question. It depends on a few things and your own personal taste and editing skills.
The camera - I would never increase saturation on my Canon digital cameras because they are already quite saturated by default. However, I've increased saturation in my Panasonic camera because, while very pleasing, I find Pany colors a bit dull.
Post processing - If you don't like to process photos, you may be better off increasing things like saturation, contrast and sharpness. However, if a camera oversharpens an image, it can't be undone. That's why I prefer to sharpen my own images.
You really need to experiment with these settings and find out which works best for you.
I have written about these settings in my blog:
http://www.digicamhelp.com/camera-logs/9/picture-adjust.php
