Why check "output YUV data as basis YCbCr not CCIR601" ?

Because if your source is already CCIR601 ( which it probably is ), then it's better to output as YCbCr. Read the definitions here:
http://www.crs4.it/~luigi/MPEG/ccir601.html

kwag

But when you use it, the film gets out so dark that it loses some details.
Even if you increase the brightness at the monitor / TV... the details are gone.
Is it suppose to work like this?

Here's a cut+paste from the DVD2AVI page:

YUV -> RGB

Generally speaking, the color scale of TV and PC monitor is differnet.
The RGB value of pure black on PC is (0, 0, 0) On the other hand, it's (16, 16, 16) on TV.
If you want to watch the video on PC, it's better to choose PC Scale for full-scale colors.

It's hard to decide which option is correct when you watch on TV.
Video editors, encoders, and codecs all affect the color scale of the final result.
Try both scale and compare them on TV to see which one is smiliar to original source.

The link is here: http://arbor.ee.ntu.edu.tw/~jackei/d...doc/video.html

kwag

If you get too dark image then you may want to try this: In tmpgenc->settings->advanced->simple color correction->gamma=100, i hope this is not too bright for you. Of course retouching a lot is not good but you can try it and see if you like what you see.

DaDe.