" the quality of the picture is no the best"
In what way?
Do you look at the image at the scale 1:1? (sorry if it is too obvious for you, some people just overlook simple things)

AFAIK, the PPI setting isn't relevant for most image formats: it is just an indication for rendering purpose, but what is relevant is indeed the number of pixels the image stores.
Jpeg can alter the image to reduce the size of the file (that's a "Quality" setting, I think Processing sets it high by default).
Tiff can store images in Jpeg format internally, or in other formats. It is a wrapper format with various stuff inside.
Have you tried the PNG format? It can make bigger files than Jpeg, but it is pixel-perfect.

As PhiLho says, for printing the only things to take care are number of pixels and color space. If you want a hires output use a tiff format, it has no compression algorithm at all. As I use metric system the quick rule I apply when want a hi-res print is a factor of 0.0084 ( 2.54 cm. (1 inch) / 300 ppi ). That's it, an image of 1600 x 900 pixels corresponds to a 13.44 cm x 7.56 cm. print at 300 ppi. If you print the output at that size using gimp, photoshop or whatever you'll had the print at that quality.
The proper way to do it, though, is just the opposite: if you want to export an A3, for instance, you´ll need a 42 / 0.0084 x 29.7 / 0.0084 image, that's it, a picture of 5000x3536 pixels.

Hope it helps and regards.

Ale · http://60rpm.tv/i

thanks guys for your response. I will try it and see what happend.