Format of pictures for textures, materials etc.

Hi there,

I have been trying to find out a way to calculate the minimum image sizes that you can use for rendering when it comes to textures and materials. I am thinking that it would be great to use the smallest size possible without loosing any information/pixels from the images.

1. What are your takes on this? Do you usually go for as big as possible to increase quality, or do you scale down images for its purposes depending on how big the rendering will be, and in that case, how do you calculate it?

2. Another related question is what format of the pictures you use, jpg, png, tiff etc, what are the pros and cons for these? When I save images for my homepage for an example I always save them for web, meaning compressing them into MUCH smaller jpg. Is this a workflow that is suitable for rendering as well, when you are not supposed to print the renderings?

A lot of questions, and I am very new to this area, love it and will try to get as good as I can creating professional renderings.

Appreciate all help,

Fredrik