ntenny ,

I think , there is a easier way to decide your degree of noise. Otherwise you dive in to brain research on human perception of visual noise problem.
Easy way is to find the fractal degree of autochrome. Enlarge my book cover scan with a photocopier , divide it to squares and count the noise per square. When you find the ratio of noise count to square , you find the fractal degree. This is the most basic way to tell your fractal software to generate noise. May be you need to color seperate the book cover with a enlarger and count fractal count per base color.
Ultra fractal software is one of the best software to generate your noise and before you could ask help from their list. May be you can create noise on pictures with a code.

Best ,

Mustafa Umut Sarac