[misket]

I am very new to image manipulation programs. I can do most of the basic stuff, even use layers to some extent. (I have more experience with paint.net) I've searched the forum, but then realised that i didn't know what to search for, so here goes my question.

I have scanned a fabric that my company produces. (attached is a cropped small part of it.) My goal is to understand how much percentage of empty space does the fabric have. The red color in the back is a colored paper to emphasize the difference between the fabric and the background.

I use the 'select by color tool' for the entire fabric, but when i try to select the shadowy places some dark parts of the fabric also show. Is there another way to select these empty spaces; maybe another color selection tool or some script. I also thought that maybe the software can determine that there is an ampty space by checking the vector for the fibers.

I've sent it to a commercial fabric analysis software seller, and they were able to analyze more accurate than my crude method with gimp. But i want to use open source and frankly don't want to pay for such a minute task.

Thanks in advance.