size of windows image become so large after capturing

Hi

I wanted to upload some images in my WDS .after Sysprep /oobe/generalize I used wds to capture windows 8.1 x64 .

after that capturing finished I realized that the image size is 13GB and after installation that image on a pc I found that it used 30 GB of C drive .

I used disk clean up and again did the process of capturing .this time the image is 12 GB and after installation it used 25 GB of Drive C .

I believe that there is something wrong for that huge image .I expected at most 18 or 19 GB .

Would you please give me your advice ?

thans a million