you could use photo studio easy tools for basic renderings in catia. the icon for it is located on the bottom row of tool icons, and it looks like a camera. im not sure how much you know about it already, but its not difficult to use.
Use the photo studio tool at the bottom ..i.e. a camera select the part , use the pixel setting also you can adjust the contrast, brightness etc.. Also the type of light source can be adjusted. If you got any problem contact me.