The best way to do tis is with a filter present in almos every programme. The key about NTSC is to avoid oversaturated colours that might explode. (NTSC = never twice the same colour). Is you are working with still images the right choice would be photoshop. In the filters menu go to video > change to NTSC (or something like that). If you want to adjust moving images (either quicktime or image sequences) I suggest to get a copy of Adobe Ater Effects and asgain in filters it has a conversion tool. I have tried both metods to transfer to SMOKE/INFERNO and later to DigitalBetacam and they worked fine.