my camera is a 15 mp camera, therefore it takes pictures up to 4752x3168 pixels. When I open a picture in photoshop and look into the image size it will say 72 dpi and 66 inches width by 44 inches height. I am used to changing the resolution to 300 and so it will automatically change the width and height to 15.84x10.56 inches but the pixels of course will remain the same(4752x3168). I also change it to CMYK. So my question is what if I want to print a large format (30 x20 inches) should I live the image size as it is when opened, in 72 dpi? or should always change the resolution to 300? or should I change it to 30x20 and link the resolution so that the pixels will remain the same but the resolution will automatically change accordingly. In this case 158.4. Is it ok to print photographs in CMYK? what kind of printing companies print large format pictures?