The better the file you send us, the better the print. But here's a few tips from the guys that run some of the best printers and software for inkjet in the world so no matter what you read on some webpage, here's the truth from guys that really know.....
Please don't "rez up" or increase the native file size of your photo file to make a big print. Our RIP software does a great job of that for you AND it knows what's in your file, what ink we are using, what the printers are set to for resolution and speed, and will specially rez up your file on the fly to the exact paper and printer combo we choose. It can do a better job that you can {with a few exceptions of course}.
We will accept a .jpg, a .tif, a .pdf with a color profile embedded and if you really are in trouble we will accept a .png or .psd file from a current version of Photoshop. 8 bit or 16 bit is fine, just don't over process the file in your software tools? The best photogra[hers let the camera do the work and collect the info.
No RAW files please folks, you make the conversions as you like with a TIF being first choice in the AdobeRGB color space if you have an Adobe RGB capable monitor. If you are working on a laptop or an sRGB monitor, export to sRGB. Listen, there's nothing wrong with sRGB - it's fine. We're far from a snobby snooty joint here. In our portrait studio, we shoot jpegs all day - no RAW at all and we make 24x24 b&w prints that make Dads smile and Moms cry.... all shot sRGB jpegs in b&w mode right in the camera. Trust the technology!
If we get a file in and we see trouble, we'll call you ok. If it's over sharpened or the resolution is too small or you read somewhere to use the ProPhotoRGB gamut and your color is a wreck, we'll call before we make a print. We cannot fix it, but we'll save you the trouble of paying for something you are not going to like.