Chroma Key pictures In Vegas 7
 

I need some help with sony vegas 7 please! I've taken some beautiful HD green screen pictures. I know how to chroma key and make it perfect, but how do I save the file as a picture? If I save it as and PNG or JPG, when I open them to print, they are small and grainy when you print them. Can anyone tell me how to save these pictures as larger files to print in vegas?

Welcome to the forum Amy.
I'm sure you'll find us a bunch of friendly and helpful folks.

Make sure your Preview window is set to Best/Full before taking a snapshot of it.

snapshot?
 

What do you mean when you say take a snapshot of it?
I set the preview to Best-Full, looks much better, but when I print, still not getting the desired results.

By snapshot I mean taking a still frame of wherever the cursor is on the timeline.
Folks do this to either grab a still frame for later use or for printing purposes which is what I thought you meant.

If this isn't what you meant, please clarify exactly what you want to do.

Amy,
When you "take a snapshot" or a freeze frame of the image in Vegas it is taken and saved at a very low resolution. Hence it is small and when enlarged to any degree it becomes grainy and downright ugly. ;-)
Generally when I need to print something off the timeline I take my "snapshot" or freeze frame then bring the PNG into Photoshop and massage it there. Usually the 1st thing I do is bring the resolution up to double the original (gotta be careful with that though-if the frame grab you're working with isn't free of interlacing or has the jaggys or any motion blur at all it will make for an ugly look) then I'll resize the shot if possible to fit to a size of no more than 5X7 and many times 4X6. It's been my experience that anything over 5X7 will come apart at the seams so to speak and look terrible even at the higher resolution. Remember VEgas is a great NLE but not really made for pulling high res stills so you have to work with what it'll give you which is a low res image that works fine for small image printing.
I do this routinely for my custom DVD cases, pull snaps at 72 dpi, into Photoshop bring to 150 dpi and when printed the shot is NEVER even 5X7 and if it is used as a background shot I blur it a bit in Photoshop but that a rarity.
If you have any kind of photo editor then bring the PNG or JPG into it and play around a bit. I think you'll find better results but remember, keep the prints small.

When you save as a photo format, it is going to save at the current project resolution, or lower if you have the preview set to half or quarter and take a snapshot. If you took a photo (not a video grab) then I'm guessing it has a much higher resolution than whatever your video project is set at. Maybe find a way to up the project resolution 2k? 4k? and then do your keying/saving. I guess I'm not sure when you say photo, you mean a still photo taken as such, or just a frame you picked out that was recorded as video. Hope this helps!

NOTE: Vegas Pro 9 and 10 now save snapshots at the best, full size, resolution automatically. While this does simplify things somewhat for the end-users, it also removes some of the flexibility.

Thanks everyone for your help. It would appear that I need to use Photoshop or some other photo editing software to get the desired results. Thanks again!