I exported some stills out of FCP X and made them psd. they exported at 72 ppi.
If I change the pixels per inch - does that make them higher resolution? Does that improve their quality or not?
I want to make some 'production stills' of my film and we didn't shoot any.
Short answer - No. But you can certainly make the images look better than the raw grabs. When you increase resolution PS is interpolating the existing pixels to create new ones...it does a respectable job but can't make detail where it didn't exist in the first place. I've had to do this a couple of times and here's the basics of what I learned.
-Hopefully your footage was shot Progressive. Interlaced footage tends to have jagged edges that require yet another interpolation by the Deinterlace filter in PS.
-Hopefully your subjects are not moving much and in good light.
-Make sure your footage hasn't been resized somewhere along the edit workflow!
-If you can grab your stills from the original camera footage that's usually a good thing since it avoids any changes that may have taken place in the edited timeline. I like to open the original clips inside PS and then create layers from the frames I want to grab and export them. You have to manually scroll with the mouse through the clip to find your frames, but works reasonably well.
-If you must create an image larger than the original pixel dimensions:
-I've found that increasing the resolution some (say from 72 to 200) will give me a little more to work with for the next step, which typically involve duplicating the original image, using the HDR toning under PS Adjustments tab to lower the "detail" while trying to keep the edges somewhat sharp. Every lighting situation seems to demand different settings. After developing with the HDR toning, I sometimes then stack that layer with the original image and adjust the layer opacity until it looks reasonably good. And your likely going to visit the Vibrance or Hue/Saturation adjustments along the way.
San Antonio College