Fortunately, there are several ways to do just that.
What size image can you get?
It takes far fewer pixels to create a video image than it does to create a printed image. This is partly because a video screen is somewhat forgiving. TV screens are big and self-illuminated, each pixel can be any color you want, and you tend to view them from far away.
For example, when I shoot a still frame on my Canon S90, I get an image that’s 3648-by-2736 pixels. At 240 pixels per inch (ppi), which is what most photo inkjet printers need, I can print that image at 15.2-by-11.4 inches. However, when I shoot standard definition video with the same camera and extract a single frame, I get an image that’s 640-by-480 pixels. At 240 ppi, that file only produces an image of 2.6-by-2 inches.
If your camera shoots standard definition video, you’ll find that the low pixel count makes extracting stills a somewhat dubious proposition. Fortunately, many cameras these days shoot HD videos, which have higher resolutions.
The Panasonic GF1 shoots 720p HD video, from which you can pull a still image that’s 1280-by-720 pixels—good enough to get an okay (180 ppi) 4-by-7-inch print. The Canon 5D Mark II’s 1080p HD video produces an image that’s 1920-by-1080 pixels, which creates a 8-by-4.5 inch print at 240 ppi. (Note that both of these examples are a 16:9 aspect ratio, which means the image will need to be cropped if it’s destined for a standard 4:3 or 3:2 frame.)
Before you extract a still from any video, consider how big of a print you want, and then assess whether your camera can deliver a usable image. If you don’t mind a little softness, or lack of detail, then extract away.
There are several ways to go about capturing a single frame from a video.
Get a Screen Grab If you’re working with SD video (which has a resolution of 640-by-480) you can do a screen grab. Open the movie in QuickTime Player, and make sure you’re viewing at actual size. To do this, choose View -> Actual Size, or press Command-1.
Press Command-Shift-4, and your cursor will turn into a crosshairs. Click and drag to pull a selection marquis around your video window. When you release the mouse button, an image file will be written to your desktop. If you have a big enough monitor, you can even do this with HD footage.
If your video won’t fit on your screen, then you’ll need to use some extra software, such as Snapz Pro X or Screenflow, to write out a still frame.
Use Aperture If you have Aperture 3, you can create a still by importing a movie into an Aperture project, playing it or scrubbing through until you find the frame you like, then opening the little gear menu on the right side of the playback controls. Choose New JPEG From Frame, and a new still frame will be added to your project. Click on this frame and choose File -> Export Version to save it as an image file.
On the iPhone If you take videos on your iPhone, MovieToImage is a $1 app that makes grabbing stills from these files snap. No trip to the Mac is needed. Use the app’s simple scrubbing interface to locate the precise frame you want. When you find the perfect shot, tap the Save button in the bottom right corner of the screen. The still will be saved to your Camera Roll.
Give it your best shot
When choosing a still image, you want to follow the same compositional ideas that you use when taking still photographs. Be sure you have a subject and a background, a shot that fills the frame, and nice light. While no substitute for a good still camera, you should still be able to get a nice still frame if your gizmo of choice shoots quality video.
[Macworld senior contributor Ben Long is the author of Complete Digital Photography, fifth edition (Charles River Media, 2009).]