This might sound familiar. You’re recording video on your digital stills camera, pleased that it has a movie capability as well as its stills photo facility.

Then, when you get home, you pause the video mid-edit and realise that a particular frame would make a great picture. If only you could save that single frame as a still image, you’d have a usable picture. 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 produce a printed picture. This is partly because a video screen is somewhat forgiving. Television screens are big and self-illuminated, each pixel can be any colour you want and you tend to view them from across the room.

Print images have much more detail. You view them from closer distances, and creating a coloured dot involves a complex process of combining lots of smaller dots of just a few colours. Consequently, when you shoot video, you’re not capturing as many pixels per frame as when you shoot with a stills camera.

For example, shooting a still frame on a Canon S90 point-and-shoot produced an image that’s 3,648 x 2,736 pixels. At 240 pixels per inch (ppi), which is what most photo inkjet printers need, we can print that image at 15.2 x 11.4in. But when shooting standard definition (SD) video with the same camera and extracting a single frame, we got an image that’s 640 x 480 pixels. At 240ppi, that file produces an image of only 2.6 x 2in.

If your camera shoots SD video, you’ll find that the low pixel count makes extracting stills a dubious proposition. Fortunately, these days many cameras shoot HD videos, which have higher resolutions. The Panasonic GF1 shoots 720p HD video, from which you can pull a still image that’s 1,280 x 720 pixels – good enough to get a reasonable (180ppi) 4 x 7in print. The image has a 16:9 aspect ratio, which means it will need to be cropped if it’s destined for a standard 4:3 or 3:2 frame.

You can use Apple’s Aperture 3 to scrub through video footage and create a JPEG of a single frame

How to extract the frame
There are a number of ways you can 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 x 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 Cmd-1. Press Cmd-Shift-4, and your cursor will turn into cross hairs. Click and drag to pull a selection around your video window. When you release the mouse button, an image file will be written to your desktop. If your video won’t fit on your screen, you’ll need to use some extra software, such as Snapz Pro X (www.ambrosiasw.com) to write out a still frame.

Export from iMovie You can use iMovie ’09 (www.apple.com/uk) to export a still. First import the clip into iMovie, then create a new project. In the Project pane, scrub through the video by moving your mouse over the clip. When you find the frame you want, Control-click (or right-click) and choose Add Freeze Frame from the drop-down menu. A new clip will be added to the end of the segment. Control-click (or right-click) on this frame, and choose Reveal In Finder from the menu. A Finder window will open that shows the newly created JPEG. Unfortunately, this function has been removed in iMovie ’11.

Use Aperture To use Aperture 3 (£45 from the App Store, www.apple.com/uk) to create a still, import a movie into it, play it until you find the frame you want, and then open the menu on the right of the playback controls. Choose New JPEG From Frame, and a new still frame will be added to your project. Click this and choose File > Export Version to save it as an image file.

On the iPhone If you take videos on your iPhone, MovieToImage (www.iphoneography.com) is a 59p app that grabs stills from these. Use the scrubbing interface to locate the frame you want. When you find the perfect shot, tap the Save button in the bottom-right corner. The still will be saved to your Camera Roll.

Give it your best shot
When choosing a still image, have a subject and a background, a shot that fills the frame, and nice light. Although this can’t match what a good stills camera can produce, you should be able to get a nice still frame if your camera shoots quality video.