Today’s compact cameras can often shoot both video and still images, but not at the same time. Christian is looking to save high-quality pictures from his home movies

I would like a compact camera that can take 20MP photo stills from the video. Something about the size of a Fuji X30 would be nice. Can you point me in the correct direction? Christian

You can’t have what you want at the moment, and there are technical reasons why it’s difficult. However, cameras and smartphones that can shoot 4K video can produce passable 8.3 megapixel still images. With a bit of post-processing, they should be good enough for most practical purposes.

You may need to do some digging to find the product that best meets your needs, but there are four things to look for. These are, in descending order of importance: (1) 4K video capability; (2) a built-in “save frame” feature; (3) a 16-32MP image sensor; (4) an electronic viewfinder or EVF. You can tune your requirements at DP Review.

Video screengrabs

Facebook Twitter Pinterest In TV and cinema projection, each movie frame is shown twice, or sometimes three times, and ‘persistence of vision’ does the rest. Photograph: Lambert/Getty Images

Video is an illusion created by presenting a series of still images in rapid succession. The SMPTE (Society of Motion Picture and Television Editors) standardised on 24 frames per second (fps) in 1927, and we’re now used to it, though 30fps is also common. In TV and cinema projection, each movie frame is shown twice, or sometimes three times, and “persistence of vision” does the rest.

However, the actual quality of each image is rather low. This becomes obvious if you take a “screengrab” of a video using image capture software such as the snipping tool in Microsoft Windows, or a video player than can save frames, such as VLC.

Even a Full HD or 1080p video only has a frame resolution of 1920 x 1080 pixels, which is roughly 2MP. This is why you’re not going to get 20MP. However, some still cameras can capture 4K video, AKA 2160p, where each frame has a resolution of 3840 x 2160 pixels. Capturing one of those provides your 8.3MP still image.

The 2160p resolution is used for UHD-1 or ultra-high definition TV broadcasts. The main drawback is that it uses a lot of data: a single movie can easily consume 40GB. For comparison, a standard DVD stores 4.7GB.

Motion JPeg v video

Still cameras are obviously designed to capture still images, but as digital cameras became more powerful, some could capture a series of stills in rapid succession, ie a movie. This format is known as Motion JPeg or M-JPeg. The important point is that each image is complete and self-contained.

M-JPeg involves a trade-off between resolution and frame-rate, and early digital cameras had to use very low resolutions to capture enough frames to show movement. To quote Wikipedia, “resolutions of 160 x 120 or 320 x 240 are common sizes, typically at 10, 12 or 15 frames per second”.

Things got serious when Nikon launched the D90 digital SLR in 2008. It could capture M-JPeg movies in 640 x 424 and 1280 x 720 pixels, and the results were impressive for the time. I bought one, and I’m still using it.

The current champion is the Canon EOS-5D Mark IV, which can capture 4K video (actually, 4096 x 2160 pixels) in M-JPeg, which requires a data rate of around 500Mbps. The 5D Mark IV is not compact and, at £4,000, not cheap. Nor is the £5,000 Nikon D5, which has a Live Frame Grab feature. Either of those would give you the highest quality still images, though they still have problems, such as the “rolling shutter” or “Jello effect”.



Of course, today’s digital movies are no longer a series of stills. The idea behind compression systems such as mp4/H.264 is that you only capture a few full frame images. After that, you just provide the changes needed for the next frame. This works brilliantly if the image is static, such as a TV newsreader. It starts to break down with fast action. If you need to send almost the whole frame each time, the system can’t cope and shows blocky artefacts or even small green squares.

You can capture or export single frames from compressed 4K videos, but really, only the “key frames” provide the best quality. The images that are constructed on the fly are of variable quality, and probably worse than M-JPegs.

What about a smartphone?

Facebook Twitter Pinterest Stills from smartphone videos tend to suffer from motion blur – from shaky hands and slow effective shutter speeds. Photograph: Alamy Stock Photo

Still cameras did M-JPeg videos instead of using codecs because it takes a lot of expensive processing power to handle video compression, and they didn’t have it. Smartphones, by contrast, are built around powerful processors, and some can now shoot 4K videos. If you have one, it should be possible to save frames as 8.3MP stills. You can do this on Samsung Galaxy smartphones, for example.

Stills from smartphone videos tend to suffer from motion blur – from shaky hands and slow effective shutter speeds – and artefacts. Also, smartphone image sensors and lenses are not as good as the ones on decent compact cameras. But it’s worth experimenting with whatever smartphone you have. You’ll be better informed when you choose your digital camera.

Possible products

Panasonic’s digital cameras gained a good reputation for shooting high-quality videos, with most fans not even realising that the company also makes broadcast quality professional equipment. The 16MP Lumix G7 mirrorless became popular for 4K video, but the current favourite is the Lumix GH5, which can record 4K video at 60fps.

When Panasonic launched the LX100 compact camera in 2014, it introduced a feature called 4K Photo mode. This lets you step through your 4K video on the camera screen and save still images, which is usually more convenient than moving the video to a PC to extract frames.

In this case, your best option might be the 16MP Panasonic Lumix DC-GX800 (or GX850). It’s very compact, it shoots 4K video at 30fps, and it has the 4K Photo mode. It has drawbacks – narrow zoom range (12mm to 32mm), no EVF, no hot shoe, limited video controls – but it’s terrific value at £379 on Amazon.

Facebook Twitter Pinterest The Lumix GX800. Photograph: Panasonic

The Lumix GX800 is essentially an entry-level version of the Lumix DMC-GX8. This has a superior 20.3MP sensor, a 3x (14-42mm) zoom, an in-body image stabiliser, a hot shoe and a great EVF. However, it’s also larger and more than twice the price at £877.70.

If you’re willing to spend that sort of money, check out the Sony RX100 V. Yes, £899.99 is still a silly price for a compact camera with a 3x optical zoom lens, but you get advanced technology for your money.

The Sony RX100 V is remarkably small and light for a 20.1MP camera with a one-inch sensor. It has a “stacked sensor” that’s integrated with memory to collect data five times faster, according to Sony, and a high-speed electronic shutter. It can shoot still images at 24fps in both JPeg and RAW modes. Its 4K video is oversampled from 5.5K video (5,028 x 2,828 pixels), with the maximum resolution being 5472 x 3648. From the specs, it should produce better quality stills than the Lumix GX800, and it’s much smaller than the GX8 and your Fuji X30.

You can compare the various cameras side by side at DP Review, while Camera Price Buster is brilliant for price comparisons. Good luck!

Have you got a question? Email it to Ask.Jack@theguardian.com

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