~4,000 pixels wide (4096 × 2160 DCI or 3840 × 2160 UHD) — four times Full HD. Cinema and premium streaming standard; demands heavy storage and processing.
Four thousand pixels wide – that's the benchmark for what we call true 4K. On set, this specifically means you're shooting with approximately 4096 × 2160 (DCI 4K, the cinema standard) or 3840 × 2160 (UHD, for streaming and broadcast). This is four times the pixel count of Full HD, and yes, you can see the increase in sharpness – but only if the optics, sensor, and lighting cooperate. A cheap 4K camera with poor lenses is quickly worth less than a 2K recording with high-quality glass.
The practical side: Shooting in 4K means three things simultaneously – storage, processing power, and workflow planning. One hour of 4K footage (depending on codec and bitrate) consumes 600 to 2500 gigabytes. You'll need multiple external hard drives on set, fast backup routines, and a DIT to keep an eye on everything. In the edit: proxies are not a luxury, but a matter of survival. Anyone editing 4K footage at full resolution in the timeline will spend more time waiting for the computer than for inspiration. Many editors work with 1080p proxies generated from the camera original – the edit runs smoothly, and the full resolution is reloaded during conform.
Technical detail: The difference between DCI 4K (4096 × 2160) and UHD (3840 × 2160) is small but relevant. DCI is the true cinema format – 17:9 aspect ratio, and every major studio demands it. UHD is wider (16:9) and has established itself in the consumer market and for streaming. Netflix shoots almost everything in 4K today because compression works better and bitrate requirements decrease when you start with native resolution – this isn't purism, it's economics.
Realistic expectation: 4K is only worthwhile if you plan to edit and grade later – and if the monitor and the viewer's eye can resolve it. A 4K smartphone video on a 55-inch TV from 3 meters away is optically a different beast than on a cinema screen. For documentaries and smaller productions, 2K is often sufficient, costs less, and requires less infrastructure. However, for those shooting for cinema or premium streaming, 4K is unavoidable – it's now the expected standard.