You seem to see 4k everywhere today. There are 4k tv's, 4k computer monitors, and even most new cameras can shoot 4k video now, including smartphones. So what exactly is 4k video and what if I told you all "4k" is not the same?
When someone is talking about 4k they are referring to resolution size. Full HD video is 1920 by 1080 pixels. The most commonly thought of 4k video or UHD (Ultra High Definition) is 3840 by 2160, four times the amount of pixels in Full HD. Another form of 4k video is DCI 4k. Its resolution size is 4096 by 2160 and is mostly used in the film industry for the wider aspect ratio. The picture bellow can help visualize the different sizes.
Resolution size also isn't the only differences in 4k video. The quality of the video can vary dramatically. 4k shot on your iPhone will look worse than 4k shoot on a Red Epic because of sensor size and bit rate. An iPhone has a smaller sensor size and records at a smaller bit rate than a Red Epic so it's 4k video, while being the same resolution size, will not look as good as 4k shoot on the Red.
So why would you want to film in 4k? That question we answer next week!