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Have you ever wondered why 4K videos look so much better than 1080p videos, even on your 1080p monitor?  The answer is more than “too much compression.”  The loss in detail is due to a practice called chroma subsampling and how it has been limiting a limiting factor on virtually all 1080p video that has ever been captured on a smartphone or even on professional DSLRs.  However, what makes phones that can capture 4K video like the Galaxy Note 3 so revolutionary is that we are finally able to overcome the limitations and produce real 1080p HD video, at a higher detail than even a lot of professional video recorders.

What is Chroma Subsampling?

When you compare the 100% crops of 1080p video straight out of the Galaxy Note 3 or any smartphone or even a dedicated video camera compared to 4K video resampled at 50% of it’s original sized (interpolated 1080p video), you should be able to see a big difference in quality.  It is due to a limitation brought on by chroma subsampling in the 1080p video on the left.
To understand what chroma subsampling is, let’s imagine a grid of pixels representing 1080p video.  It is approximately 2 million individual dots of color.  Let’s zoom into a single pixel, which is made up of 3 different pieces of data.  The luma value Y that tells us how bright that pixel should be.  And the two chroma values Cb andn Cr that tells us what color the pixel is.

4:4:4 vs 4:2:0

In a perfect world, every pixel should have it’s own Y, Cb, and Cr value.  This is known in the industry as 4:4:4.  However since we’re dealing with 2 million pixels, that is quite a bit of data.  And what engineers have figured out is that as long as we keep the luma (aka brightness) information of each pixel, we can share the color data of one pixel data with 3 neighboring pixels.  What this means is that 75% of the color information is discarded but the benefit is we are left with 50% less data.  This is known as 4:2:0 chroma subsampling.  It is how every smartphone, pocket camera, slr camera, and even most video cameras record video today and probably will continue to do until the foreseeable future.

No Consumer Demand To Improve 1080p Video Recording

Even with chroma subsampling, 4:2:0 1080p video still looked good enough to be called HD just a few years ago.  However, as our technology and tastes improve over time, we see that 1080p video, still has a fairly large room for improvement.  Unfortunately, all consumer video recording devices have conformed around the idea of 4:2:0 chroma subsampling and never looked back.  And although we have reached a point in our consumer electronics to handle the data of 4:4:4, there really isn’t any push to improve 1080p video recording. Some cameras that are being launched today are coming with the ability to capture 4:2:2 video with an external recorder. 4:2:2 is slightly better than 4:2:0, but it is till not as good as uncompromised 4:4:4.

4K Picking Up Where 1080p Left Off

So this is where 4K comes in to improve existing 1080p video.  In a single pixel of 1080p video, there are now 4 pixels at that same location when shooting with 4K video.  And even though 4K itself is also being recorded with 4:2:0 chroma subsampling, when we extrapolate 1080p video from it, all pixels in the extrapolated 1080p video have their individual Y, Cb, and Cr values.  Thus we are reconstructing 4:4: 4 1080p video.  And this shouldn’t really be taken lightly.  4:4:4 1080p video has been the proverbial unobtainable unicorn for even professional cameras costing of upwards of 10’s of thousands of dollars until just recently.

Always Shoot in 4K Whenever Possible

In conclusion, even if you never buy a 4K TV for the rest of your life, you can still benefit from recording in 4K, pretty significantly on a 1080p monitor.  Always shoot 4K video whenever possible.

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