4K is a bigger number than 1080p, but that doesn't mean it's better. This is especially true when it comes to 1080p Blu-ray video compared to 4K streaming. There's more to a video's quality than resolution, and Blu-rays have it.
The Elements of Picture Quality
Terms like "4K UHD" or "1080p" refer to only one factor that makes up overall image quality. Specifically, it refers to the number of pixels or "picture elements" in each frame of video. A 4K UHD (Ultra High Definition) image has around eight million pixels, while a 1080p image has a "mere" two million or so individual pixels.
While this means that a 4K image technically has four times the fine detail of a 1080p image, this is not the only thing that matters to our perception of image quality. That's why the assumption that any 4K video will look better than any 1080p video is flawed.
Several other factors have a major impact on image quality:
In general, Blu-rays have an advantage over 4K streaming videos regarding bitrate and color depth, which we'll unpack below. They're also much less compressed, so you won't see compression artifacts. Especially since the disc is mastered and quality assured before being mass-produced.
Blu-ray's Bitrate and Color Depth Advantage
A 1080p Blu-ray disc typically has a much higher bitrate than a 4K compressed video stream. This means the Blu-ray can use more data to represent each frame, resulting in a clearer and more detailed image than the highly compressed 4K video stream. The extra data allows for a wider range of colors, more detail in the shadows and highlights, and less visible compression artifacts such as pixelation and blurring. You'll often hear of "crushed" blacks in compressed video, which refers to the loss of details in dark areas.
A typical 4K stream might consume around 25Mbps
while a standard Blu-ray uses around 40Mbps, but don't forget that the
4K stream has four times the pixels, so the bitrate advantage on a
per-pixel basis is significantly more than these two numbers suggest by
themselves.
The ability to see the difference between 4K and 1080p video depends on a few factors, including the size of your screen, how far away you are from the screen, and the quality of the video itself.
Video quality can also impact your ability to see the difference between 4K and 1080p. If a 4K video has been compressed heavily or is low quality, it may not look better than a high-quality 1080p video regardless of where you're sitting.
Another wrinkle to this story is that modern 4K TVs have become very good at upscaling 1080p video to 4K. In the case of 1080p Blu-ray content, the high bitrate gives the upscaler a lot to work with, so in the end, the upscaled Blu-ray may be very 4K-like in resolve while maintaining the color depth and motion detail advantages of Blu-ray.
Blu-ray Audio is in Another League
Thanks to higher bitrates and less compression, Blu-ray audio generally offers better sound quality than typical streaming audio.
In contrast, typical streaming audio often uses lossy compression, meaning some audio data is discarded to reduce file size. While this compression can help streaming audio to be delivered more quickly and smoothly, it can also result in a loss of detail and a more compressed, less dynamic sound.
That said, it can depend on your specific audio equipment. You may not notice much difference if you don't have sound equipment to take advantage of that extra clarity. If your audio goes through a Bluetooth system, even Blu-ray audio becomes compressed with a lossy audio algorithm.
Streaming Artifacts Can Spoil Your Fun
Common visual artifacts that can occur with 4K streams on services like Netflix or Hulu include compression artifacts, banding, and macro blocking.
Banding occurs when the image has visible gradients of color rather than a smooth transition. This can be especially noticeable in areas with subtle color gradations, such as skies or shadows. Banding is caused by the limited bit depth of the video, which can result in color information being lost during compression. Even on a 1Gbps connection, your author witnessed severe banding in Amazon's The Rings Of Power streaming at 4K, along with prominent color and motion issues.
All of these visual artifacts can affect the viewing experience by reducing the detail and clarity of the image. They can be especially noticeable on larger screens or with higher-end equipment, but the difference is obvious on even entry-level modern displays.
Grab Those Blu-rays While You Can
There's a good chance that Blu-ray will be the last mainstream optical format. Going ahead, your only option may be to buy or rent digital movies and series. Of course, just like you can buy lossless digital music today, you'll likely get to buy massive digital video files that equal Blu-rays in quality. Then again, it will be some time before routinely downloading 50GB of data for a single movie becomes commonplace.