There are many companies out there to deceive customers and hold back the industry but none more so than the likes of Nvidia.
It seems many other sites are reaching up for the stars at the sight of two latest monitors released by ASUS and Acer. The ASUS ROG Swift PG27UQ and Acer Predator X27. Both monitors are 4K (3840×2160) “144Hz” HDR displays featuring Nvidia’s latest G-Sync HDR module. Both monitors are currently retailing for $2000 USD and hidden beneath that price tag lies a whole lot of bullshit.
4K resolution 144Hz and with added G-Sync and HDR no less this almost sounds too good to be true and well…. it is. These monitors are advertised as 144Hz but really that’s an “up to” 144Hz from the base of 120Hz but that’s not all only up until 98Hz can you utilize the added benefit of 10 bpc colour depth otherwise known as HDR. And even with a standard 8 bpc colour depth can you only go up until 120Hz as anything more than that results in a lower quality image and here’s why.
Sounds scary I know but there is nothing to fear as Chroma subsampling is a method of reducing bandwidth by partially lowering the resolution of an image.
Imagine you have a full colour 4K image with three values of RED, GREEN and BLUE with values of 0-255, three separate monochrome images, a 3840 x 2160 grid of RED, GREEN and BLUE values to overlay on each other to construct the final image.
Now imagine that you have reduced the resolution of the RED and GREEN to 1920 x 1080 and you reconstruct the image upscaling to a 4K screen use each 1080p pixel value for a square of 4 pixels on the 4K screen. This upscaling is only done for the RED and GREEN values as the BLUE image is still at full resolution so BLUE has a unique value for every 4K pixel.
The general thought behind chroma subsampling is reducing the resolution on a portion of the pixels but not all.
Full resolution on all components is known as “4:4:4” or just plain ans simply non-subsampled.
4:2:2 subsampling is cutting the resolution in half in only one direction (i.e. 1920 × 2160; horizontal reduction, but full vertical resolution) on 2 out of the 3 components. This reduces the bandwidth by one third.
Chroma subsampling is not a form of compression, because it doesn’t involve any de-compression on the receiving side to recover any of the data. It is simply gone. 4:2:2 removes half the color information from the image, and 4:2:0 removes 3/4 of it, and you don’t get any of it back. The information is simply removed
The method mentioned above for subsampling was only an example and a pretty terrible one at that as RGB subsampling is not commonly used on its own at all instead commonly used in combination with YCbCr. YCbCr is a different method of specifying colors, used as an alternative to RGB for transmission. YCbCr is useful because it specifies brightness and color separately.
Subsampling components also works much better in YCbCr, because the human eye is much less sensitive to changes in color than it is to changes in brightness. Therefore you can subsample the chroma components without touching the luma component, and reduce the color resolution without affecting the brightness of each pixel, which doesn’t look much different to our eyes. Therefore, YCbCr chroma subsampling (perceptually) affects the image much less than subsampling RGB components directly would be. When converted back to RGB of course, every pixel will still have a unique RGB value, but it won’t be quite the same as it would be if the YCbCr chroma subsampling had not been applied.
Quite a few years back we saw examples of this back when Nvidia added 4K 60Hz support to graphics cards with HDMI 1.4 while HDMI 1.4 was only capable of 30Hz at 4K but with 4:2:0 subsampling which reduced the bandwidth by half the refresh rate was able to increase within the same bandwidth limitations all at the cost of image quality.
Chroma subsampling reduces image quality. Since chroma subsampling is, in effect, a partial reduction in resolution, its effects are in line with what you might expect from that. Most notably, fine text can be affected significantly, so chroma subsampling is generally considered unacceptable for desktop use. Hence, it is practically never used for computers; many monitors don’t even support chroma subsampling.
As mentioned above these monitors are pushing 4K at 144Hz but DisplayPort 1.4 only provides enough bandwidth for up to 120Hz with an 8 bpc color depth, or only 98Hz with a 10 bpc colour depth (HDR) but these monitors claim to support “up to” 144Hz so some form of bandwidth reduction has to be made and in the case of these monitors are reducing down to 4:2:2.
We have included a highly detailed image depicting just what exactly is happening once your refresh rate is higher than 98Hz.
Nvidia’s new G-Sync HDR module features an Intel made Altera FPGA (Field-programmable gate array), a very versatile and programmable processor that can be coded to suit just about any task. The FPGA inside Nvidia’s G-Sync HDR module is an Arria 10 GX 480, a mid-range product within the lineup and is also built on TSMC’s 20 nm process. With this FPGA you could get away with slapping an Intel logo on it and nobody would bat an eye.
The Altera module is seen to be using 3GB of DDR4 memory rated at 2400Mhz which is a huge step up from Nvidia’s original G-Sync module which only utilized 768MB of DDR3.
It is however speculated that the added price to the monitors themselves are upwards of $500 however it is possible to purchase this FPGA in low quantities for $2000 over at Mouser and Digikey. It’s not hard to imagine that Nvidia are purchasing these in bulk which would drive the prices down but alongside the added cost of that 3GB of DDR4 memory for these modules explains why these monitors are so expensive.
I suppose it pays to have the “best”.