@Car_Dude @thenewepic
It might help to explain what information the image is helpful in determining - sorry it's a bit complicated...😉
Here are RTings instructions:
Quote from their
Learn webpage:
HOW TO TEST FOR CHROMA SUBSAMPLING
Testing for chroma subsampling is very easy. Just (download, and)
open up our test pattern in Windows Paint using a PC Preview, then observe it and check if any of the lines and text are blurred together.
If none of the text blends together and shows artifacting, then the TV and mode you are using does not use chroma compression and is showing chroma 4:4:4.
It's also important to make sure that Windows scaling is set to 100%. With larger, high-resolution monitors it is common for Windows MacOS to scale UI elements at 200% or more, and this can cause false positives when testing for Chroma Subsampling.
So, it's a test to determine if a full RGB 10 bit signal is being displayed by the monitor.
At 100% size on a Mac 218ppi monitor the image is just over 5.5 inches across - if it's not that small then the monitor's settings aren't right.
If the signal chain to the monitor doesn't have enough bandwidth for this full signal, then one way of reducing the bandwidth is to reduce the amount of colour information being sent to each 'pixel' - the group of 3 RGB phosphors that are built into the screen matrix.
This is called Chroma subsampling, and depends on an encoding algorithm called YCbCr, (sometimes shortened YUV).
Y is the
luma (brightness) component, and Cb and Cr are the
blue-difference and
red-difference chroma components.
From this, the full RGB information can be mathematically derived.
If the signal for each phosphor is fully encoded, then there is no subsampling, and this is written 4.4.4.
If the full Y information is sent - individually to each pixel, but the Cb and Cr information is sent at half bandwidth, then this is 4.2.2.
With this
each horizontal pair of adjacent R, G and B phosphors get the same balance of colour information, so there is half the colour resolution.
This subsampling is routinely done with TVs, where fine detail in colours (of moving images) are far less obvious - the eye is more sensitive to brightness than colour.
TVs mostly use HDMI for the input, and MacOS sometimes sees a monitor connected to the Mac's HDMI port as a TV (or projector), and sends a YCbCr signal - not the full RGB 4.4.4, which gives the best image on the computer monitor showing text and graphics.
The RTings test image is designed to show if the signal being sent to the monitor is using 4.2.2 compression.
If it is, then blue and red phosphors (and green!) will only be working at half resolution.
But to see this the RTings image must be displayed at 100% size (not bigger or less).
And the monitor must be set to show a full resolution image.
Which for 6K is 6144x3456.
Not half that in HiDPI...
Then a photo with a camera (iPhone) must be taken to record what the actual screen phosphors are showing.
A screen grab just shows what the Mac is sending, and doesn't show if subsampling and compression is happening on the way to the monitor... 😉
This is an example of the difference the test shows with a YUV 4.2.2 signal.
It clearly shows the halving of the resolution for low brightness strong colours.
(Taken from
@yaosiang in the
DIY 5K monitor thread,
this posting):