can UGA-4KHDMI do 4:4:4 chroma?


#1

Can the UGA-4KHDMI do 4:4:4 chroma at 4K / 30 Hz?

Because of chroma subsampling, the cheap Changhong TV I’m using as a monitor fails this test (the red and magenta text is very fuzzy).

!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275275/444_inline.png?1442035908)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275275/444.png?1442035908)

So, I’m in the market for a better monitor, but most don’t specify whether they are 4:4:4 capable. I plan to take a laptop with the Plugable adapter around to Costco, Sam’s, BestBuy, etc. and try various monitors. However, that won’t work if the adapter itself is putting out 4:2:2 or 4:2:0 video. Can you please confirm whether or not the adapter can output 4:4:4 / 4K / 30 Hz video?

Thanks,

Stewart


#2

Hi Stewart,

Thanks for asking! Unfortunately, I’m not sure I know enough to give a confident answer. Internally, the DisplayLink chip is doing RGB 888 in its framebuffer. Then it’s outputting DisplayPort signaling, which then run one or two additional chips to finally convert to 4K HDMI. So while there is plenty of bit depth of source data available, many chips doing 4K are struggling to have the clock rate to process so much data at such a high pixel clock, thus the chance someone in the chain may be dropping down below 4:4:4 to keep up.

We have 2-3 different models of 4K monitors in the office. One thing we could do is try to duplicate the same test and let you know results. If you have a particular test that would be useful for us to do, please let us know.

And if you can take the laptop around to connect with several monitors as you mentioned, those results may be useful to others if you’re willing to post them here.

Sorry I don’t have a quicker answer. Thanks for asking and for doing that separate digging,
Bernie


#3

Thanks for the detailed reply. A good test is the image in the first post. Just double-click it and it should appear unscaled on your screen.

Here are two monitor photos of a portion of the above image (taken with a cheap camera, sorry for the moiré effects). Both images are Plugable output. The first is from a Samsung 1920X1200 24-inch monitor. The magenta text is quite readable. The second is from the Changhong 3840x2160 42-inch monitor. I attempted to position the camera so both images are about the same size. (The pixels on the Changhong are 7/8 the size of those on the Samsung, in each dimension.)

!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275585/2k_inline.jpg?1442108425)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275585/2k.jpg?1442108425)
!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275587/4k_inline.jpg?1442108464)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1275587/4k.jpg?1442108464)

Please let me know how the test image looks on your test monitors. I hope to try a Vizio tomorrow and will post the result.

Thanks,

Stewart


#4

I tested a Vizio M43-C1 today and could not get readable magenta text, though it’s nowhere near as bad as the image below. I suspect that the screen glass confused my camera’s autofocus (it’s a cheap point-and-shoot with no manual focus option). However, by comparing magenta with grey, you can still see that there is a chroma subsampling issue.

We tried both the HDMI 2.0 and an HDMI 1.4 input, gaming mode on/off, and every relevant setting in the Picture and More Picture menus, all to no avail. I don’t know whether the Plugable adapter contributed to the problem.

I’m very interested in seeing the results with your test monitors.

Thanks,

Stewart

!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1276077/M43-C1_inline.jpg?1442200531)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1276077/M43-C1.jpg?1442200531)


#5

Hi Stewart,

I’ve run the chroma tests and the results look to be confirmation of 4:4:4 output from the UGA-4KHDMI adapter. On our Viewsonic VS 16024, the test pattern displays properly when running at 4Kp30. (In contrast, our Seiki 4K TV, which is certainly not 444 capable, clearly fails to display the test image properly.)

Viewsonic:
!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1281708/viewsonic_444_inline.jpg?1443056199)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1281708/viewsonic_444.jpg?1443056199)

Seiki:
!](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1281709/seiki_42x_inline.jpg?1443056219)](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1281709/seiki_42x.jpg?1443056219)


#6