HDMI signals

Chroma subsampling

4:4:4, 4:2:2 and 4:2:0 explained

Every signal the Diva describes, on the OLED and in the web server, names its subsampling. It is usually the figure that explains why a link fits inside 18Gbps or does not.

A digital picture is normally carried as one luma channel, the brightness, and two chroma channels, the colour difference signals. The eye resolves fine brightness detail far better than fine colour detail, so the chroma channels can be sent at reduced resolution with very little visible loss. The three-number notation comes from analogue sampling practice and describes that reduction across a block two pixels high and four pixels wide.

4:4:4 sends a full colour sample for every pixel. 4:2:2 halves the chroma horizontally, so two neighbouring pixels share a colour sample. 4:2:0 halves it horizontally and vertically, so a block of four pixels shares one, which is what UHD Blu-ray and every streaming service uses because the video was encoded that way in the first place. RGB is 4:4:4 with no reduction at all. Bandwidth follows directly: at the same bit depth, 4:2:2 needs two thirds of what 4:4:4 needs, and 4:2:0 needs half.

Chroma subsampling on the HDfury Diva

The Diva reports subsampling everywhere it describes a signal. The OLED incoming line reads like 4K50 4:2:2 BT2020 12b LLDV 594MHz 2.2, and the INFO section shows an IN row and a VIDEO row for each output, so you can see at a glance whether the format changed on the way through.

You set it in two places, and they do different jobs. In the SCALER section, Custom Scaling offers a colour space list of Follow Input, which is the default, RGB FULL, RGB BT2020, 4:4:4 BT.709, 4:4:4 BT2020, 4:2:2 BT.709, 4:2:2 BT2020, 4:2:0 BT.709 and 4:2:0 BT2020, applied to the TX0 output when you click SEND. That changes what leaves the Diva. In the EDID section, the table handed to a source decides what it is willing to send in the first place: tables named 4K60-444 600MHz sit alongside 4K60-420 8-bit 300MHz ones, and FIXED EDID is deliberately a 4K60 4:2:0 8-bit 300MHz table, modest enough to produce a picture in almost any setup.

Choosing between them

The limit is the 600MHz, 18Gbps ceiling, and two different signals sit right on it: 4K60 4:4:4 8-bit and 4K60 4:2:2 12-bit. Both need a cable certified or tested for that bandwidth. Trading chroma for bit depth is therefore a real choice rather than a compromise, and on graded HDR material the extra bits are often worth more than the extra colour resolution.

One reported figure surprises people: any 4:2:2 signal is always processed at 12-bit and never clipped, which is why the Diva describes such signals as up to 12b even when the source is nominally 10-bit. Fine text and computer desktops are where 4:4:4 genuinely matters, since coloured text on a coloured background is the one thing subsampling visibly damages.

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