Kは1,000の単位。「1,000m = 1km」や「1,000g = 1kg」などと同じ。
ディスプレイでいう4K（=4,000）は「画像解像度の幅（ピクセル数）」
具体的には「3840×2160」の規格を指すことが多い（4000に満たないが）。
正式な国際標準規格は「Ultra HD(UHD)」
ITU-R BT.2100-1
| Parameter | Values |
| Image Container 1a Shape | 16:9 |
| Container Pixel count 1b
Horizontal × Vertical |
7 680 × 4 320
3 840 × 2 160 1 920 × 1 080 |
| Sampling lattice | Orthogonal |
| Pixel aspect ratio | 1:1 (square pixels) |
| Pixel addressing | Pixel ordering in each row is from left to right, and rows are ordered from top to bottom. |
| Frame frequency (Hz) | 120, 120/1.001,100, 60, 60/1.001, 50, 30, 30/1.001, 25, 24, 24/1.001 |
| Image Format | Progressive |
| NOTE 1a – Container is used to define the horizontal and vertical constraints of the image format.
NOTE 1b – Productions should use the highest resolution image format that is practical. It is recognized that in many cases high resolution productions will be down-sampled to lower resolution formats for distribution. It is known that producing in a higher resolution format, and then electronically down-sampling for distribution, yields superior quality than producing at the resolution used for distribution. |
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