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How LG uses fuzzy math to label some of its LCD TVs as 4K

Jon L. Jacobi | Sept. 22, 2016
By replacing every fourth red, green, or blue subpixel with a white one, LG boosts the brightness of its 6100-, 6500-, and 6800-series models. The trick works, but it sacrifices resolution.

Here we see the offset replacement RGBW pattern that LG uses in its budget LCD TVs.There are still 11,520 subpixels and 3840 whole pixels per line, but only 2880 of those whole pixels can produce the full range of colors (because every fourth subpixel is white).

The RGBW pixels in LG’s OLED TVs

oled rgb

When building its OLED TVs, LG uses four subpixels (red, green, blue, and white) to create one whole pixel. That’s 15,360 subpixels and 3840 pixels per row.

Note that the above images are to illustrate a concept; they’re not necessarily indicative of the way the subpixels or pixels are sized, spaced, or oriented. The black borders in the illustration are there simply to divide the pixels.

If you count the number of red, green, and blue subpixels, you’ll see where the math goes wrong for LG’s RGBW LCD TVS:

  • 4K RGB LCD: 11,520 subpixels in groups of red, green, and blue, forming 3840 RGB pixels per row.
  • LG’s 4K RGBW OLED: 15,360 subpixels in groups of red, green, blue, and white, forming 3840 RGBW pixels per row
  • LG’s RGBW LCD: 11,520 subpixels where only some groups have all three color elements. Every fourth red, green, or blue subpixel is replaced by a white subpixel to increase luminance. That still comes out to 3840 pixels per row, but there are only 2880 RGB groups staggered over those 3840 pixels.

LG defends the marketing of these RGBW LCD models as 4K TVs, rightly stating that they have 2160 horizontal rows with 3840 pixels consisting of three subpixels each. This forms a matrix of 8,294,400 distinct areas of luminance, and the ISO (International Standards Organization) is big on luminance, a fact that LG is quick to point out in this promotional video available on YouTube:

Where LG’s argument falls apart is in the reduced number and increased spacing of the red, green, and blue subpixels. It’s simply not possible to render details as finely with LG’s matrix—where every fourth red, green, or blue subpixel is replaced by white—as other 4K TVs can render with matrices consisting of conventional RGB (or RGBW) subpixel groupings.

LG mitigates this shortcoming somewhat by tweaking how individual subpixels are addressed and by offsetting subpixel colors by row, so that two white subpixels are never adjacent. But at the end of the day, the LG panels in question still have only 75 percent of the red, green, and blue subpixels to work with.

To the test

To empirically test whether LG’s panels fall short on 4K image quality, I gathered up my 4K (3840x2160) test files, and headed for the local big-box store. I would have loved to sit in the lab comparing TVs, but I was unable to obtain a relevant TV from LG in time. No matter, though. The results on the LG 6100-series TVs I saw were indicative of an image-quality deficiency compared to 4K UHD. In fact, they were obvious upon close inspection to both myself and everyone around me.

 

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