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4K DLP Projectors -- is the chip really 4K?

4K DLP Projectors :
Is the 4K DLP Chip really 4K?

Evan Powell, January 23, 2017
ProjectorCentral.com

4K DLP projectors featuring TI's new 4K UHD DLP chip are in the news, especially with the Optoma UHD60 coming to market late in the second quarter at the surprisingly low price of $2,799.

But is the new 4K DLP chip really a genuine native 4K chip? After all, it has only 4.15 million mirrors, not the 8.3 million that is required for native 4K 3840x2160 display. Is it doing pixel shift in the same way that the 3LCD 4K enhanced projectors from Epson and JVC are doing?

The answer is yes and no. The similarities are these: They both rely upon an optical diagonal off-shifting of the pixels on sequential refreshes so that there is a partial overlapping of the pixels on the second pass. So a base image and an off-shifted image are both displayed for each frame. This happens so fast that the eye blends them into one image. As you are watching a movie there is no awareness that this is going on.

4K projectors using either the 4K DLP chip or the 4K-enhanced 3LCD process will accept native 4K signals and then apply some extensive video processing on these signals to prepare them for output to their non-native DLP or 3LCD imaging devices. The difference is that TI's 4K UHD process produces independent single-pixel structures, whereas the 3LCD process does not.

Practically speaking, the most obvious difference between the 4K DLP and 4K-enhanced 3LCD projectors is apparent resolution. The 4K-enhanced 3LCD projectors from Epson and JVC (those currently on the market at any rate) use native HD 1080p chips which are 1920x1080 in physical resolution. Resolution enhancement is achieved by projecting a 1920x1080 image on the first scan, then on the next refresh of the chips a second 1920x1080 image is off-shifted diagonally and overlaid onto the first scan. The total number of addressable pixels in this process is (1920x1080) x 2 = 4.15 million, which is half of the 8.3 million in a native 4K signal.

The 4K DLP chip starts with double the resolution of the 3LCD devices. It has a total of 2716x1528 mirrors. Through some proprietary video processing it is able to deliver two discrete pixels for each mirror. When using this chip in the pixel-shifting process, it delivers double the number of pixels in each refresh compared to the 3LCD projectors. The total number of addressable pixels in this process is (2716x1528) x 2 = 8.3 million, or the same as a native 4K signal. The pixels have been reformulated through video processing to map the native 4K signal information onto this pixel shifted delivery mechanism.

So what do they look like?

The result of both of these processes, as far as the eye perceives, is substantially enhanced picture resolution compared to standard HD 1080p. As far as 3LCD is concerned, though the math says it is half the number of addressable pixels compared to native 4K, from a typical viewing distance the eye will perceive video material displayed on 4K-enhanced 3LCD projectors as much closer to native 4K than 1080p--subjectively the picture does not look like it is "half way" in between 1080p and 4K as the math would suggest. It looks more like it is about 90% native 4K, at least with video subject matter. The bottom line is that when viewing video material from normal viewing distances it will be difficult for most consumers to tell the difference in resolution between a picture produced by a projector using native 4K chips and one using the 3LCD pixel-shift technology.

However, when you switch to something other than video you get a different impression. For example, when you are projecting high resolution graphics or densely packed financial spreadsheets in small fonts, the latent resolution strength of the 4K DLP chip compared to 3LCD pixel-shift becomes much more apparent. When viewing this type of subject matter on 3LCD pixel-shifted projectors, you may tend to see moire patterns in complex graphics, or soft, imprecise resolution of the serifs on small text on a spreadsheet. These details are more acutely resolved with native 4K projectors, or with projectors using the new 4K DLP chip.

Now, with the new 4K DLP chip, the math says that since the physical resolution is doubled as compared to 3LCD, that should push the subjective results on the screen from a perceived (say) 90% of 4K to a potential of 95% 4K. However, once again the math is misleading. This is not what happens. The detail resolution produced by the 4K DLP chip is for all practical purposes indistinguishable from pure native 4K, even when examined from very close up. The ultimate test of this is the display of a 4K resolution 1-pixel line test pattern which contains alternating black and white lines that are each one pixel wide. When viewing this test pattern on a projector using the 4K DLP chip, each line is clean and clearly defined, and you see distinct pixel definition when examining it up close. It is not possible to achieve this level of precision using the pixel shift technology with standard HD 1080p chips.

Therefore, despite the fact that the 4K DLP chip itself has 4.15 million mirrors instead of 8.3 million, we have no problem categorizing the 4K projectors using this chip as native 4K resolution based on the fact that they can display a clean 1-pixel line test pattern. No native 4K projector can do any better. Practically speaking, the number of mirrors on the chip is irrelevant if it can put 8.3 million discrete pixels on the screen and fully resolve a 4K 1-pixel line pattern.

Other vital factors to consider

3-chip convergence.One other contributing factor to the resolution power of the 4K DLP chip is that in its single-chip implementations (using a color wheel as light modulator), there is no risk of a convergence issue as there may be on any three-chip light engine design, whether DLP, 3LCD or LCOS. With 4K resolution, the precise convergence of three independent red, green, and blue imaging chips becomes vital when it comes to maximizing image definition. The latent advantage of sequential color updates from a single DLP chip is that all three colors are always in perfect convergence. So oddly enough, the single 4K DLP chip used with a color wheel has the potential to deliver slightly more precision than a true native 4K projector that uses three separate chips for R, G, and B, if those three chips are not in perfect alignment.

Viewing distance. It is also important to keep in mind that viewing distance is a huge factor in perceiving resolution. As it is, when viewed from a common distance of (say) 1.3x the screen width, you cannot see all the detail on the screen even in a standard 1080p image. Move up close and you can see pixel structure, but move back to that viewing distance and that pixel structure disappears because it is beyond the ability of the human eye to resolve that tiny detail. Now, a picture generated by either the 4K DLP chip, or by the 3LCD 4K-enhanced models, will certainly appear higher in resolution than a standard HD 1080p picture from a distance of 1.3x the screen width. But since we are reaching the limit of the human eye to resolve fine detail at this distance, the perceived differences between native 4K and the 3LCD 4K-enhanced projectors become subtle with video, although as noted previously, less subtle with high resolution graphics and text.

Contrast. The subjective impression of a picture's resolution is determined in significant part not by actual physical resolution but by the contrast of the image -- the higher the contrast, the higher the picture's resolution will appear to be to you. That is because details in shadows and highlights stand out more clearly on a high contrast projector, and edges between dark and light objects appear to be more acutely defined. Due to this phenomenon, when you factor in normal viewing distance, it is possible that a very high contrast conventional HD 1080p projector could appear to be higher in resolution than a native 4K projector with lower contrast. This is why many videophiles would argue that high contrast (along with other factors like color accuracy and wide color gamut) are actually more critical components to a successful image than resolution, especially when it comes to home theater projectors.

Conclusion

In the end we urge you to consider ALL aspects of a projector's capabilities and attributes before making a buying decision. 4K resolution is obviously a hot ticket in the projector world these days, and we would argue that the new 4K projectors featuring TI's 4K DLP chip qualify as native 4K based on the acute precision of the image on the screen, and the ability of each mirror to drive two independent single pixel structures. How they do that is related to some behind-the-scenes technological magic (proprietary to TI) that you will never be aware of.

Nevertheless, as impressive as the high precision 4K DLP chip is, that precision is more apparent with complex graphics and dense text than it is with video. But this is true of ALL projectors using native 4K chips, not just the new 4K DLP chip. In the end, your subject matter itself as well as your preferred viewing distance will determine how much detail is actually visible on the screen. Keep these things in mind as you check out all of the exciting options you have for upgrading to a new 4K projector.


(12/18/17 - 04:53 AM PST)
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