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I’ve yet to see an LCD monitor with local dimming that I thought was any good. But I have now seen a DIY LCD display with an incredibly clever projector-based backlight solution that demonstrates why so-called HDR monitors with full-array local dimming are, in fact, complete crap.
Of course, it’s top-notch YouTube channel DIY Perks that’s responsible for this fantastic setup based on an ancient 11-year-old LCD TV and an even more elderly 14-year-old DLP projector. We’ve reported on some DIY Perks projects before, including this invisible PC built into a desk. But this new screen is my favourite.
To cut a long story short, what DIY Perks has done is to use an old DLP projector as a backlight, having dismantled an LCD TV to expose the rear of the panel. Essentially, you mirror the display output on the projector, fire that at the LCD panel as a backlight and—presto!—you have local dimming with the kind of precision that existing TVs and monitors can only dream of.
Now, I routinely complain about how bad local dimming is on monitors and TVs. A thousand or more dimming zones sounds like a lot. But the reality is that means a single zone is shared by thousands of pixels.
As DIY Perks also explains, even a screen with 2,584 dimming zones only has a backlight resolution of 68 by 38. Imagine how bad a monitor with a resolution of 68 by 38 would like. Quite.
Consequently, the backlighting doesn’t come close to the detail being displayed, resulting in halos and blooming around bright objects, plus the sections of the backlight visibly popping on and off. “I have a TV that uses this technology and I don’t like it at all,” says DIY Perks.
I agree, and then some. It looks totally rubbish. To be honest, I probably didn’t lean into the shortcomings hard enough when I review local dimming monitors like the Samsung Odyssey G9. In mitigation, you can turn off the dimming, which in fact is what I personally do.
Anyway, for this project, DIY perks used an old DLP projector with a mere XGA or 1,024 by 768 resolution. By modern screen standards, that’s fairly low. But it still effectively makes for 786,432 zones when used as a backlight. And it means for a 1080p screen, you’re only sharing a zone across just under three pixels on average.
Even for a 4K panel it would work out to about 10 pixels per zone, orders of magnitude better than the thousands of pixels per zone of any existing full-array dimming PC monitor we’ve reviewed.
Getting this all to work requires DIY Perks’ usual ingenuity. One neat detail is how removing the colour wheel from the projector massively boosts its brightness, which makes the difference between a hopeless dim display and one that’s bright enough to be impressive.
But the really clever bit is how DIY Perks uses a software tool called OBS to process the source image and create a luminance map. Without that, getting the image on the projector aligned to that on the LCD panel is just too difficult and creates some unavoidable visual artefacts.
With the luminance map the results are, well, stunning. Probably the most impressive single image is the comparison test of a TV with local dimming versus the DIY screen, both displaying a starfield (a real one, not the game).
The local dimming TV looks awful, with the panel all lit up between the individual dots and the border of the enabled backlight all too obvious and the field of stars progresses across the screen. It’s hideous.
By contrast, pun intended, the DIY Perks creation manages to light up only the dots or stars themselves. It looks fantastic. DIY Perks says that the overall brightness of the panel is possibly a bit lacking compared to a modern OLED display but that the results are still far, far preferable to conventional LCD panel, even with advanced local dimming.
There are a few unanswered questions left hanging. For instance, are there any challenges with syncing the DLP backlight with the LCD panel? But more than anything, this project just underlines how unsatisfactory existing local dimming technology is.
I already knew that. But seeing just how much better this DIY display is that technology you can buy really drives the point home. It also begs the question as to why commercially available tech isn’t better.
As it stands, existing local dimming tech feels like a checkbox exercise. It allows screen makers to claim they are selling a display with incredible dimming and therefore HDR capabilities which are true only in the very strictest sense. Were they actually trying to produce a great viewing experience, they’d be doing something much more similar to this DIY effort. Moreover, if a YouTube channel can produce something so much better than big tech companies, you know something has gone very wrong.
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Kurt Indovina
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