A Closer Look at the G3's IR Laser Auto Focus System
by Joshua Ho on May 27, 2014 4:15 PM EST- Posted in
- Smartphones
- LG
- Mobile
- G3
Earlier today LG announced its 2014 flagship: the G3. Based on Qualcomm's Snapdragon 801, the G3 features a 5.5" 2560 x 1440 display and a host of other improvements over last year's G2. Although the front and rear facing cameras don't change in terms of resolution compared to the G2, the imaging system did see some upgrades. Optical Image Stabilization (OIS) is back for the G3, but it now includes stabilizing along the z-axis as well (hence OIS+). The big new feature however is the IR laser rangefinder that aids in improving focus time for the rear camera. LG claims the G3 can grab focus in 276ms. It's clear that the G3's AF system is one of the most interesting that I've seen in smartphone imaging, full stop. While PDAF (Phase Detect Auto Focus) is standard on dSLRs, laser rangefinders are generally rare and from another era.
While some guessed that this system was a method of assisting with auto focus by projecting a grid of lasers that would assist with detecting maximum contrast, LG uses accurate timing of emission vs reflection to determine the distance to a target. Looking at the IR window with an IR sensitive camera, the beam emitted is extremely thin in angle, much more focused than the average laser pointer. This means that the chance of multiple returns is greatly reduced compared to most situations.
LG emphasized the hybrid nature of its system, which explains how the G3 compensates for conditions where the laser auto focus fails. It appears that LG compensates for multiple returns, transparent and reflective surfaces with contrast-based AF detection as needed. LG also stated that the greatest benefit to the laser system is for nearly instant detection of distance to subject for the first two feet, and in cases where contrast detection is used the laser system allows the AF algorithm to automatically skip this distance to speed up focus. LG also says that the greatest benefit is seen in low light. I suspect that in outdoors situations the signal to noise ratio drops significantly. All of these claims will need verification, LG has definitely made a very interesting system for their camera, an interesting trade off between the larger sensor size and PDAF of the GS5 and the OIS+ and laser AF of the G3.
It's not quite clear how the laser AF is implemented in the software though. Based upon some casual inspection there is no clear reference to a laser or IR outside of TV. It is likely that the entire implementation is done through a single camera driver which obscures just how the rangefinder is treated. At any rate, all of this will require further investigation in a full review.
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Impulses - Tuesday, May 27, 2014 - link
And selfies perhaps? They also state it allows CDAF to skip the 2ft range tho, which might prove useful for other types of shots... If the laser detects all subjects are beyond 2ft then CDAF can skip right over that range, CDAF works by comparing contrast back and forth as it moves the AF point so shaving off a range from the comparison could speed it up under certain situations.What's the reason that CDAF for phones lags so far behind high end CDAF on mirrorless cameras anyway? I can understand point and shoots just don't have the processing power, but you'd think phones have way more processing than even high end M4/3 & NEX cameras... Or is it a function of sensor size that somehow allows for better CDAF?
The only thing PDAF (as used on DSLR) still does better is tracking, which is why Sony/Fuji/Olympus have gone with a hybrid approach that dedicates certain pixels to PDAF (but you can't have to many or the image suffers). Canon's gone with their new DualPixel tech on the 70D it seems, and Panasonic's developing a system that compares out of focus areas (GH4) using purely CDAF.
coburn_c - Tuesday, May 27, 2014 - link
Bingo.I imagine the bigger sensors in a proper DSLR let in more light and can therefore do finer contrast differentiation.
Impulses - Tuesday, May 27, 2014 - link
DSLR don't use CDAF tho, 'least not under most circumstances... But yeah, the sensor size of mirrorless APS-C & M4/3 cameras might be the reason CDAF is so fast there, although they used to be as slow as any P&S that also uses CDAF, they just refined it over time... So I'm not sure it's an inherent sensor size advantage.Wouldn't a larger sensor actually create less contrast in many situations tho? (specially when you open the lens up and have less depth of field) DSLR use CDAF with live view I think but they use a completely separate PDAF sensor that's nowhere near the image sensor (that's where part of the light reflected by the mirror goes).
PDAF has been refined for even longer since it goes back to SLR days... (pre-digital photography)
Impulses - Tuesday, May 27, 2014 - link
P.S. Where's Brian when you need him, he'd school us... :p In all seriousness, I'm sure he'd have some interesting commentary on this tho.hrrmph - Tuesday, May 27, 2014 - link
Early reports at PCMag are that it doesn't feel fast at all.melgross - Wednesday, May 28, 2014 - link
The biggest deal here is that this will assist indoors, where the light level is low. That's always the most difficult time a camera has. Outdoors, almost any focussing scheme will be fine, as long as the manufacturer does a proper job with it.