iPhone 6s vs. iPhone 6 and Galaxy S6: Camera Shootout

You may have an SLR at home, but chances are you don't carry it with you wherever you go. For quick snapshots when you're out and about, your smartphone is your camera.

But how can you be sure you're getting the best possible images out of your phone? That's a simple answer—spend $1,000 on an unlocked Panasonic CM1 ( at Amazon) , an Android phone that blows the competition out of the water by a very wide margin. But it's not the best handset out there, and most folks are going to opt for a Samsung Galaxy or an iPhone, depending on operating system preference.

We just got the new Apple iPhone 6s ( at Amazon)  in for testing today. I was able to wrestle the phone away from our cell phone guru Sascha Segan for about an hour to run some lab tests. I looked at the basics—sharpness, as well as image quality at low, middle, and high ISO sensitivities. Unique features, like Apple's Live Photos function, will be addressed in the forthcoming reviews of the 6s and 6s Plus.

Sharpness
The most basic test we run on cameras is a center-weighted sharpness test. We use an SFRPlus test chart and the Imatest software suite to analyze how well a lens performs. We look for an image to hit 1,800 lines per picture height using a center-weighted score (some lenses drop in resolution close to the edges of the frame), and also take a look to see if edges are problematic—with many point-and-shoot cameras that's the case.

The iPhone 6  and iPhone 6 Plus ($299.00 at Verizon)  share the same lens, a wide-angle with an f/2.2 aperture. The Galaxy S6 uses an f/1.9 lens that captures a little bit more light. That's not the only difference. The iPhones have image sensors with a traditional 4:3 native aspect ratio, the same as old standard definition TVs and most point and shoots. Samsung put a 16:9 aspect ratio sensor in the Galaxy S6, the same as an HDTV or modern widescreen computer monitor. That's a turnoff for serious photographers, who are used to composing images in a narrower frame.

See How We Test Digital Cameras

The Galaxy S6($84.55 at Amazon) has the highest sensor resolution of the trio—16 megapixels—but if you opt to capture images at a more traditional 4:3 ratio, the resolution is 11.9 megapixels. The left and right sides of the sensor get cropped. The iPhone 6 and 6 Plus share the same 8-megapixel image sensor, and the new iPhone 6s and 6s Plus both use a 12-megapixel image sensor. The extra resolution is required for 4K video—in the case of the iPhone's 4K capture mode, the top and bottom of the frame are cut off, as opposed to the S6 which uses its entire sensor to capture 4K footage. The iPhone 6's video recording tops out at 1080p.

Imatest tells us that, of the three phones, the iPhone 6s delivers the sharpest images. It scores 1,874 lines on the center-weighted test. The center and mid parts of the frame are crisp, but the outer third does show some softness (1,500 lines). The iPhone 6 Plus isn't that far behind, notching 1,839 lines on the test; its edge quality is actually a bit better at 1,703 lines. Sample variation may play a part in terms of pure image quality, but one thing that's clear is that the lens on the new iPhone doesn't resolve quite enough detail to take advantage of its high-resolution sensor. Even though it packs more pixels than its predecessor, the advantages in detail are relatively slight. Keep in mind that, because of the strength of our lights in our resolution scene, the iPhones defaulted to a virtual ISO of 250—at lower ISOs the scores would be higher.

The Galaxy S6 has the weakest sharpness score of the trio. It scores 1,453 lines on the sharpness test, which is less than what we want to see in a photo. Its edges are quite soft when shooting at 16:9, so if you shoot at 4:3, images will have more apparent sharpness. But even so, the center parts of the image show just 1,530 lines. Galaxy resolution tests were performed at ISO 100, its lowest sensitivity.

One other issue with the wide image sensor—if you shoot at 16:9 the Galaxy S6 captures just as wide a field of view as the iPhone from a horizontal perspective, but is much tighter vertically. When cropping Galaxy images to 4:3 the iPhone has an advantage with wide-angle shots—it captures more of the scene.

ISO Performance
Apple doesn't support manual ISO control, which makes testing image quality at set sensitivities a challenge. We do use variable power lights in our testing lab, but are at the mercy of the camera app as to which ISO it chooses. Couple that with the fact that the iPhone models have much lower base sensitivities—the 6s' sensor starts at ISO 25, the 6 and 6 Plus at ISO 32, and the Galaxy S6 at ISO 100—it makes for a bit of a tough comparison.

From left to right: iPhone 6s, iPhone 6 Plus, Samsung Galaxy S6. The iPhone 6 and 6 Plus have the same still image quality.

In bright light—outdoors, even on a cloudy day—your phone is going to default to its lowest ISO. So I compared a shot from each model at its base ISO. Noise isn't an issue with any of the three—they all show between 0.7 and 0.8 percent, which is well below the 1.5 percent that we find troublesome—and all three cameras show a solid amount of detail, more than ample for Web sharing.

The crop is taken from our ISO test scene, from a portion of the shot toward the right side of the frame. This is why the trees in the image, at the far right of the crop, are downright blurry in the S6 image when compared with the iPhone shots. That won't be an issue when shooting or cropping a 4:3 ratio, but is certainly a concern when shooting video.

From left to right: iPhone 6s, iPhone 6 Plus, Samsung Galaxy S6

At moderate ISOs—ISO 500 for the iPhones and ISO 400 for the Galaxy—the story is dramatically different. The extra pixels crammed into the iPhone 6s sensor come into play, and details are blurred. The iPhone 6 Plus does a better job resolving detail, but it's the Galaxy S6 that shines—with the exception of the left and right sides of a 16:9 frame, which are going to be blurry regardless of ISO.

From left to right: iPhone 6s, iPhone 6 Plus, Samsung Galaxy S6

And when you move to top sensitivities—ISO 800 for the 6s and S6, and ISO 640 for the 6 Plus—none of the results are that great, but the Galaxy S6 holds up the best. Even with our lights at the lowest power, the iPhone 6 Plus wouldn't move beyond ISO 640.

Conclusions
If you want to buy the phone with the best integrated camera, without regard to other factors, your choice is clear. Get the Panasonic CM1. But if you're looking for a more mainstream, balanced handset, you're going to look hard at the top offerings from Apple and Samsung. Operating system bias aside—Android fans will be Android fans and iOS fans will be iOS fans after all—it depends on what type of photography you want your phone to do. If you're only concerned about outdoor shots, and love shooting wide angles at a traditional aspect ratio, either iPhone will serve you well. But who only captures images outdoors during the day? If you're like most of us, the Galaxy S6 is a better all-arounder, even if its edges show some serious blur at 16:9.

If you're a serious shutterbug, carry a camera with Wi-Fi—a premium pocket model like the Sony RX100 III ($748.00 at Amazon) will outlast your phone and absolutely murder it in regards to image quality—and use that for social sharing. And just pick whichever phone is best for you in other ways.