Based on materials from android-softwares.com
The dual camera technology in a smartphone is no longer new. But now we are seeing a new trend emerging from manufacturers offering 'optical zoom' in their devices. For example, Apple ’s iPhone 7 Plus, and among devices on Android – OnePlus 5. Do all users know how this technology works? Let's try to figure it out …
Smartphone zoom problem
Before diving into the intricacies of the technology, it's worth explaining why manufacturers felt the need to add optical zoom to their smartphones. Unlike DSLR lenses with different focal lengths or 'point and shoot' zoom cameras, cameras in smartphones have small fixed focal length lenses. This means that you have only one option: use digital zoom to zoom in on a particular detail of the image.
But digital zoom is of very limited use – it doesn't make sense except in low magnification cases. We are bound by limitations in resolution and the field of view, which contains distant and near objects. That is, at a distance, a pixel can transmit only a limited amount of information. It is these constraints that give us a picture that decays into pixels when we use a zoom – it turns out that this is the same as simply enlarging an already finished frame from the gallery.
This macro shot compares 3x digital and 3x optical zoom (from 18mm to 55mm) in a shot with the same camera and the same settings
3x digital zoom: notice the increased noise and loss of detail on the cover
3x optical zoom: not only detail is preserved, but white balance is improved by focusing on the subject
A variety of lenses that come with DSLR cameras allow you to adjust the focal length and, accordingly, also the field of view. A larger focal length narrows the camera's field of view, but this means that the same sensor with a limited resolution transmits information from a smaller area, that is, each pixel transmits a smaller point on it. Therefore, optical zoom is not associated with pixelation problems, as is the case with digital zoom.
In order to evaluate the zoom of a camera or lens, we have to compare it with something, find a starting point. To determine the magnification, we divide the available focal length by the minimum possible. So an increase from 25mm to 50mm will be equal to 2x zoom, as will an increase from 18mm to 36mm. Magnification is a relative term, but it denotes a direct relationship between two focal length values.
Dual lens – hybrid solution
When it comes to dual-camera smartphones with a 'telephoto' lens, we mean two sensors and a pair of fixed lenses, but with different focal lengths. For example, one will have a 24mm focal length, the other 36mm, which potentially gives us a 1.5x optical zoom. Different sensors can vary in size, pixel size and aperture, which, of course, in turn affects the quality of photos taken with a particular camera.
For example, let's look at iPhone 7 Plus, in Apple they equipped it with one 28mm and one 56mm lens, that is, the device has a potential 2x zoom. This means we can take close-ups at 28mm 1x magnification and then just switch to a 56mm lens at 2x magnification and shoot farther away without any loss of quality.
And that is not all. The second camera also improves the quality of pictures taken at 4x and higher magnification. Since we already have a 2x zoom at full resolution initially, rather than a digital zoom from 1x, we only lose half of the information where we would normally lose three quarters at 4x. In other words, since we have a higher resolution for rendering distant objects, we won't get the same creepy pixelated images.
1x zoom on OnePlus 5
2x magnification on OnePlus 5
In the case of the OnePlus 5, the same story happens, it gives us 1.6x optical zoom on the second lens before cropping the image down to 20MP for 2x zoom and further software processing. OnePlus says it's part of the Smart Capture function, which gathers the information you want from different frames and then 'glues' the best parts together. Obviously, this is not the best approach, but such a hybrid solution is at least interesting. And even though the camera loses some of the data to achieve 2x magnification, the quality will still be better than if the old digital zoom method were used.
This dual camera not only allows you to get the best picture detail from a distance. It also enables advanced HDR processing, as is the case with other solutions with more than one camera. Even specific image details that were not captured in the final image, as well as additional light and shadow information, can be used to expand the dynamic range. The result is a photo that looks better regardless of the magnification applied.
Imperfect result
Surely you understand that the described solution is still far from perfect. We need digital zoom if we want to go beyond the maximum focal length, but what happens if we want to use an intermediate zoom level like 1.2, 1.3 or 1.5x?
The obvious solution is to use digital zoom for these lower magnifications, as the loss in quality will not be as noticeable in most conditions. As a result, it will be possible to switch to a fixed value of the optical zoom of the second camera, but this approach also has a disadvantage – a zoom level lower than the one we switch to will give the worst image quality.
So, for example, 1.1x to 1.6x could be a digital zoom with further switching to a second camera at 1.7x or more. This may explain why companies only offer modest zoom distances, the system still relies on digital zoom, and too far between the lenses will cause too much loss in quality.
A smarter implementation of this technology requires that there is no clearly laid down level at which switching occurs. The image processor can determine the noise level for each camera and whether to switch to the secondary camera – that is, whether it will give the best result. Apparently, both the iPhone 7 Plus and OnePlus 5 use something similar.
OnePlus's Smart Capture method, which combines data from many higher resolution images, is another step forward. By using multiple frames at a higher resolution, the noise level can be reduced to average by using intermediate magnifications such as 1.2 and 1.8x. However, this is technically possible with a camera with only one lens.
Simply switching between cameras is not an ideal solution, and the result is far from what smartphones advertise and cite 'optical zoom' among their advantages. It might make sense to resort to more powerful image analysis algorithms in order to combine the frames taken by both cameras. Unfortunately, there are also drawbacks here, comparable to those of real optical zoom lenses: the average and stitched picture is rarely as good as what we photograph.
Modern top-end processors are capable of combining data from cameras with different focal lengths. This is already being done for advanced HDR processing technologies, and the idea was further developed in the Light L16 multi-lens camera. This technical principle allows a high-resolution element to be taken from a high-magnification lens, cut and pasted into the center of the heavily magnified image. So, at 1.5x magnification, the center of the picture will contain more information, and the edges will be programmatically enlarged compared to the original result of shooting with a regular 1x lens. The result will be far from perfect, but the subject in the frame will look sharper and retain more detail compared to what it would look like in a photo taken with a conventional smartphone camera with one lens.
Assuming good lighting and strong noise reduction, the difference between 1X and 2X zoom on the OnePlus 5 is not great.
In low light conditions, both cameras obviously take very noisy shots, and there is no benefit from the dual camera as such
In theory, all this sounds simple enough, but in reality this algorithm requires significant processor resources, which means that much more time will pass between the shutter click and the final result on the screen. This is not well suited for fast-moving subjects or continuous shooting modes.
Worse, this type of image processing can only be further complicated by the different pixel sizes in the sensors and the different apertures in the dual camera, which will change the way light is used. Since a zoom camera does not collect enough light, as it usually has smaller pixels, the footage will be noisier, so stitching images will be simply pointless.
Based on the results we can see at this time, it doesn't seem like smartphone manufacturers have been able to achieve this level of sophistication. The closest technology available is perhaps what was done in Huawei – Hybrid Zoom, which takes accurate detail data from a 20MP camera and colors it using RGB data from a 12MP sensor, allowing larger 2x digital zoom.
As a result, the potential of the dual camera far exceeds what is visible at first glance, and it requires various complex processing technologies. Not to mention, the final result will ultimately depend on the shooting conditions.
Conclusion
While the dual camera is a significant step forward in mobile photography, there are still very noticeable pitfalls. The first problem is that even dual cameras are still limited to fixed focal lengths, which means they can't offer the same capabilities as true optical zoom – no matter what marketers tell us.
This technology has notable advantages over traditional digital zoom, including getting better quality photos when shooting at long distances. There is also a wider range of post-processing options available to you, including digital bokeh and advanced HDR processing. Let's not forget that these features offer photography enthusiasts more creative freedom.
The technology is still in the 'childish' stage and we will no doubt see noticeable improvements in camera quality and zoom functionality when the second generation of dual camera devices hits the market.
It would be interesting to know your opinion, dear readers. What do you think of the current state of the dual camera technology and the prospects for its development? Do you even consider the presence of a dual camera when choosing a smartphone?