As described in the previous article, the application of dual cameras is mainly divided into: distance-related applications, optical zoom, dark light compensation, and 3D shooting and modeling. The principle of each application is different, we will introduce the relevant principles separately:
Distance related application
The human eye is very easy to locate the distance of an object, but when one closes one of the eyes, the positioning ability will drop a lot.
The dual camera is an application that simulates the human eye.
To put it simply, if the distance is measured, it is calculated by the algorithm that the angles θ1 and θ2 of the object and the left/right camera, plus the fixed y value (ie the center distance between the two cameras), it is very easy to calculate the z value. (ie the distance from the object to the Camera)
However, it is easy to calculate that if the distance between the two cameras is too small, the distance of the calculated object will be very close. If you want to calculate a long distance, you must extend the distance between the left and right cameras.
optical zoom
The optical zoom mainly uses different FOVs (viewing angles) for the left and right cameras, so that the two cameras are different in viewfinder. When the user needs a wide-angle photo, the left camera is framing with a viewing angle of 85 degrees to obtain a wide-angle effect. When the user needs a telephoto photo, the right camera is framing with a viewing angle of 45 degrees to obtain a telephoto effect.
In order to make the objects captured by the left and right cameras have a high degree of overlap, the optical zoom dual camera module cannot be as large as the module of the camera to be applied, but the closer the left and right cameras are, the better.
Dark light enhancement
In fact, in the second part, Xiaobian has briefly introduced the principle of dark light enhancement. Generally speaking, the dark light enhancement is to use two cameras with a standard camera of RGBG and a black and white camera with RGBG filters removed. RGBG is used to obtain the color of the object, while the black and white camera is used to obtain a better amount of light to determine the intensity of the object being shot. Then combine the two images to get a better dim enhancement.
In general, there are two ways to integrate:
1. With black and white pictures as the main body, paste the color of each pixel obtained on the color picture onto the black and white picture to fuse the two pictures.
2. With the color picture as the main body, the brightness intensity of each image obtained on the black and white picture is compensated to the color photo, and the two pictures are merged.
As for which method is more suitable for integration, it may be that the benevolent sees the wise and sees wisdom, and does not discuss it here.
Similarly, to make dark light enhancement, in order to make the objects captured by the left and right cameras overlap, such dual camera modules are also required to be as close as possible.
What needs to be explained, Huawei P9 actually uses the module of this mode.
Of course, some insiders also said that the current effect of this algorithm is not obvious. Dark light compensation is really helpful for users, especially when shooting night scenes. However, some customers think that Sony and Samsung's Dual PD technology is very good, and prefer to use the Dual PD camera for dimming compensation.
In the end, whether it is a dual camera or a dual PD, the dark light compensation effect is good. You can compare the Huawei P9 and Samsung's Galaxy S7 edge, and you will have an answer.
3D shooting and 3D modeling
The algorithm of 3D shooting and 3D modeling is actually similar to the distance application, but its accuracy requirements are higher, and sometimes it is necessary to use infrared ranging for more accurate distance judgment. The small series here will not be introduced in detail.
Requirements for ISP
When it comes to the algorithm of dual camera, I have to mention ISP (Image Signal Processing). The main function of ISP is to post-process the signal output from the front-end image sensor. The main functions are linear correction, noise removal, and dead point removal. Interpolation, white balance, automatic exposure control, etc., rely on ISP to better restore the scene details under different optical conditions. ISP technology largely determines the imaging quality of mobile phones.
In the era of feature machines, ISPs are all made on the camera, and different pixel cameras are equipped with different performance ISPs. As the pixel of the mobile phone camera is getting higher and higher, the requirements for ISP performance are getting higher and higher. If the ISP is integrated into the camera sensor, the module of the camera will be too large, and even affect the photographing effect. So in the era of smart phones, ISPs are generally on the main chip SoC. In order to achieve better results, some brand customers even cost an extra ISP to achieve better and more professional photo effects.
A good camera algorithm needs to be matched with a good ISP. The ISP and the algorithm complement each other and are indispensable. The dual camera requires more ISP performance. First of all, in order to enable the signals of the left and right cameras to be processed at the same time, a single ISP can no longer meet the needs of dual cameras. This requires a dual ISP to implement this feature.
Taking dark light enhancement as an example, the color/black and white images enter their respective ISP channels and calibration channels, and then match the two pictures (such as extracting the same part of the two pictures and removing the part captured by only one camera). The relevant pictures are then processed by algorithms such as occlusion, detection, and compensation. Finally, the two images are merged to achieve color enhancement. Of course, in fact, the ISP cooperates with the algorithm to do more than the picture. Xiaobian really doesn't know, it's not here to mislead everyone.
Of course, there is also a small episode in it. After all, there are two ISPs. The two ISPs have some processing speeds and different processing capabilities. In order to ensure that the two ISPs can sample at the same time, the pictures taken by the dual cameras need to be taken at the same time. One solution is to have the Sensor have a sync signal pin. The synchronization signals of the two cameras are docked, and each time the picture is read, the pictures are all time stamped, and the ISP uses the time stamp to ensure that the photos taken by the left and right cameras are taken at the same time, and finally merged.
Camera interface
In general, the camera interface of current smartphones is a MIPI interface. Previously, the mobile phone platform only had 2 MIPI interfaces, which were given to the front camera and the rear camera respectively. To do a dual camera, the platform is required to support at least three MIPI interfaces. In fact, on the previous high-end platform, in order to achieve higher pixels, two-way ISP has been used (for example, to support a 16M camera, two-way 8M-capable ISPs will be used), and such platforms are likely to have only two MIPIs. But this can't stop the engineer from doing the front camera + rear dual camera.
That's right, with a little Swtich, you can easily implement a dual camera.
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