A new benchmark for taking photos with domestic mobile phones? Comprehensive analysis of Sony IMX400

It 168 MWC 2065 438+07 evaluation, Sony won this year's MWC best mobile phone award for its mobile phone Xperia XZ Premium. As Sony's new flagship, it has many bright spots, including the first Qualcomm Xiaolong 835 chip, full mirror body shell, 4K HDR display and the first IMX400 photosensitive element. Design, image and display have always been Sony's traditional strengths, and this time it was vividly displayed on Sony Xperia XZ Premium.

Also released with Sony Xperia XZ Premium is Sony Xperia XZs. It is also equipped with IMX400 photosensitive elements, which is a great improvement point compared with the previous generation XZ. The reason why I always emphasize this brand-new photosensitive element is that it will affect the camera performance trend of the flagship mobile phone made in China this year.

According to the performance of Sony in the third quarter of fiscal year 20 16, the operating profit of Sony's semiconductor business reached 27.2 billion yen, ranking fourth among the nine major businesses of the group, even surpassing the home entertainment and audio business and mobile communication business. The reason why Sony Semiconductor has such a bright performance is that the number of image sensors sold has increased greatly. This is closely related to the fact that mobile phone manufacturers are equipped with Sony image sensors. Every time Sony releases a new sensor, it naturally becomes the object that domestic mobile phone manufacturers are scrambling to adapt.

In fact, as early as February 7 this year, Sony has announced the IMX400 photosensitive element to the public. According to Sony's official explanation, the traditional double-layer CMOS image sensor consists of a back-illuminated pixel layer and a signal processing circuit layer with a pre-installed circuit chip, while the new CMOS image sensor has a new DRAM layer between these two circuits. Simply put, Sony packaged a memory into CMOS, which enabled IMX400 to exchange image data more quickly.

▲ Traditional double-layer stacked CMOS image sensor

▲ Newly developed 3-layer stacked CMOS image sensor with DRAM layer.

From the comparison above, I can clearly see that the DRAM layer is located between the pixel module and the circuit module. When the pixel module obtains the image information, it will be transmitted to DRAM for short-term storage, and then the image information will be processed by the circuit module, and the DRAM layer plays a buffering role.

The sensor with DRAM layer has derived two characteristics, that is, it can capture the still image with minimum distortion of objects in high-speed motion and shoot ultra-slow motion video. Let's interpret them one by one.

Anti-distortion shooting

According to Sony's official demonstration, the new sensor can read the still image of1120 seconds (about 4 times faster than the traditional product) with the help of the high-speed, low-energy and large-capacity DRAM in the stacked structure, and at the same time can reduce the delay of reading each pixel. This technology of keeping the focal plane distortion of static images to the lowest level may be applied to smartphones that lack mechanical shutters to control exposure time, helping them to take images of fast moving objects.

In other words, photos that used to take 1/30 seconds can now be taken in1120 seconds. So what is the application point of this in the actual use process? First of all, CMOS with DRAM layer has a wider range of shutter time adjustment, and professional photographers can adjust their own shutter time more freely. Secondly, the faster the shutter is, the more leisurely it is to take pictures of moving objects, or the less likely it is to have residual images or deformation when shooting moving objects.

▲ Reading speed 1/30 seconds shooting effect.

From the comparison chart, we can intuitively see that at the reading speed of 1/30 seconds, the front of the photo is tilted to the right, while at the reading speed of1120 seconds, the front of the photo maintains a normal image. It can be seen that IMX400 CMOS anti-distortion performance is immediate.

▲ Reading speed1120 seconds.

Super slow motion video shooting

Before CMOS with DRAM layer appeared, at present, all mobile phones supported the maximum slow-motion video shooting of 240fps. However, according to the parameters of IMX400, it can shoot 1000fps video in full HD (1920x 1080 pixels) mode, which is about 8 times that of traditional CMOS, which means it is 8 times slower than the slow-motion video you shoot with iPhone7, which is obviously very exaggerated.

▲ Cross-sectional view of 3-layer stacked CMOS image sensor equipped with DRAM

It is worth mentioning that when users shoot videos, normal speed videos and ultra-slow motion videos can be seamlessly connected. CMOS can automatically detect that the object suddenly starts to move, and immediately start the high-speed photography mode. This is because high-speed shooting data can be temporarily stored in DRAM, while normal shooting mode can bypass DRAM and be directly processed on ISP.

After technical analysis, let's take a look at the photo performance of Sony Xperia XZ Premium equipped with IMX400 processor. However, it should be noted that the following samples and videos are all from the engineering machine of Sony Xperia XZ Premium, and the performance in all aspects may be different from the production version.

Judging from these three proofs, the imaging performance of Sony Xperia XZ Premium is better than that of Bisogni Xperia XZ. Previously, the serious tailing phenomenon of Sony Xperia XZ photos has been significantly improved, and the clarity of the photos is very high, and it also has a good performance in the case of insufficient indoor light. However, as far as personal perception is concerned, the photos taken by this mobile phone always have a feeling of underexposure. Perhaps Sony will adjust the imaging software algorithm later. In addition, the video anti-shake and triple sensor on Sony Xperia XZ are still inherited. Since Sony Xperia XZ Premium has not yet been sold, there are not many samples taken at present. I will wait until the real machine comes out to test.

It is worth mentioning that the rear camera of Sony Xperia XZ Premium supports the MOTION EYE shooting system and has the front shooting function. In other words, it can keep three frames of photos in a short time before the user presses the shutter, and it can be selected by the user after the photo is taken, making it easier for the user to capture the desired moment. You might say that Apple's Live Photos is no better than it, and it can shoot short videos, while Sony can only shoot three. In fact, the IMX400 sensor can pre-record the image before the shutter is pressed through the DRAM layer. The photos it records are all full-pixel still photos, while Apple is just a short video with low fps and low resolution.

Is it cool to watch 960fps slow-motion video? . . In fact, as long as we pay a little attention, there are many scenes in life that can be filmed in slow motion. For example, the moment of taking a male ticket; The moment when pets run and play; The moment the dandelion was blown away, and so on. Adding slow motion will make the video look like a blockbuster.

To sum up, the highlight of Sony IMX400 CMOS is to package DRAM into CMOS, which can be used as a data buffer to record image information in advance. The whole CMOS prediction technology, slow-motion shooting and snapshot experience have been qualitatively improved. However, according to the information revealed by Zackbus in Weibo, although Sony officially claims that DRAM layer is high-speed, low-power and large-capacity, it will inevitably increase power consumption compared with traditional CMOS. Therefore, the battery life of the mobile phone and the fever of the camera module may be a hidden problem.