Quick Note: Android Camera2 and External ISPs While weve - TopicsExpress



          

Quick Note: Android Camera2 and External ISPs While weve written about Androids Camera2 API before, there was one notable aspect of the discussion that was missing. The missing piece was a discussion of the physical link needed to enable all of the controls that were previously discussed. This isnt necessarily complicated, but it does represent a potential pitfall for updates to current devices. In short, the current protocols for using an external ISP provide insufficient bandwidth to support the full feature set needed for the new camera API. This means that some of the interesting features, such as per-frame controls are impossible to enable. As a result, many devices that weve evaluated before such as the Galaxy S4, HTC One (M7) and One (M8) wont support per-frame controls and similarly bandwidth-heavy features. The Galaxy Note 3, S5, and Note 4 appear to only use the on-die Qualcomm ISP. To understand why this is, we must understand the protocol that is used for communication. Today, the de facto standard for interfacing between the AP (application processor), ISP, and camera is MIPIs CSI protocol. By and large, CSI-1 and CSI-2 are the most common iterations of this protocol. While the transport protocol (D-PHY) that actually carries the images has immense amounts of bandwidth (up to 10 Gbps), the control protocol defined has almost no bandwidth in comparison. Instead, the control protocol relies on fast-mode i2c, which can only provide 400 kbit/s of bandwidth. While this may be an issue now, it seems that in the future this wont be an issue. According to Arrow Devices, the MIPI CSI-3 protocol merges control and transport protocols into a single M-PHY bus for up to 18.6 Gbps of bandwidth. Its likely that the demand for 4K60 video and 20+ megapixel burst mode functionality will drive adoption of this newer protocol. However, even now the disclosure of such protocols is rare, so its hard to say whether well see widespread adoption of CSI-3 any time soon. ift.tt/1tR3wLB
Posted on: Sun, 09 Nov 2014 22:18:54 +0000

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