1 <html devsite> 2 <head> 3 <title>Metadata and Controls</title> 4 <meta name="project_path" value="/_project.yaml" /> 5 <meta name="book_path" value="/_book.yaml" /> 6 </head> 7 <body> 8 <!-- 9 Copyright 2017 The Android Open Source Project 10 11 Licensed under the Apache License, Version 2.0 (the "License"); 12 you may not use this file except in compliance with the License. 13 You may obtain a copy of the License at 14 15 http://www.apache.org/licenses/LICENSE-2.0 16 17 Unless required by applicable law or agreed to in writing, software 18 distributed under the License is distributed on an "AS IS" BASIS, 19 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 20 See the License for the specific language governing permissions and 21 limitations under the License. 22 --> 23 24 25 26 <h2 id="metadata">Metadata support</h2> 27 <p> To support the saving of raw image files by the Android framework, substantial 28 metadata is required about the sensor's characteristics. This includes 29 information such as color spaces and lens shading functions.</p> 30 <p>Most of this information is a static property of the camera subsystem and can 31 therefore be queried before configuring any output pipelines or submitting any 32 requests. The new camera APIs greatly expand the information provided by the 33 getCameraInfo() method to provide this information to the application.</p> 34 <p>In addition, manual control of the camera subsystem requires feedback from the 35 assorted devices about their current state, and the actual parameters used in 36 capturing a given frame. The actual values of the controls (exposure time, frame 37 duration, and sensitivity) as actually used by the hardware must be included in 38 the output metadata. This is essential so that applications know when either 39 clamping or rounding took place, and so that the application can compensate for 40 the real settings used for image capture.</p> 41 <p>For example, if an application sets frame duration to 0 in a request, the HAL 42 must clamp the frame duration to the real minimum frame duration for that 43 request, and report that clamped minimum duration in the output result metadata.</p> 44 <p>So if an application needs to implement a custom 3A routine (for example, to 45 properly meter for an HDR burst), it needs to know the settings used to capture 46 the latest set of results it has received in order to update the settings for 47 the next request. Therefore, the new camera API adds a substantial amount of 48 dynamic metadata to each captured frame. This includes the requested and actual 49 parameters used for the capture, as well as additional per-frame metadata such 50 as timestamps and statistics generator output.</p> 51 <h2 id="per-setting">Per-setting control</h2> 52 <p> For most settings, the expectation is that they can be changed every frame, 53 without introducing significant stutter or delay to the output frame stream. 54 Ideally, the output frame rate should solely be controlled by the capture 55 request's frame duration field, and be independent of any changes to processing 56 blocks' configuration. In reality, some specific controls are known to be slow 57 to change; these include the output resolution and output format of the camera 58 pipeline, as well as controls that affect physical devices, such as lens focus 59 distance. The exact requirements for each control set are detailed later.</p> 60 <h2 id="raw-sensor">Raw sensor data support</h2> 61 <p>In addition to the pixel formats supported by 62 the old API, the new API adds a requirement for support for raw sensor data 63 (Bayer RAW), both for advanced camera applications as well as to support raw 64 image files.</p> 65 66 </body> 67 </html> 68
