Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 1 | page.title=Camera HAL v3 overview |
| 2 | @jd:body |
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| 19 | <div id="qv-wrapper"> |
| 20 | <div id="qv"> |
| 21 | <h2>In this document</h2> |
| 22 | <ol id="auto-toc"> |
| 23 | </ol> |
| 24 | </div> |
| 25 | </div> |
| 26 | |
| 27 | <p> |
| 28 | Android's camera Hardware Abstraction Layer (HAL) connects the higher level |
| 29 | camera framework APIs in |
| 30 | <a |
| 31 | href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a> |
| 32 | to your underlying camera driver and hardware. The latest version of Android |
| 33 | introduces a new, underlying implementation of the camera stack. If you have |
| 34 | previously developed a camera HAL module and driver for other versions of |
| 35 | Android, be aware that there are significant changes in the camera pipeline.</p> |
| 36 | <p>Version 1 of the camera HAL is still supported for future releases of Android |
| 37 | because many devices still rely on it. Implementing both HALs is also supported |
| 38 | by the Android camera service, which is useful when you want to support a less |
| 39 | capable front-facing camera with version 1 of the HAL and a more advanced |
| 40 | back-facing camera with version 3 of the HAL. Version 2 was a stepping stone to |
| 41 | version 3 and is not supported.</p> |
Clay Murphy | 594d0ed | 2014-10-21 11:04:30 -0700 | [diff] [blame^] | 42 | |
Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 43 | <p> |
| 44 | There is only one camera HAL module (with its own version number, currently 1, 2, |
| 45 | or 2.1), which lists multiple independent camera devices that each have |
| 46 | their own version. Camera module v2 or newer is required to support devices v2 or newer, and such |
| 47 | camera modules can have a mix of camera device versions. This is what we mean |
Clay Murphy | 594d0ed | 2014-10-21 11:04:30 -0700 | [diff] [blame^] | 48 | when we say Android supports implementing both HALs. |
Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 49 | </p> |
Clay Murphy | 594d0ed | 2014-10-21 11:04:30 -0700 | [diff] [blame^] | 50 | |
| 51 | <p class="note"><strong>Note:</strong> The new camera HAL is in active |
| 52 | development and can change at any time. This document describes at a high level |
| 53 | the design of the camera subsystem and omits many details. See <a |
| 54 | href="versioning.html">Camera version support</a> for our plans.</p> |
Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 55 | |
| 56 | <h2 id="overview">Overview</h2> |
| 57 | |
| 58 | <p> |
| 59 | Version 1 of the camera subsystem was designed as a black box with high-level |
| 60 | controls. Roughly speaking, the old subsystem has three operating modes:</p> |
| 61 | |
| 62 | <ul> |
| 63 | <li>Preview</li> |
| 64 | <li>Video Record</li> |
| 65 | <li>Still Capture</li> |
| 66 | </ul> |
| 67 | |
| 68 | <p>Each mode has slightly different and overlapping capabilities. This made it hard |
| 69 | to implement new types of features, such as burst mode, since it would fall |
| 70 | between two of these modes.<br/> |
| 71 | <img src="images/camera_block.png" alt="Camera block diagram"/><br/> |
| 72 | <strong>Figure 1.</strong> Camera components</p> |
| 73 | |
| 74 | <h2 id="v3-enhance">Version 3 enhancements</h2> |
| 75 | |
| 76 | <p>The aim of the Android Camera API redesign is to substantially increase the |
| 77 | ability of applications to control the camera subsystem on Android devices while |
| 78 | reorganizing the API to make it more efficient and maintainable.</p> |
| 79 | |
| 80 | <p>The additional control makes it easier to build high-quality camera applications |
| 81 | on Android devices that can operate reliably across multiple products while |
| 82 | still using device-specific algorithms whenever possible to maximize quality and |
| 83 | performance.</p> |
| 84 | |
| 85 | <p>Version 3 of the camera subsystem structures the operation modes into a single |
| 86 | unified view, which can be used to implement any of the previous modes and |
| 87 | several others, such as burst mode. This results in better user control for |
| 88 | focus and exposure and more post-processing, such as noise reduction, contrast |
| 89 | and sharpening. Further, this simplified view makes it easier for application |
| 90 | developers to use the camera's various functions.<br/> |
| 91 | The API models the camera subsystem as a pipeline that converts incoming |
| 92 | requests for frame captures into frames, on a 1:1 basis. The requests |
| 93 | encapsulate all configuration information about the capture and processing of a |
| 94 | frame. This includes: resolution and pixel format; manual sensor, lens and flash |
| 95 | control; 3A operating modes; RAW->YUV processing control; statistics generation; |
| 96 | and so on.</p> |
| 97 | |
| 98 | <p>In simple terms, the application framework requests a frame from the camera |
| 99 | subsystem, and the camera subsystem returns results to an output stream. In |
| 100 | addition, metadata that contains information such as color spaces and lens |
| 101 | shading is generated for each set of results. The following sections and |
| 102 | diagrams give you more detail about each component.<br/> |
| 103 | You can think of camera version 3 as a pipeline to camera version 1's one-way |
| 104 | stream. It converts each capture request into one image captured by the sensor, |
| 105 | which is processed into: </p> |
| 106 | |
| 107 | <ul> |
| 108 | <li>A Result object with metadata about the capture.</li> |
| 109 | <li>One to N buffers of image data, each into its own destination Surface.</li> |
| 110 | </ul> |
| 111 | |
| 112 | <p>The set of possible output Surfaces is preconfigured:</p> |
| 113 | |
| 114 | <ul> |
| 115 | <li>Each Surface is a destination for a stream of image buffers of a fixed |
| 116 | resolution.</li> |
| 117 | <li>Only a small number of Surfaces can be configured as outputs at once (~3).</li> |
| 118 | </ul> |
| 119 | |
| 120 | <p>A request contains all desired capture settings and the list of output Surfaces |
| 121 | to push image buffers into for this request (out of the total configured set). A |
| 122 | request can be one-shot ( with capture() ), or it may be repeated indefinitely |
| 123 | (with setRepeatingRequest() ). Captures have priority over repeating |
| 124 | requests.</p> |
| 125 | <img src="images/camera_simple_model.png" alt="Camera data model"/> |
| 126 | <p><strong>Figure 2.</strong> Camera core operation model</p> |
| 127 | |
| 128 | <h2 id="supported-version">Supported version</h2> |
| 129 | |
| 130 | <p>Camera devices that support this version of the HAL must return |
| 131 | CAMERA_DEVICE_API_VERSION_3_1 in camera_device_t.common.version and in |
| 132 | camera_info_t.device_version (from camera_module_t.get_camera_info).<br/> |
| 133 | Camera modules that may contain version 3.1 devices must implement at least |
| 134 | version 2.0 of the camera module interface (as defined by |
| 135 | camera_module_t.common.module_api_version).<br/> |
| 136 | See camera_common.h for more versioning details.</p> |
| 137 | |
| 138 | <h2 id="version-history">Version history</h2> |
| 139 | |
| 140 | <h4><strong>1.0</strong></h4> |
| 141 | |
| 142 | <p>Initial Android camera HAL (Android 4.0) [camera.h]:</p> |
| 143 | |
| 144 | <ul> |
| 145 | <li>Converted from C++ CameraHardwareInterface abstraction layer.</li> |
| 146 | <li>Supports android.hardware.Camera API.</li> |
| 147 | </ul> |
| 148 | |
| 149 | <h4><strong>2.0</strong></h4> |
| 150 | |
| 151 | <p>Initial release of expanded-capability HAL (Android 4.2) [camera2.h]:</p> |
| 152 | |
| 153 | <ul> |
| 154 | <li>Sufficient for implementing existing android.hardware.Camera API.</li> |
| 155 | <li>Allows for ZSL queue in camera service layer</li> |
| 156 | <li>Not tested for any new features such manual capture control, Bayer RAW |
| 157 | capture, reprocessing of RAW data.</li> |
| 158 | </ul> |
| 159 | |
| 160 | <h4><strong>3.0</strong></h4> |
| 161 | |
| 162 | <p>First revision of expanded-capability HAL:</p> |
| 163 | |
| 164 | <ul> |
| 165 | <li>Major version change since the ABI is completely different. No change to the |
| 166 | required hardware capabilities or operational model from 2.0.</li> |
| 167 | <li>Reworked input request and stream queue interfaces: Framework calls into HAL |
| 168 | with next request and stream buffers already dequeued. Sync framework support |
| 169 | is included, necessary for efficient implementations.</li> |
| 170 | <li>Moved triggers into requests, most notifications into results.</li> |
| 171 | <li>Consolidated all callbacks into framework into one structure, and all setup |
| 172 | methods into a single initialize() call.</li> |
| 173 | <li>Made stream configuration into a single call to simplify stream management. |
| 174 | Bidirectional streams replace STREAM_FROM_STREAM construct.</li> |
| 175 | <li>Limited mode semantics for older/limited hardware devices.</li> |
| 176 | </ul> |
| 177 | |
| 178 | <h4><strong>3.1</strong></h4> |
| 179 | |
| 180 | <p>Minor revision of expanded-capability HAL:</p> |
| 181 | |
| 182 | <ul> |
| 183 | <li>configure_streams passes consumer usage flags to the HAL.</li> |
| 184 | <li>flush call to drop all in-flight requests/buffers as fast as possible.</li> |
| 185 | </ul> |