1 <html devsite> 2 <head> 3 <title>Output streams and cropping</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="output-stream">Output streams</h2> 27 <p> Unlike the old camera subsystem, which has 3-4 different ways of producing data 28 from the camera (ANativeWindow-based preview operations, preview callbacks, 29 video callbacks, and takePicture callbacks), the new subsystem operates solely 30 on the ANativeWindow-based pipeline for all resolutions and output formats. 31 Multiple such streams can be configured at once, to send a single frame to many 32 targets such as the GPU, the video encoder, RenderScript, or app-visible buffers 33 (RAW Bayer, processed YUV buffers, or JPEG-encoded buffers).</p> 34 <p>As an optimization, these output streams must be configured ahead of time, and 35 only a limited number may exist at once. This allows for pre-allocation of 36 memory buffers and configuration of the camera hardware, so that when requests 37 are submitted with multiple or varying output pipelines listed, there won't be 38 delays or latency in fulfilling the request.</p> 39 <p>To support backwards compatibility with the current camera API, at least 3 40 simultaneous YUV output streams must be supported, plus one JPEG stream. This is 41 required for video snapshot support with the application also receiving YUV 42 buffers:</p> 43 <ul> 44 <li>One stream to the GPU/SurfaceView (opaque YUV format) for preview</li> 45 <li>One stream to the video encoder (opaque YUV format) for recording</li> 46 <li>One stream to the application (known YUV format) for preview frame callbacks</li> 47 <li>One stream to the application (JPEG) for video snapshots.</li> 48 </ul> 49 <p>The exact requirements are still being defined since the corresponding API 50 isn't yet finalized.</p> 51 <h2>Cropping</h2> 52 <p>Cropping of the full pixel array (for digital zoom and other use cases where a 53 smaller FOV is desirable) is communicated through the ANDROID_SCALER_CROP_REGION 54 setting. This is a per-request setting, and can change on a per-request basis, 55 which is critical for implementing smooth digital zoom.</p> 56 <p>The region is defined as a rectangle (x, y, width, height), with (x, y) 57 describing the top-left corner of the rectangle. The rectangle is defined on the 58 coordinate system of the sensor active pixel array, with (0,0) being the 59 top-left pixel of the active pixel array. Therefore, the width and height cannot 60 be larger than the dimensions reported in the ANDROID_SENSOR_ACTIVE_PIXEL_ARRAY 61 static info field. The minimum allowed width and height are reported by the HAL 62 through the ANDROID_SCALER_MAX_DIGITAL_ZOOM static info field, which describes 63 the maximum supported zoom factor. Therefore, the minimum crop region width and 64 height are:</p> 65 <pre class="devsite-click-to-copy"> 66 {width, height} = 67 { floor(ANDROID_SENSOR_ACTIVE_PIXEL_ARRAY[0] / 68 ANDROID_SCALER_MAX_DIGITAL_ZOOM), 69 floor(ANDROID_SENSOR_ACTIVE_PIXEL_ARRAY[1] / 70 ANDROID_SCALER_MAX_DIGITAL_ZOOM) } 71 </pre> 72 <p>If the crop region needs to fulfill specific requirements (for example, it needs 73 to start on even coordinates, and its width/height needs to be even), the HAL 74 must do the necessary rounding and write out the final crop region used in the 75 output result metadata. Similarly, if the HAL implements video stabilization, it 76 must adjust the result crop region to describe the region actually included in 77 the output after video stabilization is applied. In general, a camera-using 78 application must be able to determine the field of view it is receiving based on 79 the crop region, the dimensions of the image sensor, and the lens focal length.</p> 80 <p>Since the crop region applies to all streams, which may have different aspect 81 ratios than the crop region, the exact sensor region used for each stream may be 82 smaller than the crop region. Specifically, each stream should maintain square 83 pixels and its aspect ratio by minimally further cropping the defined crop 84 region. If the stream's aspect ratio is wider than the crop region, the stream 85 should be further cropped vertically, and if the stream's aspect ratio is 86 narrower than the crop region, the stream should be further cropped 87 horizontally.</p> 88 <p>In all cases, the stream crop must be centered within the full crop region, and 89 each stream is only either cropped horizontally or vertical relative to the full 90 crop region, never both.</p> 91 <p>For example, if two streams are defined, a 640x480 stream (4:3 aspect), and a 92 1280x720 stream (16:9 aspect), below demonstrates the expected output regions 93 for each stream for a few sample crop regions, on a hypothetical 3 MP (2000 x 94 1500 pixel array) sensor.</p> 95 </p> 96 Crop region: (500, 375, 1000, 750) (4:3 aspect ratio)<br/> 97 640x480 stream crop: (500, 375, 1000, 750) (equal to crop region)<br/> 98 1280x720 stream crop: (500, 469, 1000, 562) 99 </p> 100 <img src="images/crop-region-43-ratio.png" alt="crop-region-43-ratio" id="figure1" /> 101 <p class="img-caption"> 102 <strong>Figure 1.</strong> 4:3 aspect ratio 103 </p> 104 <p>Crop region: (500, 375, 1333, 750) (16:9 aspect ratio)<br/> 105 640x480 stream crop: (666, 375, 1000, 750)<br/> 106 1280x720 stream crop: (500, 375, 1333, 750) (equal to crop region) 107 </p> 108 <img src="images/crop-region-169-ratio.png" alt="crop-region-169-ratio" id="figure2" /> 109 <p class="img-caption"> 110 <strong>Figure 2.</strong> 16:9 aspect ratio 111 </p> 112 <p>Crop region: (500, 375, 750, 750) (1:1 aspect ratio)<br/> 113 640x480 stream crop: (500, 469, 750, 562)<br/> 114 1280x720 stream crop: (500, 543, 750, 414) 115 </p> 116 <img src="images/crop-region-11-ratio.png" alt="crop-region-11-ratio" id="figure3" /> 117 <p class="img-caption"> 118 <strong>Figure 3.</strong> 1:1 aspect ratio 119 </p> 120 <p> 121 And a final example, a 1024x1024 square aspect ratio stream instead of the 480p 122 stream:<br/> 123 Crop region: (500, 375, 1000, 750) (4:3 aspect ratio)<br/> 124 1024x1024 stream crop: (625, 375, 750, 750)<br/> 125 1280x720 stream crop: (500, 469, 1000, 562) 126 </p> 127 <img src="images/crop-region-43-square-ratio.png" alt="crop-region-43-square-ratio" id="figure4" /> 128 <p class="img-caption"> 129 <strong>Figure 4.</strong> 4:3 aspect ratio, square 130 </p> 131 <h2 id="reprocessing">Reprocessing</h2> 132 <p> Additional support for raw image files is provided by reprocessing support for RAW Bayer 133 data. This support allows the camera pipeline to process a previously captured 134 RAW buffer and metadata (an entire frame that was recorded previously), to 135 produce a new rendered YUV or JPEG output.</p> 136 137 </body> 138 </html> 139
