CODEWITHSUNDEEP
androidresolutionandroid-camera2
Jun Fang
Jun Fang

Reputation: 351

What's relationship between preview image size and captured image size in Android camera2 API?

I am using camera2 API to building an image processing project in Android. I use TextureView to get a preview screen, and ImageReader to obtain image frames. For the purpose of image processing, I need to obtain frames with maximal size in ImageReader, and don't has any requirements on the size of preview frames. So I set the size of frames respectively with following codes:

        StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        imageDimension = map.getOutputSizes(SurfaceTexture.class)[0];
        texture.setDefaultBufferSize(imageDimension.getWidth(), imageDimension.getHeight());

        List<Size> outputSizes = Arrays.asList(map.getOutputSizes(sImageFormat));
        largest = Collections.max(outputSizes, new CompareSizesByArea());
        mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(), sImageFormat, 1);

In may testing Android device Huawei P9: imageDimension is:1280*720; largest is: 3968*2976.

I found that the preview screen works well, however, the captured image in the onImageAvailable is completely black, I guess that nothing is captured.

I tried two ways to figure out what's going on here. 1) I set the size of ImageReader to imageDimension and found that the captured image is OK. 2) I set the size of preview frames to largest and found the preview screen is black.

Hence, I wonder if the size of captured image in ImageReader should less than that of preview frames. It it is the case, how can I set the maximal resolution of preview frame?

Anyway, my purpose is to obtain frames with maximal resolution as well as fluent preview screen. Any suggestions are welcome. Thanks.

Upvotes: 0

Views: 1683

Answers (2)

Alex Cohn
Alex Cohn

Reputation: 57173

On some devices, capture may take much longer if the aspect ratio of the capture does not fit the aspect ratio of preview.

Upvotes: 0

Eddy Talvala
Eddy Talvala

Reputation: 18107

In theory, the resolution of two separate outputs should make no difference, as long as you're within the resolution guarantees for multiple streams listed in the tables at the documentation for CameraDevice.createCaptureSession(). If you're operating at resolution above those guarantees, things may not work as expected.

In general, I'd recommend keeping the preview resolution <= 1080p (1920x1080); many devices cannot produce smooth 30fps preview at resolutions above that size; some may even require 720p or lower. Also, the GPU on a device may not actually be able to handle full-resolution camera output, which may explain some of the black preview output.

There's no reason that the ImageReader needs to be smaller than the preview; I suspect you may just have too high of a preview size.

So try a configuration of:

  • Full-resolution ImageReader
  • 1080p or similar preview

Upvotes: 1

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