使用 Android 的相机 2 拍摄灰度照片

Question

I am creating an app for taking pictures and sending them via http POST to my server. Since I only need grayscale data on the server side, it would by much better to just take the grayscale picture and not having to convert it. I am using Camera2 API and I have an issue with setting properties for CaptureRequest.Builder instance. With this:

final CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.set(CaptureRequest.CONTROL_EFFECT_MODE, CaptureRequest.CONTROL_EFFECT_MODE_NEGATIVE);

It takes a negative photo. But this:

final CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.set(CaptureRequest.CONTROL_EFFECT_MODE, CaptureRequest.CONTROL_EFFECT_MODE_MONO);

Does absolutely nothing. No grayscale. just a normal picture.

Answer 1

You need to look at the list of supported effects on your device, to see if MONO is actually supported by it.

If you only care about luminance, you could just capture YUV_420_888 buffers instead of JPEG, and only send the Y buffer to the server. That won't get you automatic JPEG encoding, though.

Also note that generally under the hood, JPEG images are encoded in YUV; so if you dig into your JPEG decoder library, you may be able to get the image data before conversion to RGB, and simply ignore the chroma channels.

Answer 2

captureRequestBuilder.set(CaptureRequest.CONTROL_EFFECT_MODE,CameraMetadata.CONTROL_EFFECT_MODE_MONO);

你可以用这个`