Android Camera2 API Image Color space

问题

I used this Tutorial to learn and try understand how to make a simple picture taking android app using the Camera2 API. I have added some snippets from the code to see if you all can help me understand some questions I have.

I am trying to find out how the image is saved as. Is it RGB, or BGR? Is it stored in the variable bytes?

ImageReader reader = ImageReader.newInstance(width,height,ImageFormat.JPEG, 1);


@Override
public void onImageAvailable(ImageReader reader) {
      Image image = null;
      try {
            image = reader.acquireLatestImage();
            ByteBuffer buffer = image.getPlanes()[0].getBuffer();
            byte[] bytes = new byte[buffer.capacity()];
            buffer.get(bytes);
            save(bytes);
      }

回答1:

The image is received in JPEG format (as specified in the first line). Android uses YUV (to be more exact, YCbCr) color space for JPEG. Jpeg size is variable, it is compressed with lossy compression, and you have very little control over the level of compression.

Normally, you receive a JPEG buffer in onImageAvailable() and decode this JPEG to receive a Bitmap. You can get pixels of this Bitmap as an int array of packed SRGB pixels. The format for this array will be ARGB_8888. You don't need JNI to convert it to BGR, see this answer.

You can access Bitmap objects from C++, see ndk/reference/group/bitmap. There you can find the pixel format of this bitmap. If it was decoded from JPEG, you should expect this to be ANDROID_BITMAP_FORMAT_RGBA_8888.

回答2:

The variable bytes contains an entire compressed JPEG file. You need to decompress it to do anything much with it, such as with BitmapFactory.decodeByteArray or ImageDecoder (newer API levels).

It's not an uncompressed array of RGB values in any sense. If you want uncompressed data, the camera API supports the YUV_420_888 format, which will give you uncompressed 4:2:0 YUV data; still not RGB, though.

来源：https://stackoverflow.com/questions/65283769/android-camera2-api-image-color-space

标签

java

android

android-camera2