android - 将 YUV_420_888 转换为 JPEG 并保存文件导致图像失真

Question

我用过 ImageUtil https://stackoverflow.com/a/40152147/2949966 中提供的类在我的 git 仓库中:https://github.com/ahasbini/cameraview/tree/camera_preview_imp (注意实现在 camera_preview_imp 分支中)实现帧预览回调。一个ImageReader设置为在 ImageFormat.YUV_420_888 中预览帧将转换为 ImageFormat.JPEG 的格式使用 ImageUtil类并将其发送到帧回调。演示应用程序每 50 帧将回调中的一帧保存到一个文件中。所有保存的帧图像都出现扭曲，类似于以下内容:

如果我改变了 ImageReader使用 ImageFormat.JPEG而不是在 Camera2 中进行以下更改:

mPreviewImageReader = ImageReader.newInstance(previewSize.getWidth(),
    previewSize.getHeight(), ImageFormat.JPEG, /* maxImages */ 2);
mCamera.createCaptureSession(Arrays.asList(surface, mPreviewImageReader.getSurface()),
    mSessionCallback, null);

图像正常显示，没有任何失真，但帧速率显着下降并且 View 开始滞后。因此我相信 ImageUtil类未正确转换。

Answer 1

@volodymyr-kulyk 提供的解决方案没有考虑图像中平面的行步幅。下面的代码可以解决问题(image 是 android.media.Image 类型):

data = NV21toJPEG(YUV420toNV21(image), image.getWidth(), image.getHeight(), 100);

和实现:

private static byte[] NV21toJPEG(byte[] nv21, int width, int height, int quality) {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    YuvImage yuv = new YuvImage(nv21, ImageFormat.NV21, width, height, null);
    yuv.compressToJpeg(new Rect(0, 0, width, height), quality, out);
    return out.toByteArray();
}

private static byte[] YUV420toNV21(Image image) {
    Rect crop = image.getCropRect();
    int format = image.getFormat();
    int width = crop.width();
    int height = crop.height();
    Image.Plane[] planes = image.getPlanes();
    byte[] data = new byte[width * height * ImageFormat.getBitsPerPixel(format) / 8];
    byte[] rowData = new byte[planes[0].getRowStride()];

    int channelOffset = 0;
    int outputStride = 1;
    for (int i = 0; i < planes.length; i++) {
        switch (i) {
            case 0:
                channelOffset = 0;
                outputStride = 1;
                break;
            case 1:
                channelOffset = width * height + 1;
                outputStride = 2;
                break;
            case 2:
                channelOffset = width * height;
                outputStride = 2;
                break;
        }

        ByteBuffer buffer = planes[i].getBuffer();
        int rowStride = planes[i].getRowStride();
        int pixelStride = planes[i].getPixelStride();

        int shift = (i == 0) ? 0 : 1;
        int w = width >> shift;
        int h = height >> shift;
        buffer.position(rowStride * (crop.top >> shift) + pixelStride * (crop.left >> shift));
        for (int row = 0; row < h; row++) {
            int length;
            if (pixelStride == 1 && outputStride == 1) {
                length = w;
                buffer.get(data, channelOffset, length);
                channelOffset += length;
            } else {
                length = (w - 1) * pixelStride + 1;
                buffer.get(rowData, 0, length);
                for (int col = 0; col < w; col++) {
                    data[channelOffset] = rowData[col * pixelStride];
                    channelOffset += outputStride;
                }
            }
            if (row < h - 1) {
                buffer.position(buffer.position() + rowStride - length);
            }
        }
    }
    return data;
}

方法来自以下link .