将YUV_420_888转换为JPEG并保存文件会导致图像失真

Question

我在我的git repo中使用了/sf/answers/2810650321/中ImageUtil提供的类:https://github.com/ahasbini/cameraview/tree/camera_preview_imp(注意实现在分支中)到实现帧预览回调.一个被设置为预览在帧格式将被转换成使用类,并将其发送给帧的回调.演示应用程序每50帧将回调帧保存到文件中.所有保存的帧图像都会失真,类似于以下内容:camera_preview_impImageReaderImageFormat.YUV_420_888ImageFormat.JPEGImageUtil

如果我通过执行以下更改而改为ImageReader使用:ImageFormat.JPEGCamera2

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

图像正常运行而没有任何失真,但帧速率显着下降,视图开始滞后.因此,我认为ImageUtil班级没有正确转换.

Answer 1

@ volodymyr-kulyk提供的解决方案没有考虑图像中平面的行间距.下面的代码不会把戏(image是的android.media.Image类型):

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

实施:

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;
}

方法来自以下链接.