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Android Camera2 YUV to RGB conversion turns out green?

asked 2015-05-11 04:37:39 -0500

franz gravatar image

updated 2015-05-11 08:49:22 -0500

So I'm getting Image objects from Android's Camera2 API, then I convert them to OpenCV Mat objects via their byte buffers. The YUV_420_888 format is what I set as the output of the camera as recommended by the docs, but when I try converting the Mat from YUV to RGB, all it shows is green.

Following the answers from this thread, this is how I convert the Mat:

Image image = reader.acquireLatestImage();

ByteBuffer buffer = image.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.remaining()];

Mat mat = new Mat(image.getHeight()+image.getHeight()/2, image.getWidth(), CvType.CV_8UC1);
mat.put(0, 0, bytes);
Mat rgb = new Mat(image.getHeight(), image.getWidth(), CvType.CV_8UC4);
Imgproc.cvtColor(mat, rgb, Imgproc.COLOR_YUV420sp2BGR, 4);

After these lines, all I did next was use imwrite to write the mats to disk. For reference, here's some sample images resulting from the writes:

YUV - (straight from the Camera2 API, no processing yet)

RGB - (the exact same image, but converted from YUV to RGB)

Any insights as to why the RGB image looks the way it does? I've also tried a whole lot of other conversion options besides COLOR_YUV420sp2BGR, but they all seem to have the same effect, which is a green image. Thank you in advance!

EDIT: As has been pointed out in the comments, it seems I need to use all 3 planes of the YUV image, and not just the first one. I know how to convert each plane into a byte array, and now I have 3 byte arrays each representing a plane, but my question is now how do I create a Mat from these 3 byte arrays? The put() method I'm familiar with only accepts a single byte array. Do I concatenate or combine them somehow?

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I guess (but just a guess) the problem is here ByteBuffer buffer = image.getPlanes()[0].getBuffer(); You're just using the 0-plane of the image, but you have 3 planes: Y, U and V.

LorenaGdL gravatar imageLorenaGdL ( 2015-05-11 04:51:47 -0500 )edit

Thanks for the reply! That part of the code I actually based it from the official Camera2 example found here. It does initiate it with the 0-plane, but I just assume buffer.getBytes() does the rest of the job as when I run this example, the results are fully colored. Though the difference is the format was set to JPEG, not YUV. So are you saying that since I changed the format from JPEG to YUV, I must retrieve not just the 0-plane?

franz gravatar imagefranz ( 2015-05-11 04:59:57 -0500 )edit

Also, if I do indeed get byte arrays for the 3 planes, how would I create a Mat from that? From the examples I saw, using the Mat's put() method accepts a single byte array. Now that I have 3 byte arrays, how do I combine them into a single one in order to pass them to put() ? Or should I create Mats using a different method or constructor? I browsed the docs for the Mat object, but I don't see any method or constructor which accepts 3 byte arrays simultaneously?

franz gravatar imagefranz ( 2015-05-11 05:06:53 -0500 )edit

I'm not familiarized with the API, so I can't really help, but it seems unnatural to me to use just one single plane when you're working with the YUV color space. Anyway I may be fully wrong.

LorenaGdL gravatar imageLorenaGdL ( 2015-05-11 06:29:32 -0500 )edit

Another thing, why do you have a 4 here?Imgproc.cvtColor(mat, rgb, Imgproc.COLOR_YUV420sp2BGR, 4); Doesn't the 4 indicate the number of channels in the ouput image? If so, you only have 3 (you can even omit the number I think)

LorenaGdL gravatar imageLorenaGdL ( 2015-05-11 06:33:37 -0500 )edit

Alright, thank you for your insights, they're very helpful! Anyway, yes I think you're right, that should be 3 and not 4.

franz gravatar imagefranz ( 2015-05-11 08:31:32 -0500 )edit

OK, after a new look at your code I've spotted another important thing: in the definition of mat, there's this CvType.CV_8UC1 when you should have CvType.CV_8UC3 as you're storing 3 channels (same on the output mat)

LorenaGdL gravatar imageLorenaGdL ( 2015-05-12 02:52:30 -0500 )edit

6 answers

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answered 2016-01-18 23:17:15 -0500

I have been able to do it successfully.

    Image.Plane Y = image.getPlanes()[0];
    Image.Plane U = image.getPlanes()[1];
    Image.Plane V = image.getPlanes()[2];

    int Yb = Y.getBuffer().remaining();
    int Ub = U.getBuffer().remaining();
    int Vb = V.getBuffer().remaining();

    byte[] data = new byte[Yb + Ub + Vb];

    Y.getBuffer().get(data, 0, Yb);
    U.getBuffer().get(data, Yb, Ub);
    V.getBuffer().get(data, Yb+ Ub, Vb);

I'm using OpenCV JNI and was able to convert it to BGR image using CV_YUV2BGR_I420 with cvtColor

Here's my C++ code.

jboolean Java_com_fenchtose_myPackage_myClass_myMethod(
        JNIEnv* env, jobject thiz,
        jint width, jint height,
        jbyteArray YUVFrameData)
    jbyte * pYUVFrameData = env->GetByteArrayElements(YUVFrameData, 0);

    double alpha;
    alpha = (double) alphaVal;

    Mat mNV(height + height/2, width, CV_8UC1, (unsigned char*)pYUVFrameData);
    Mat mBgr(height, width, CV_8UC3);

    cv::cvtColor(mNV, mBgr, CV_YUV2BGR_I420);

    env->ReleaseByteArrayElements(YUVFrameData, pYUVFrameData, 0);

    return true;
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this will not work if the pixel stride is 2, see (awaiting moderation)

zarokka gravatar imagezarokka ( 2016-08-16 03:11:54 -0500 )edit

answered 2018-09-21 22:10:23 -0500

I have a image(YUV_420_888) that captured by ARCore in pixel, and want to covert it to Mat.

I have try the first answer(, but it failed.I can't get the rgb image by save the picture using the opencv function: imwrite().

And then, I try the second answer(, I failed too. because in the image that saved by imwrite(), red object covert to green.

Finally, because of a little accident, I try the code that YUV to data(byte[]) that write in the first answer, and try the code that data(byte[]) to Mat that writes in the second answer, and I successd.

---------- Java

    Image.Plane Y = image.getPlanes()[0];
    Image.Plane U = image.getPlanes()[1];
    Image.Plane V = image.getPlanes()[2];

    int Yb = Y.getBuffer().remaining();
    int Ub = U.getBuffer().remaining();
    int Vb = V.getBuffer().remaining();

    byte[] data = new byte[Yb + Ub + Vb];

    Y.getBuffer().get(data, 0, Yb);
    U.getBuffer().get(data, Yb, Ub);
    V.getBuffer().get(data, Yb+ Ub, Vb);

    return data;

--------- OpenCV JNI ,c++

extern "C"
    (JNIEnv *env, jobject jobj, jbyteArray _pixels1, jbyteArray _pixels2, jint width, jint height)

jbyte *pixels1 = env->GetByteArrayElements(_pixels1 , NULL);
jbyte *pixels2 = env->GetByteArrayElements(_pixels2 , NULL);

    int size = -1;
    jintArray result = env->NewIntArray(size);
    return result;
Mat lyuvMat(height + (height / 2), width, CV_8UC1, (unsigned char*)pixels1);
imwrite("/storage/emulated/0/camoutput/xly/lyuv.jpg", lyuvMat);
Mat lrgbMat(height, width, CV_8UC3);
cvtColor(lyuvMat, lrgbMat, COLOR_YUV2RGB_NV21, 3);
imwrite("/storage/emulated/0/camoutput/xly/lrgb.jpg", lrgbMat);


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answered 2018-08-30 04:43:13 -0500

COLOR_YUV420sp2BGRA 或许你应该使用这个答案,我在face 上也有部分有色变绿,希望对你有用。

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answered 2018-09-24 05:20:58 -0500

shyam kumar gravatar image

Camera2 YUV_420_888 to RGB Mat(opencv) in Java

public void onImageAvailable(ImageReader reader){
    Image image = null;

    try {
        image = reader.acquireLatestImage();
        if (image != null) {

            byte[] nv21;
            ByteBuffer yBuffer = mImage.getPlanes()[0].getBuffer();
            ByteBuffer uBuffer = mImage.getPlanes()[1].getBuffer();
            ByteBuffer vBuffer = mImage.getPlanes()[2].getBuffer();

            int ySize = yBuffer.remaining();
            int uSize = uBuffer.remaining();
            int vSize = vBuffer.remaining();

            nv21 = new byte[ySize + uSize + vSize];

            //U and V are swapped
            yBuffer.get(nv21, 0, ySize);
            vBuffer.get(nv21, ySize, vSize);
            uBuffer.get(nv21, ySize + vSize, uSize);

            Mat mRGB = getYUV2Mat(nv21);

    } catch (Exception e) {
        Log.w(TAG, e.getMessage());
        image.close();// don't forget to close

public Mat getYUV2Mat(byte[] data) {
Mat mYuv = new Mat(image.getHeight() + image.getHeight() / 2, size.getWidth(), CV_8UC1);
mYuv.put(0, 0, data);
Mat mRGB = new Mat();
cvtColor(mYuv, mRGB, Imgproc.COLOR_YUV2RGB_NV21, 3);
return mRGB;}
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Mat mYuv = new Mat(image.getHeight() + image.getHeight() / 2, size.getWidth(), CV_8UC1);

Why use the Height twice and divide by 2 ?

LiorA gravatar imageLiorA ( 2020-04-24 13:02:44 -0500 )edit

answered 2020-09-17 04:40:00 -0500

bond gravatar image
  • Read Y, U and V binary files into byte buffers
    • Create OpenCV Mat object from the created buffers.
    • Resize U and V Mats to the size of Y.
    • Merge Y and resized U and V.
    • Convert from YUV to BGR

Size actual_size(1280, 720);
Size half_size(1280/2, 720/2); //Size half_size(1280/2, 720/2);
Mat ndk_rgb_img, ndk_rgb_img_out;
int ndk_image_width = 1280; 
int ndk_image_height = 720;
uint8_t *yPixel, *uPixel, *vPixel;
int32_t yLen, uLen, vLen;
int32_t uvPixelStride;
int32_t uvRowStride;

AImage_getPlaneData(image, 0, &yPixel, &yLen); //Y
AImage_getPlaneData(image, 1, &uPixel, &uLen); // U
AImage_getPlaneData(image, 2, &vPixel, &vLen); //V
AImage_getPlanePixelStride(image, 1, &uvPixelStride); // foulée en pixel
AImage_getPlaneRowStride (image, 1, &uvRowStride); // foulée en ligne

// cout << "length Y " <<  yLen << endl;
// cout << "length U " << uLen << endl;
// cout << "length V " <<  vLen << endl;
//cout << "uvPixelStride " <<  uvPixelStride << endl;
//cout << "uvRowStride " <<  uvRowStride << endl;

Mat y(actual_size, CV_8UC1, yPixel);
Mat u(half_size, CV_8UC2, uPixel); 
Mat v(half_size, CV_8UC2, vPixel); 
long addr_diff = -;
if (addr_diff > 0) { 
    assert(addr_diff == 1); 
    cvtColorTwoPlane(y, u, ndk_rgb_img, COLOR_YUV2BGR_NV12); //COLOR_YUV2RGB_NV12
} else { 
    assert(addr_diff == -1); 
    cvtColorTwoPlane(y, v, ndk_rgb_img, COLOR_YUV2BGR_NV21); 

Work for me very well

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answered 2016-08-16 03:05:14 -0500

zarokka gravatar image

The answer did not fully work for me, it seems that the data format can vary between devices.

The mentioned answer probably works if the pixel stride is 1, but all devices I have available produce images with pixel stride 2 (Nexus 5, Sony Xperia Z3). The pixel stride means that the U and V planes are padded. The full buffer has the size of 2 bytes per pixel.

There is no way to directly convert this padded format with OpenCV currently, but it can be converted to YUV NV21 before converting it to a RGB/BGR image. (NV21 because it requires less work to convert to NV21 than to normal YUV420).

I do not know if a different pixel stride than 1 or 2 is possible (i guess not).

public Mat convertYuv420888ToMat(Image image, boolean isGreyOnly) {
    int width = image.getWidth();
    int height = image.getHeight();

    Image.Plane yPlane = image.getPlanes()[0];
    int ySize = yPlane.getBuffer().remaining();

    if (isGreyOnly) {
        byte[] data = new byte[ySize];
        yPlane.getBuffer().get(data, 0, ySize);

        Mat greyMat = new Mat(height, width, CvType.CV_8UC1);
        greyMat.put(0, 0, data);

        return greyMat;

    Image.Plane uPlane = image.getPlanes()[1];
    Image.Plane vPlane = image.getPlanes()[2];

    // be aware that this size does not include the padding at the end, if there is any
    // (e.g. if pixel stride is 2 the size is ySize / 2 - 1)
    int uSize = uPlane.getBuffer().remaining();
    int vSize = vPlane.getBuffer().remaining();

    byte[] data = new byte[ySize + (ySize/2)];

    yPlane.getBuffer().get(data, 0, ySize);

    ByteBuffer ub = uPlane.getBuffer();
    ByteBuffer vb = vPlane.getBuffer();

    int uvPixelStride = uPlane.getPixelStride(); //stride guaranteed to be the same for u and v planes
    if (uvPixelStride == 1) {
        uPlane.getBuffer().get(data, ySize, uSize);
        vPlane.getBuffer().get(data, ySize + uSize, vSize);

        Mat yuvMat = new Mat(height + (height / 2), width, CvType.CV_8UC1);
        yuvMat.put(0, 0, data);
        Mat rgbMat = new Mat(height, width, CvType.CV_8UC3);
        Imgproc.cvtColor(yuvMat, rgbMat, Imgproc.COLOR_YUV2RGB_I420, 3);
        return rgbMat;

    // if pixel stride is 2 there is padding between each pixel
    // converting it to NV21 by filling the gaps of the v plane with the u values
    vb.get(data, ySize, vSize);
    for (int i = 0; i < uSize; i += 2) {
        data[ySize + i + 1] = ub.get(i);

    Mat yuvMat = new Mat(height + (height / 2), width, CvType.CV_8UC1);
    yuvMat.put(0, 0, data);
    Mat rgbMat = new Mat(height, width, CvType.CV_8UC3);
    Imgproc.cvtColor(yuvMat, rgbMat, Imgproc.COLOR_YUV2RGB_NV21, 3);
    return rgbMat;
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I know it's an old thread, but I've came across your code via Google. For me it showed wrong colors in the resulting Mat. I think the reason for that is a little issue in your NV21 conversion.

Due to NV21 specification the Cr (V) sample (the LSB) is placed in each first and the Cb (U) in each second byte. What you're doing is actually a NV12 conversion.

So, either you should change the conversion algorithm to:

ub.get(data, ySize, uSize);
for (int i = 0; i < vSize; i += 2) {
    data[ySize + i + 1] = vb.get(i);

or change the change the resulting format to NV12:

Imgproc.cvtColor(yuvMat, rgbMat, Imgproc.COLOR_YUV2RGB_NV12, 3);
pjaydev gravatar imagepjaydev ( 2020-03-19 07:41:34 -0500 )edit

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Asked: 2015-05-11 04:37:39 -0500

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Last updated: Sep 24 '18