Get RGB from a SurfaceView displaying Live camera

Question

I am displaying a live camera in SurfaceView using camera.startPreview();. Any idea on how I can get live RGB readings from the camera?

Thanks

Answer 1

I thought I could get the data converted from the SurfaceView. But the best method to use is :

• Set the camera's orientation to 90 degrees.
• Set output format to NV21 (which is guranteed to be supported on all devices).
• Set to turn the Flash ON.
• Start preview in the SurfaceView.

List item

camera = Camera.open();
cameraParam = camera.getParameters();
cameraParam.setPreviewFormat(ImageFormat.NV21);
camera.setDisplayOrientation(90);
camera.setParameters(cameraParam);
cameraParam = camera.getParameters();
camera.setPreviewDisplay(surfaceHolder);
cameraParam.setFlashMode(Parameters.FLASH_MODE_TORCH);
camera.setParameters(cameraParam);
camera.startPreview();

Then, I call the setPreviewCallback and onPreviewFrame to get the incoming frame, and convert it to RGB pixel array. Which I can then get intensity of each color in the picture by averaging all pixels intensity by running myPixels array through a for loop, and checking Color.red(myPixels[i]) for each desired color (inside the onPreviewFrame).

camera.setPreviewCallback(new PreviewCallback() {
    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        int frameHeight = camera.getParameters().getPreviewSize().height;
        int frameWidth = camera.getParameters().getPreviewSize().width;
        // number of pixels//transforms NV21 pixel data into RGB pixels  
        int rgb[] = new int[frameWidth * frameHeight];
        // convertion
        int[] myPixels = decodeYUV420SP(rgb, data, frameWidth, frameHeight);
    }
}

Where decodeYUV420SP is found here.

I timed this operation to take about 200ms for each frame. Is there a faster way of doing it?

Answer 2

You can do similar something like below

camera.takePicture(shutterCallback, rawCallback, jpegCallback);

    jpegCallback = new PictureCallback() {
    public void onPictureTaken(byte[] data, Camera camera) {
        FileOutputStream outStream = null;
        try {
            Bitmap bitmap = BitmapFactory.decodeByteArray(data, offset, length);

         int[] pix = new int[picw * pich];
         bitmap.getPixels(pix, 0, picw, 0, 0, picw, pich);

         int R, G, B,Y;

         for (int y = 0; y < pich; y++){
         for (int x = 0; x < picw; x++)
             {
             int index = y * picw + x;
             int R = (pix[index] >> 16) & 0xff;     //bitwise shifting
             int G = (pix[index] >> 8) & 0xff;
             int B = pix[index] & 0xff;

             pix[index] = 0xff000000 | (R << 16) | (G << 8) | B;
             }}


        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
        }
     }
};

here camera.takePicture(shutterCallback, rawCallback, jpegCallback); method call on image capture time , so i think you need to do continually call this method while you camera is open .

Answer 3

as requested here is a fast decoding using NDK ( less then 10 ms on fast device ):

first here is the native.h

#include <jni.h>
#ifndef native_H
#define native_H
extern "C" {
JNIEXPORT jbyteArray JNICALL Com_example_MainActivity_nativeSetIamgeFromCamera(JNIEnv* jenv, jobject obj,jbyteArray array,jint length,jint x,jint y);
};
#endif

native.cpp

    #include <stdint.h>
        #include <jni.h>
        #include <stdlib.h>
        #include <string.h>
        #include <stdio.h>
        #include <android/native_window.h>
        #include <android/native_window_jni.h>
        #include <sys/types.h>
        #include <stdio.h>
        #include <string.h>
        #include <sys/types.h>
        #include <time.h>
        #include "native.h"

void Resize_and_decodyuv(unsigned char * data,int _width,int _height, unsigned char *out, int newWidth, int newHeight);

JNIEXPORT jbyteArray JNICALL Com_example_MainActivity_nativeSetIamgeFromCamera(JNIEnv* jenv, jobject obj,jbyteArray array,jint length,jint x,jint y)
    {
    //-----jbyteArray array contain the data from the camera passed by the java function
    //-----length represent the size of jbyteArray in byte
    //-----x,y respectively resolutionx and resolutiony of the image in jbyteArray array

    unsigned char * buffImgCamera=(unsigned char *)malloc(length);

    //----- copy the buffer from java array to c/c++ char * buffImgCamera
    jenv->GetByteArrayRegion(array, 0, length, (jbyte*)buffImgCamera);

   int width=400,height=600;//screen reso of the surface(400,800 is just an example)
   unsigned char * buffOut=(unsigned char *)malloc(width*height*4);//prepare the result buffer where 4 represent R G B A(Alpha transparency channel).


    //--- to gain time i decode and resize the image to fit the surface screen in one loop
    Resize_and_decodyuv(buffImgCamera,x,y,buffOut,width,height);
    //---copy the result to a jbytearray and return it to java function
    jbyteArray result=env->NewByteArray(width*height*4);
    env->SetByteArrayRegion( result, 0, width*height*4, buffOut);

    return result;
    }



void Resize_and_decodyuv(unsigned char * data,int _width,int _height, unsigned char *out, int newWidth, int newHeight)
    {


int Colordeep=4;//RGBA; in the case of Qt Frame Work or Borland just put 3and the code should work;

        float scaleWidth =  (float)newWidth / (float)_width;
        float scaleHeight = (float)newHeight / (float)_height;


        for(int cy = 0; cy < newHeight; cy++)
        {
            for(int cx = 0; cx < newWidth; cx++)
            {
                int pixel = (cy * (newWidth *Colordeep)) + (cx*Colordeep);
                int nearestMatch =  ((((int)(cy / scaleHeight)) *_width) + (int)(cx /scaleWidth));

                int cxa=cx/scaleWidth;
                int cya=cy/scaleHeight; cya/=2;
                int nearestMatch1 =(cya *_width) + (int)(cxa);




                int y =  ( data[nearestMatch]);

                      int v = data[data_uv+(nearestMatch1)];
                      int u = data[data_uv+(nearestMatch1)+1];



                      int r = (int) (1164 * (y - 16) + 1596 * (v - 128));
                      int g = (int) (1164 * (y - 16) - 813 * (v - 128) - 391 * (u - 128));
                      int b = (int) (1164 * (y - 16) + 2018 * (u - 128));
          r/=1000;
          g/=1000;
          b/=1000;
                      r = r < 0 ? 0 : (r > 255 ? 255 : r);
                      g = g < 0 ? 0 : (g > 255 ? 255 : g);
                      b = b < 0 ? 0 : (b > 255 ? 255 : b);



                out[pixel ] = r;
                out[pixel  +1  ] =  g;
                out[pixel + 2] =  b;
                if(Colordeep==4)out[pixel + 3] =  255;


            }
        }


    }

java code

PreviewCallback previewCallback = new PreviewCallback () {


            public void onPreviewFrame(byte[] data, Camera camera) {
                //nativeSetIamgeFromCamera return a byte array  
                nativeSetIamgeFromCamera(data,data.length,camera.getParameters().getPreviewSize().width,camera.getParameters().getPreviewSize().height);


            }
    };