I am trying to use jpeglib-turbo with android ndk to get the pixel rgb values of a jpeg image, and i am new to both C++,C and android NDK, till now i've tried using the solutions provided in Examples or tutorials of using libjpeg-turbo's TurboJPEG but i am unable to fix the issue at hand, Currently using https://github.com/openstf/android-libjpeg-turbo to build libjpeg-turbo.
Current code is
#include <turbojpeg.h>
#include <jni.h>
#include <android/log.h>
#include <syslog.h>
JNIEXPORT jbyteArray
Java_com_serelay_jpegturbo_MainActivity_getImagePixelData( JNIEnv* env,
jobject this,
jbyteArray data)
{
long unsigned int _jpegSize=2464742; //!< _jpegSize from above
unsigned char *_compressedImage; //!< _compressedImage from above
_compressedImage = data;
int width, height, jpegSubSamp;
// int jpegSubSamp = TJSAMP_444;
tjhandle _jpegDecompressor = tjInitDecompress();
tjDecompressHeader2(_jpegDecompressor, _compressedImage, _jpegSize, &width,
&height, &jpegSubSamp);
unsigned long len = width * height * 4;
unsigned long pitch = width * 4;
syslog(LOG_CRIT, "====================");
syslog(LOG_CRIT, "jpegSize %lu", _jpegSize);
syslog(LOG_CRIT, "width %d", width);
syslog(LOG_CRIT, "height %d", height);
syslog(LOG_CRIT, "total length %lu", len);
syslog(LOG_CRIT, "====================");
unsigned char buffer[len]; //!< will contain the decompressed image
tjDecompress2(_jpegDecompressor, _compressedImage, _jpegSize, buffer, width, pitch, height, TJPF_RGBA, 0);
tjDestroy(_jpegDecompressor);
// char array to byte array
jbyteArray jbytes = buffer;
//jbyteArray jbytes = _compressedImage;
return jbytes;
}
To call it from java i am using public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Example of a call to a native method
TextView tv = (TextView) findViewById(R.id.sample_text);
System.loadLibrary("twolib-second");
InputStream inputStream= getResources().openRawResource(R.raw.image1);
byte[] bytes;
try {
bytes = new byte[inputStream.available()];
inputStream.read(bytes);
byte[] array = getImagePixelData(bytes);
tv.setText(String.valueOf(getImagePixelData(bytes).length));
} catch (IOException e) {
e.printStackTrace();
}
// tv.setText(getImagePixelData(5));
}
/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native byte[] getImagePixelData(byte[] x);
}
I've been successfully calling from the code from java with the help of so files generated by ndk, but the issue i am faced was exceptions in the code which said
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0xeaa6cc30
on further inspection i logged values of some variables which felt a bit bad considering the image being passed is of size 3840*2160, upon logging the variables i get
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
====================
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
jpegSize 2464742
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
width 4
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
height -1386946560
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
total length 3578658816
03-07 20:26:05.180 13613-13613/com.serelay.jpegturbo E/com.serelay.jpegturbo:
====================
i can see the width and height values are very wrong but i can't figure out why and how to fix it. It would be great if any help or directions can be provided to fix this issue, am stuck with this since last 2 days :) thanks.
Changes was required in tjDecompressHeader2 and we needed to use tjDecompressHeader3 in the library version, also we need to convert jbyteArray to unsigned char * and then back to jbyteArray in order to return a byte array to java, both of them can be observed in the code below.
#include <turbojpeg.h>
#include <jni.h>
#include <android/log.h>
#include <syslog.h>
JNIEXPORT jbyteArray
Java_com_serelay_jpegturbo_MainActivity_getImagePixelData( JNIEnv* env,
jobject this,
jbyteArray data,
jint dataLength)
{
long unsigned int _jpegSize=dataLength; //!< _jpegSize from above
unsigned char *_compressedImage; //!< _compressedImage from above
jboolean isCopy;
_compressedImage = (unsigned char*)(*env)->GetByteArrayElements(env, data,
&isCopy);
int width, height, jpegSubSamp, jpegColorSpace;
// int jpegSubSamp = TJSAMP_444;
tjhandle _jpegDecompressor = tjInitDecompress();
tjDecompressHeader3(_jpegDecompressor, _compressedImage, _jpegSize, &width,
&height, &jpegSubSamp, &jpegColorSpace);
long len = width * height * 4;
long pitch = width * 4;
syslog(LOG_CRIT, "====================");
syslog(LOG_CRIT, "jpegSize %lu", _jpegSize);
syslog(LOG_CRIT, "width %d", width);
syslog(LOG_CRIT, "height %d", height);
syslog(LOG_CRIT, "subsampl %d", jpegSubSamp);
syslog(LOG_CRIT, "colorSpace %d", jpegColorSpace);
syslog(LOG_CRIT, "len %lu", len);
syslog(LOG_CRIT, "pitch %lu", pitch);
syslog(LOG_CRIT, "====================");
syslog(LOG_CRIT, "===================0");
unsigned char* mumfer = (unsigned char*)malloc(len); //!< will contain the
decompressed image
syslog(LOG_CRIT, "===================1");
tjDecompress2(_jpegDecompressor, _compressedImage, _jpegSize, mumfer, width,
0, height, TJPF_RGBA, TJFLAG_FASTDCT);
syslog(LOG_CRIT, "===================2");
tjDestroy(_jpegDecompressor);
syslog(LOG_CRIT, "===================3");
// char array to byte array
jbyteArray array = (*env)->NewByteArray(env, len);
syslog(LOG_CRIT, "===================4");
//HERE I GET THE ERROR, I HAVE BEEN TRYING WITH len/2 and WORKS , PROBABLY
SOME BYTS ARE GETTING LOST.
(*env)->SetByteArrayRegion (env, array, 0, len, (jbyte*)(mumfer));
syslog(LOG_CRIT, "===================5");
return array;
}
Also in java we need to convert the byte[] to int[] in order to get the exact pixel color values which can be done with the help of the following function
public static int byteToColorInt(byte b) {
return b & 0xFF;
}