Use asift on Android to achieve more robust feature matching for visual changes

This article from http://blog.csdn.net/hellogv/, reference must indicate the source!

This evening is Christmas Eve, with manyFour-Eye technology houseIn the same way, we have a holiday with the computer ......

I explained how to use ndk to convert a color image to a grayscale image on Android. Now I can port the asift example of Windows Mobile to Android ....... here, I would like to thank Jean-micel Morel and guoshen Yu for their selfless dedication and respect for knowledge and the Open Source spirit.

Let's take a look at the program running in this article:

 

The picture on the left shows the result with the lowest recognition rate and the picture on the right shows the result with a low recognition rate.

The code for this article can be downloaded here: http://www.pudn.com/downloads314/sourcecode/comm/android/detail1391871.html

Here, asift's ndk code (C ++) is roughly the same as the DLL code in WM, but there are some differences:

1. JNI does not support reference transfer, so some values must be returned through the function, for example:

/** <Br/> * obtain the enlarged/reduced image size <br/> */<br/> jniexport jintarray jnicall java_com_testasift_libasift_getzoomsize (<br/> jnienv * ENV, jobject OBJ) {<br/> jint arrint [2]; <br/> arrint [0] = im_x; <br/> arrint [1] = im_y; <br/> jintarray result = env-> newintarray (2); <br/> env-> setintarrayregion (result, 0, 2, arrint); <br/> return result; <br/>}< br/>/** <br/> * return the size of the matched image. jintarray [0] is width, jintarray [1] is height <br/> */<br/> jniexport jintarray jnicall java_com_testasift_libasift_getmatchedimagesize (<br/> jnienv * ENV, jobject OBJ) {<br/> jint arrint [2]; <br/> arrint [0] = Wo; <br/> arrint [1] = Ho; <br/> jintarray result = env-> newintarray (2); <br/> env-> setintarrayregion (result, 0, 2, arrint); <br/> return result; <br/>}

2. asift receives an 8-bit grayscale image. Before use, it must be converted to an 8-bit grayscale image:

Void pixeltovector (jint * cbuf, int W, int H, STD: vector <float> * ipixels) {<br/> for (INT I = 0; I <p; I ++) {<br/> for (Int J = 0; j <W; j ++) {<br/> // obtain the pixel color <br/> int color = cbuf [w * I + J]; <br/> int Red = (color & 0x00ff0000)> 16); <br/> int Green = (color & 0x0000ff00)> 8 ); <br/> int Blue = color & 0x000000ff; <br/> color = (Red + green + blue)/3; <br/> ipixels-> push_back (color ); // Save the grayscale value <br/>}< br/>

After use, convert the 8bit grayscale image into rgb565:

Jintarray result = env-> newintarray (WO * Ho); <br/> jint * cresult; <br/> cresult = env-> getintarrayelements (result, false ); <br/> int alpha = 0xff <24; <br/> for (INT I = 0; I <Ho; I ++) {<br/> for (Int J = 0; j <wo; j ++) {<br/> // obtain the pixel color <br/> int color = (INT) opixelsasift [wo * I + J]; <br/> color = Alpha | (color <16) | (color <8) | color; <br/> cresult [wo * I + J] = color; <br/>}< br/> env-> releaseintarrayelements (result, cresult, 0 );

The logic code of the main class testasift. Java is as follows:

Public class testasift extends activity {<br/>/** called when the activity is first created. */<br/> imageview imgview; <br/> @ override <br/> Public void oncreate (bundle savedinstancestate) {<br/> super. oncreate (savedinstancestate); <br/> setcontentview (R. layout. main); <br/> This. settitle ("use asift --- hellogv on Android"); <br/> imgview = (imageview) This. findviewbyid (R. id. imageview01); </P> <p> libasift. initzoomsize (320,480); // scale the target size <br/> int [] size = libasift. getzoomsize (); // determines whether the setting is successful <br/> log. E (string. valueof (size [0]), String. valueof (size [1]); </P> <p> bitmap img1 = (bitmapdrawable) getresources (). getdrawable (R. drawable. adam1 )). getbitmap (); <br/> int W1 = img1.getwidth (), H1 = img1.getheight (); <br/> int [] pix1 = new int [W1 * H1]; <br/> img1.getpixels (pix1, 0, W1, 0, 0, W1, H1); <br/> // extract the features of the first image <br/> libasift. initimage1 (pix1, W1, H1, 2); <br/> bitmap img2 = (bitmapdrawable) getresources (). getdrawable (R. drawable. adam2 )). getbitmap (); <br/> int W2 = img2.getwidth (), H2 = img2.getheight (); <br/> int [] pix2 = new int [W2 * H2]; <br/> img2.getpixels (pix2, 0, W2, 0, 0, W2, H2); <br/> int [] imgpixels = libasift. match2imageforimg (pix2, W2, H2, 2); // match the two graphs <br/> int [] imgsize = libasift. getmatchedimagesize (); // size of the matching result graph <br/> bitmap imgresult = bitmap. createbitmap (imgsize [0], imgsize [1], config. rgb_565); <br/> imgresult. setpixels (imgpixels, 0, imgresult. getwidth (), 0, 0, imgresult. getwidth (), imgresult. getheight (); <br/> imgview. setimagebitmap (imgresult); // display the result </P> <p >}< br/>}