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how do I copy specific pixels to destination mat from source mat in opencv c++?

asked 2017-11-23 01:33:35 -0500

Explorer_DS gravatar image

updated 2017-11-23 05:40:18 -0500

I want to copy specific pixels to destination mat when certain condition becomes true.in addition to that I a switching to next rows upon specific count of pixels that met condition. But it throws memory related exception as follows:

** Error in `/home/ds/eclipse-workspace/pixelenc_current/Debug/pixelenc_current.so': malloc(): memory corruption (fast): 0x0000000001593710 ***
======= Backtrace: =========
/lib64/libc.so.6(+0x7ab54)[0x7ffff5521b54]
/lib64/libc.so.6(+0x7ddf7)[0x7ffff5524df7]
/lib64/libc.so.6(__libc_malloc+0x4c)[0x7ffff552710c]
/lib64/libstdc++.so.6(_Znwm+0x1d)[0x7ffff5de11bd]
/usr/local/lib/libopencv_highgui.so.3.3(cvNamedWindow+0xda)[0x7ffff649eeca]
/usr/local/lib/libopencv_highgui.so.3.3(_ZN2cv11namedWindowERKNS_6StringEi+0x38)[0x7ffff64957b8]
/home/ds/eclipse-workspace/pixelenc_current/Debug/pixelenc_current.so[0x409af7]
/home/ds/eclipse-workspace/pixelenc_current/Debug/pixelenc_current.so[0x408d16]
/home/ds/eclipse-workspace/pixelenc_current/Debug/pixelenc_current.so[0x405c7e]
/lib64/libc.so.6(__libc_start_main+0xf5)[0x7ffff54c8c05]
/home/ds/eclipse-workspace/pixelenc_current/Debug/pixelenc_current.so[0x401f29]

platform :centos7 +opencv 3.3

code:

unsigned char *input = (unsigned char*)(mask.data);  //mask
unsigned char *imginput = (unsigned char*)(img.data); // source data
int m=0,n=0;
for(i=hinfo[1];i<hinfo[1]+hinfo[3];i++)                 
{
if(hfcnt>=htotalpix)  // max no of pixels 
break;       
int cnt=0;
for(j=hinfo[0];j<hinfo[0]+hinfo[2];j++)
{
valmask=input[mask.cols *i  +j ] ;
if(valmask==255)  /*condition*/
{
patch1.at<Vec3b>(m,n)[0]=imginput[j*img.cols*1 + i*1 + 0];
patch1.at<Vec3b>(m,n)[1]=imginput[j*img.cols*2 + i*2 + 0];
patch1.at<Vec3b>(m,n)[2]=imginput[j*img.cols*2 + i*3 + 0];
hfcnt++;
cnt++;
}
else
continue;
/* to switch to next row in source*/
if(cnt==hinfo[2])
break; 
n++;
}
m++;
}

here are the images extracted using copyTo , in these images there is a area having black pixels which I don't want to copy. That's why I am copying specific pixels.

image description image description

Here is one of the mask I used to extract sub images. Its different one, right now I cannot produce the mask used to extract above images. image description

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Comments

1

what is hinfo and patch1 ?

berak gravatar imageberak ( 2017-11-23 01:58:30 -0500 )edit
1

your code is broken beyond repair. let's simply forget that.

please try to be more explicit on what you're trying to achieve, so we can help you find a high-level solution for it.

again, writing for-loops like above is always the wrong idea, and you're the umpteeth person shooting his foot like that

berak gravatar imageberak ( 2017-11-23 02:13:36 -0500 )edit

Exception is in name cvNamedWindow. Where is cvNamedWindow in your code?

Why do you write :

patch1.at<Vec3b>(m,n)[0]=imginput[j*img.cols*1 + i*1 + 0];
patch1.at<Vec3b>(m,n)[0]=imginput[j*img.cols*2 + i*2 + 0];
patch1.at<Vec3b>(m,n)[0]=imginput[j*img.cols*2 + i*3 + 0];

last line is enough

You use mask.cols i I understand i is a row index... and imginput[jimg.cols*1 now j is a row index ?

LBerger gravatar imageLBerger ( 2017-11-23 02:13:53 -0500 )edit

^^ imshow() calls namedWindow(), which calls cvNamedWindow()

berak gravatar imageberak ( 2017-11-23 02:26:08 -0500 )edit

I want to copy specific pixels from 3 channel matrix to another matrix. Path1 is also 3 channel matrix of same type as of img. its 0,1,2 in patch1.at<vec3b>(m,n)[0].... valmask used in condition checking to check whether that specific pixel is a part of mask or not hinfo[] contains lower and upper bounds of for loop

once copy is completed I am trying to disply patch1 as follows; namedWindow("patch1", CV_WINDOW_AUTOSIZE ); imshow( "patch1", patch1);

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 02:31:35 -0500 )edit

I am trying to copy only masked pixels to another patch of same type as of source matrix which is img.

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 02:34:08 -0500 )edit

I tried with following code too, but same exception

patch1.at<vec3b>(m,n)=img.at<vec3b>(i.j);

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 02:40:32 -0500 )edit

please do not try to "repair" this code.

berak gravatar imageberak ( 2017-11-23 03:10:56 -0500 )edit

instead of understanding the problem and getting to the solution people are down voting the question


Explorer_DS gravatar imageExplorer_DS ( 2017-11-28 06:18:57 -0500 )edit

1 answer

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answered 2017-11-23 02:40:25 -0500

berak gravatar image

updated 2017-11-23 05:25:14 -0500

so the answer is: use copyTo() with a mask (and a roi):

Rect roi = // something based on hinfo
img(roi).copyTo(patch1, mask);

please try to use opencv's builtin functions, not to defeat it writing ill fated for-loops, like above !

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Comments

it will copy whole square or rectangular shaped ROI , What I want to copy is specific region masked within that ROI.

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 03:01:40 -0500 )edit
1

that's what the mask should be for, no ?

berak gravatar imageberak ( 2017-11-23 03:09:50 -0500 )edit

copyTO will copy entire x +w , y+height that contains min_x, min_y, max_x, max_y coordinates of mask region. my mask is in polygonal shape so I just want to copy pixels that are part of polygon.

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 05:02:33 -0500 )edit

you need a (black)mask in the same size of the roi, you want to copy, and that should contain a (filled ?) white polygon

berak gravatar imageberak ( 2017-11-23 05:16:38 -0500 )edit

I already did that, in fact above images are extracted using polygonal mask that has white portion which marks area to be copied. Now what I want is to copy some pixels from these images to new matrix one by one.

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 05:24:42 -0500 )edit

show your mask, then.

berak gravatar imageberak ( 2017-11-23 05:25:42 -0500 )edit

After copyTo I have cropped images to avoid extra processing

Explorer_DS gravatar imageExplorer_DS ( 2017-11-23 05:43:41 -0500 )edit
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Asked: 2017-11-23 01:33:35 -0500

Seen: 730 times

Last updated: Nov 28 '17