OpenCV-Devel: Fetch color, intensity and texture of an image

[Arun A K]

Hi

I'm new to OpenCV and just started sifting through the APIs. I intend to fetch the color, intensity and texture values of each pixel constituting the image. I was fiddling with the structure - IplImage to start with but couldn't make much progress.

A friend suggested me to try the following snippet-

#include <iostream.h>

#include <math.h>

#include <cv.h>

#include <highgui.h>

int main( int argc, char** argv )

{

// Load the image

    Mat M = imread("..//secondfig.png");

    // Display

    namedWindow("Lena",CV_WINDOW_AUTOSIZE);

    imshow("Lena",M);

    waitKey();  

    // Crop out rectangle from (100,100) of size (200,200) of the red channel 

    const int offset[2] = {100,100};

    const int dims[2] = {200,200};      

    Mat Red(dims[0],dims[1],CV_8UC1);

    // Read it from M into Red

    uchar* lena = M.data;

    for(int i=0;i<dims[0];++i)

        for(int j=0;j<dims[0];++j)

        {

                // P = i*rows*channels + j*channels + c

                Red.at<uchar>(i,j) = *(lena + (i+offset[0])*M.rows*M.channels() + (j+offset[1])*M.channels()+0);

        }

    //Display

    namedWindow("RedRect",CV_WINDOW_AUTOSIZE);

    imshow("RedRect",Red);

    waitKey();

}

I tried to compile it using - g++ test.cpp -o test -I /usr/include/opencv/ -L /usr/local/lib -lm -lcv -lhighgui -lcvaux -Wno-deprecated

and I get the following errors:

test.cpp: In function ‘int main(int, char**)’:

test.cpp:11: error: ‘Mat’ was not declared in this scope

test.cpp:11: error: expected `;' before ‘M’

test.cpp:13: error: ‘namedWindow’ was not declared in this scope

test.cpp:14: error: ‘M’ was not declared in this scope

test.cpp:14: error: ‘imshow’ was not declared in this scope

test.cpp:15: error: ‘waitKey’ was not declared in this scope

test.cpp:20: error: expected `;' before ‘Red’

test.cpp:28: error: ‘Red’ was not declared in this scope

test.cpp:28: error: expected primary-expression before ‘>’ token

test.cpp:33: error: ‘Red’ was not declared in this scope

Is imread() only supported by the latest version of OpenCV?

opencv-devel installed in our labs on RHEL machines. Is there a way to find the version of the installed library?

I would really appreciate any help in this regard.

Thanks for your time and help.

Regards

Arun A K
Graduate Student
Department of Computer Science
Indiana University, Bloomington

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[Nils Hasler-2]

Hi,

all opencv functions are prefixed with cv, and structures with Cv

Mat M = ...
should be
CvMat M = ...

but you probably want to use

IplImage M = cvLoadImage("../secondfig.png");

imread and imshow are matlab functions I believe. they do not exist in opencv.
check out the documentation at
http://opencv.willowgarage.com/documentation/index.html

cheers,
nils

On Saturday 10 October 2009 23:30:31 Arun A K wrote:

> Hi
> I'm new to OpenCV and just started sifting through the APIs. I intend to
> fetch the color, intensity and texture values of each pixel constituting
> the image. I was fiddling with the structure - IplImage to start with but
> couldn't make much progress.
>
> A friend suggested me to try the following snippet-
>
> *#include <iostream.h>*
> *#include <math.h>*
> *#include <cv.h>*
> *#include <highgui.h>*
> *
> *
> *int main( int argc, char** argv )*
> *{*
> *// Load the image*
> *    Mat M = imread("..//secondfig.png");*
> *    // Display*
> *    namedWindow("Lena",CV_WINDOW_AUTOSIZE);*
> *    imshow("Lena",M);*
> *    waitKey();  *
> *
> *
> *    // Crop out rectangle from (100,100) of size (200,200) of the red
> channel *
> *    const int offset[2] = {100,100};*
> *    const int dims[2] = {200,200};      *
> *    Mat Red(dims[0],dims[1],CV_8UC1);*
> *
> *
> *    // Read it from M into Red*
> *    uchar* lena = M.data;*
> *    for(int i=0;i<dims[0];++i)*
> *        for(int j=0;j<dims[0];++j)*
> *        {*
> *                // P = i*rows*channels + j*channels + c*
> *                Red.at<uchar>(i,j) = *(lena +
> (i+offset[0])*M.rows*M.channels() + (j+offset[1])*M.channels()+0);*
> *        }*
> *
> *
> *    //Display*
> *    namedWindow("RedRect",CV_WINDOW_AUTOSIZE);*
> *    imshow("RedRect",Red);*
> *    waitKey();*
> *}*
>
> I tried to compile it using - *g++ test.cpp -o test -I /usr/include/opencv/
> -L /usr/local/lib -lm -lcv -lhighgui -lcvaux -Wno-deprecated*
>
> and I get the following errors:
> test.cpp: In function ‘int main(int, char**)’:
> test.cpp:11: error: ‘Mat’ was not declared in this scope
> test.cpp:11: error: expected `;' before ‘M’
> test.cpp:13: error: ‘namedWindow’ was not declared in this scope
> test.cpp:14: error: ‘M’ was not declared in this scope
> test.cpp:14: error: ‘imshow’ was not declared in this scope
> test.cpp:15: error: ‘waitKey’ was not declared in this scope
> test.cpp:20: error: expected `;' before ‘Red’
> test.cpp:28: error: ‘Red’ was not declared in this scope
> test.cpp:28: error: expected primary-expression before ‘>’ token
> test.cpp:33: error: ‘Red’ was not declared in this scope
>
> Is imread() only supported by the latest version of OpenCV?
> opencv-devel installed in our labs on RHEL machines. Is there a way to find
> the version of the installed library?
>
> I would really appreciate any help in this regard.
>
> Thanks for your time and help.
>
> Regards
> Arun A K
> Graduate Student
> Department of Computer Science
> Indiana University, Bloomington

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[Xavier Delacour]

On Sat, Oct 10, 2009 at 3:50 PM, Nils Hasler <nils.hasler@...> wrote:

> Hi,
>
> all opencv functions are prefixed with cv, and structures with Cv
>
> Mat M = ...
> should be
> CvMat M = ...
>
> but you probably want to use
>
> IplImage M = cvLoadImage("../secondfig.png");
>
> imread and imshow are matlab functions I believe. they do not exist in opencv.
> check out the documentation at
> http://opencv.willowgarage.com/documentation/index.html

No, they are part of the new C++ interface in head (see
{highgui,cv,cxcore,cvaux}.hpp). The cv prefix has also been replaced
with cv namespace.

>> Is imread() only supported by the latest version of OpenCV?
>> opencv-devel installed in our labs on RHEL machines. Is there a way to find
>> the version of the installed library?

Yes, the new interface is only available since quite recently. So
either you should find and install latest packages or build from
sources/svn. The so files should have a suffix w/ version number, eg,
libcv.so.2.0. rpm will also tell you package version.

Xavier

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[Xavier Delacour]

On Sat, Oct 10, 2009 at 2:30 PM, Arun A K <arnkrishn@...> wrote:

> Hi
> I'm new to OpenCV and just started sifting through the APIs. I intend to
> fetch the color, intensity and texture values of each pixel constituting the
> image. I was fiddling with the structure - IplImage to start with but
> couldn't make much progress.
> A friend suggested me to try the following snippet-
> #include <iostream.h>
> #include <math.h>
> #include <cv.h>
> #include <highgui.h>

Also you should add

using namespace cv;

here or prefix Mat and other opencv C++ symbols with cv:: .

Xavier

> int main( int argc, char** argv )
> {
> // Load the image
>     Mat M = imread("..//secondfig.png");
>     // Display
>     namedWindow("Lena",CV_WINDOW_AUTOSIZE);
>     imshow("Lena",M);
>     waitKey();
>     // Crop out rectangle from (100,100) of size (200,200) of the red
> channel
>     const int offset[2] = {100,100};
>     const int dims[2] = {200,200};
>     Mat Red(dims[0],dims[1],CV_8UC1);
>     // Read it from M into Red
>     uchar* lena = M.data;
>     for(int i=0;i<dims[0];++i)
>         for(int j=0;j<dims[0];++j)
>         {
>                 // P = i*rows*channels + j*channels + c
>                 Red.at<uchar>(i,j) = *(lena +
> (i+offset[0])*M.rows*M.channels() + (j+offset[1])*M.channels()+0);
>         }
>     //Display
>     namedWindow("RedRect",CV_WINDOW_AUTOSIZE);
>     imshow("RedRect",Red);
>     waitKey();
> }
> I tried to compile it using - g++ test.cpp -o test -I /usr/include/opencv/
> -L /usr/local/lib -lm -lcv -lhighgui -lcvaux -Wno-deprecated
> and I get the following errors:
> test.cpp: In function ‘int main(int, char**)’:
> test.cpp:11: error: ‘Mat’ was not declared in this scope
> test.cpp:11: error: expected `;' before ‘M’
> test.cpp:13: error: ‘namedWindow’ was not declared in this scope
> test.cpp:14: error: ‘M’ was not declared in this scope
> test.cpp:14: error: ‘imshow’ was not declared in this scope
> test.cpp:15: error: ‘waitKey’ was not declared in this scope
> test.cpp:20: error: expected `;' before ‘Red’
> test.cpp:28: error: ‘Red’ was not declared in this scope
> test.cpp:28: error: expected primary-expression before ‘>’ token
> test.cpp:33: error: ‘Red’ was not declared in this scope
> Is imread() only supported by the latest version of OpenCV?
> opencv-devel installed in our labs on RHEL machines. Is there a way to find
> the version of the installed library?
> I would really appreciate any help in this regard.
> Thanks for your time and help.
> Regards
> Arun A K
> Graduate Student
> Department of Computer Science
> Indiana University, Bloomington
>
> ------------------------------------------------------------------------------
> Come build with us! The BlackBerry(R) Developer Conference in SF, CA
> is the only developer event you need to attend this year. Jumpstart your
> developing skills, take BlackBerry mobile applications to market and stay
> ahead of the curve. Join us from November 9 - 12, 2009. Register now!
> http://p.sf.net/sfu/devconference
> _______________________________________________
> Opencvlibrary-devel mailing list
> Opencvlibrary-devel@...
> https://lists.sourceforge.net/lists/listinfo/opencvlibrary-devel
>
>

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[Wenting]

I'm using this code to crop image,
it works on images in opencv/samples/c/ folder, like lena.jpg, etc.
but it doesn't work on my own jpg files,
some of the cropped results are like missing every other line.
anybody has thoughts??
Thanks very much!