Kristou Says

Some time we need the image to be in some special range to be useful for some algorithm. In this case I needed my image to be in [0...1] range. I found this helpful piece of code, I tried it and I wanted to share it.

//read in a image
//this will result in a 8bit image [0...255]
IplImage* image_8U = cvLoadImage("test.jpg");

//to change the bit-depth you will have to allocate new memory
IplImage* image_32F = cvCreateImage(cvGetSize(image_8U),IPL_DEPTH_32F,image_8U->nChannels);

//now convert the 8bit Image into 32bit floating points
cvCvtScale(image_8U,image_32F);

//now all your data is stored in float values but in the original scale [0...255]
//to change this you'll have to normalize your matrix

// this will result in an image that is scaled to [0...1] by dividing through the highest value in the array
cvNormalize(image_32F,image32_F,0,1,CV_MINMAX);

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1 – Makefiles and others, that’s are used by the make tool, are generated by building systems. In particular, Qt uses qmake and OpenCV, cmake. And I like more CMake, because are more projects that’s use, then you can give some help and tips easily. Qt Creator supports CMake. More: www.cmake.org

2 – If you include some header from some lib, you needs to link against this lib. An example, you was included highgui.h but not linked against the libhighgui. Another common mistake: you link your program to a lib A that’s
are linked with lib B, and don’t link against B. You’ll probably got a lot of undefined symbols too, since lib A needs things are in B, but you aren’t linking against B.

You can download older version of OpenCV using this link.

Of course, obsolete versions are also there.

As of my experience,
- cvClone makes a copy of the image with respect to the ROI attached.
- cvCloneImage makes a full clone of the image (e.g., a duplicate full size image with its own matching ROI attached) rather than just copying the sub-image identified by the source ROI.
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CvScalar p = cvGet2D(img, y, x);
unsigned char r = p.val[0];
unsigned char g = p.val[1];
unsigned char b = p.val[2];

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