How to convert an 8-bit OpenCV IplImage* to a 32-bit IplImage*?

Question

I need to convert an 8-bit IplImage to a 32-bits IplImage. Using documentation from all over the web I\'ve tried the following things:

// general code
img2 =         


        

Answer 1

Perhaps this link can help you?

Edit In response to the second edit of the OP and the comment

Have you tried

float value = 0.5

instead of

float value = 0x0000001;

I thought the range for a float color value goes from 0.0 to 1.0, where 1.0 is white.

Answer 2

IplImage *img8,*img32;
img8 =cvLoadImage("a.jpg",1);

    cvNamedWindow("Convert",1);
    img32 = cvCreateImage(cvGetSize(img8),IPL_DEPTH_32F,3);
    cvConvertScale(img8,img32,1.0/255.0,0.0);

//For Confirmation Check the pixel values (between 0 - 1)

    for(int row = 0; row < img32->height; row++ ){
                float* pt = (float*) (img32->imageData + row * img32->widthStep);
                for ( int col = 0; col < width; col++ )
                            printf("\n %3.3f , %3.3f , %3.3f ",pt[3*col],pt[3*col+1],pt[3*col+2]);                  
            }

    cvShowImage("Convert",img32);
    cvWaitKey(0);
    cvReleaseImage(&img8);
    cvReleaseImage(&img32);
    cvDestroyWindow("Convert");

Answer 3

The function you are looking for is cvConvertScale(). It automagically does any type conversion for you. You just have to specify that you want to scale by a factor of 1/255 (which maps the range [0...255] to [0...1]).

Example:

IplImage *im8 = cvLoadImage(argv[1]);
IplImage *im32 = cvCreateImage(cvSize(im8->width, im8->height), 32, 3);

cvConvertScale(im8, im32, 1/255.);

Note the dot in 1/255. - to force a double division. Without it you get a scale of 0.

Answer 4

If you do not put the dot (.), some compilers will understand is as an int division, giving you a int result (zero in this case).

Answer 5

Floating point colors go from 0.0 to 1.0, and uchars go from 0 to 255. The following code fixes it:

// h is height, w is width, c is current channel (0 to 2)
int b = ((uchar *)(img->imageData + h*img->widthStep))[w*img->nChannels + c];
((float *)(img2->imageData + h*img2->widthStep))[w*img2->nChannels + c] = ((float)b) / 255.0;

Many, many thanks to Stefan Schmidt for helping me fix this!

Answer 6

You can create an IplImage wrapper using boost::shared_ptr and template-metaprogramming. I have done that, and I get automatic garbage collection, together with automatic image conversions from one depth to another, or from one-channel to multi-channel images.

I have called the API blImageAPI and it can be found here: http://www.barbato.us/2010/10/14/image-data-structure-based-shared_ptr-iplimage/

It is very fast, and make code very readable, (good for maintaining algorithms)

It is also can be used instead of IplImage in opencv algorithms without changing anything.

Good luck and have fun writing algorithms!!!