Question

The CvMat type 16 corresponds to “CV_AA”. Is there an easy conversion between this and the type CV_32F?

Something in the same vein as cvCvtColor(cimg,gimg,CV_BGR2GRAY);?

Answer 1

CV_AA is used for telling drawing functions (i.e., line, circle, fonts, etc) to perform anti-aliased drawing; I don’t believe it is a proper Mat data-type. As you can see in core_c.h, it is defined in the drawing functions section.

Could you show the code where you are receiving this data-type from?

EDIT : I think I see what’s going on 🙂

Given that CV_8U is this:

#define CV_8U   0

And CV_MAKETYPE is:

#define CV_MAKETYPE(depth,cn) (CV_MAT_DEPTH(depth) + (((cn)-1) << CV_CN_SHIFT))

where cn is the number of channels, and CV_CN_SHIFT is 3. I’m betting the type 16 you are seeing is actually

(0 + ((3 - 1) << 3)) -> 16 or AKA CV_8UC3.

So, you have an 8bpp RGB image not a CV_AA image 🙂

You need to convert each channel from CV_8U to CV_32F.

EDIT : Take a look at using cvSplit and cvMerge (I haven’t used the C interface in a while, but it should be something like the following):

IplImage* src = cvCreateImage( size, IPL_DEPTH_8U, 3 ); // CV_8UC3
IplImage* r8u = cvClone(src); 
IplImage* g8u = cvClone(src);
IplImage* b8u = cvClone(src);

IplImage* dst = cvCreateImage( size, IPL_DEPTH_32F, 3 ); // CV_32F
IplImage* r32f = cvClone(dst); 
IplImage* g32f = cvClone(dst);
IplImage* b32f = cvClone(dst);

// split the channels apart...
cvSplit(src, b8u, g8u, r8u, NULL); // assuming in OpenCV BGR order here...may be RGB...

// convert the data...
cvConvertScale(b8u, b32f, 1, 0);
cvConvertScale(g8u, g32f, 1, 0);
cvConvertScale(r8u, r32f, 1, 0);

// merge them back together again if you need to...
cvMerge(r32f, g32f, b32f, NULL, dst);