Save matrix of double values in OpenCV

Question

I have an OpenCV matrix of double (CV_32F) values. I'd like to save it to the disk. I know, I could convert it to an 1-Channel 8-bit IplImage and save it. But that way, I loose precision. Is there a way to save it directly in the 32-bit format, without having to convert it first? It also would be nice, if the resulting file would have an image format, so I can view the result as an image.

Answer 1

You could always iterate over the matrix and write it out yourself. If you want it to be viewable as an image, you can use a variant of PPM. I'm not sure what programs would be able to natively read your image format if you use values out of the 0-255 range though.

Answer 2

You can always save any "object" (CvMat, IplImage, anything..) from OpenCV "as is" by using cvSave() and loading it back with cvLoad(). As to my experience, most floating-point image stuff does not work correctly, I usually save my floating point data this way. However, you cannot directly view the stored data.

Another possibility we have used frequently is including an own built of OpenEXR. You can easily store full precision floating point images using this library and many third party applications are able to open EXR files. Note that OpenCV includes OpenEXR, if i am not mistaken, but the last time i've tried, saving/loading floating point images did not work correctly. However, you should first try to save an fp image as *.exr, maybe that already does the magic with recent versions.