OpenCV convertTo()

Question

I came across this code:

image.convertTo(temp_image,CV_16SC3);

I saw the description of the convertTo() function from here , but what confuses me is image . How can we read the above code? What would be the relation between image and temp_image ?

Thanks.

Answer 1

The other answers here are correct, but lack some details. Let me try.

image.convertTo(temp_image,CV_16SC3);

You have a source image image , and a destination image temp_image . You didn't specify the type of image , but probably is CV_8UC3 or CV_32FC3 , ie a 3 channel image (since convertTo doesn't change the number of channels), where each channel has depth 8 bit ( unsigned char , CV_ 8U C3) or 32 bit ( float , CV_ 32F C3).

This line of code will change the depth of each channel, so that temp_image has each channel of depth 16 bit ( short ). Specifically it's a signed short , since the type specifier has the S : CV_16 S C3.

Note that if you are narrowing down the depth, as in the case from float to signed short , then saturate_cast will make sure that all the values in temp_image will be in the correct range, ie in [–32768, 32767] for signed short .

Why you need to change the depth of an image?

1. Some OpenCV functions require input images with a specific depth.
2. You need a matrix to contain a different range of values. Eg if you need to sum (or subtract) some images CV_8UC3 (tipically BGR images), you'd better store the result in a CV_16SC3 or you'll probably get wrong results due to saturations, since the range for CV_8U images is in [0,255]
3. You read with imread , or want to store with imwrite images with 16bit depth. This are usually used (AFAIK) in medical or graphics application to allow a wider range of colors. However, most monitors do not support 16bit image visualization.
4. There may be other cases, let me know if I miss the one important to you.

Answer 2

An image is a matrix of pixel information (ie a 1080p image will be a 1,920 × 1,080 matrix where each entry contains rbg values for that pixel). All you are doing is reformatting that matrix (each pixel entry, iteratively) into a new type ( CV_16SC3 ) so it can be read by different programs.

The temp_image is a new matrix of pixel information based off of image formatted into CV_16SC3 .

Answer 3

The first one is a source , the second one - destination . So, it takes image, converts it into type CV_16SC3 and stores in temp_image.