cv.cornerSubPix: error: (-210) Unexpected Standard exception from MEX file about mexopencv HOT 6 CLOSED

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On Feb 22, 2013, at 12:19, Peugas [email protected] wrote:

I'm trying to use cv.cornerSubPix but I'm having some error:(-210).
I'm using it almost the same way it is used in the camera calibration
sample.

This is my code:
corners_left_ = cv.findChessboardCorners(image_left, [10, 7]);
corners_left = cv.cornerSubPix(image_left, corners_left_);

where image_left is an RGB image (uint8) with the hole chessboard.

Error using cv.cornerSubPix
Unexpected Standard exception from MEX file.
What()
is:/home/tiago/Downloads/OpenCV-2.4.3/modules/imgproc/src/cornersubpix.cpp:70:
error: (-210) The source image must be 8-bit single-channel (CV_8UC1) in
function cvFindCornerSubPix

For me it makes no sense using a single-channel image in cv.cornerSubPix
and looking at the camera calibration sample, it is used an RGB image
(uint8).

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@peugas: you should know that cvFindChessboardCorners internally converts RGB images to grayscale..

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"Send that feature request to OpenCV developers."
I'm not requesting any feature...

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@peugas You're requesting the new feature for cv.cornerSubPix to accept RGB image;)

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Sorry, my bad.
I didn't realized that I was supposed to provide an grayscale image to cv.cornerSubPix.

Maybe it's a good idea to change cv.cornerSubPix help file to something like:
"im: Source chessboard view. It must be an 8­bit grayscale."

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The help description is from the official OpenCV docs.

http://docs.opencv.org/modules/imgproc/doc/feature_detection.html#cornersubpix

Actually, it makes sense to me the function only takes single channel because the definition of corner in this algorithm is defined only up to a single channel (not necessarily grayscale). And the function cannot assume RGB or BGR input if multiple channels are given. It can be any color space.

As for the help description, I can add single-channel requirement. But please keep in mind that the mexopencv api is almost always based on the official OpenCV api.

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