Converting a 4 channel matrix to 1 channel in Android using OpenCV

Question

I've created a matrix from a ARGB_8888 bitmap like this:

Mat detectedFaceMat = Utils.bitmapToMat(bmp1);

The resultant matrix has 4 channels. I now need to compare it to 1 channel matrices. Not sure how to convert the 4 channel to 1 (I only need grayscale).

will you use the alpha channel? http://stackoverflow.com/questions/3053889/how-to-convert-32-bit-rgba-image-to-grayscale-preserving-alpha — techiServices, Feb 28 '12 at 22:22

score 2 · Accepted Answer · answered Feb 29 '12 at 13:49

2

OpenCV supports CV_BGRA2GRAY with cv::cvtColor() or cvCvtColor() which converts BGRA pixels to Grey.
It is possible that ARGB is in fact BGRA in memory (this is the most common format). In this case The above conversion will work as expected.

If not, you can always use the green channel as a pretty good approximation for grey.

answered Feb 29 '12 at 13:49

Adi Shavit

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Thanks - exactly what I needed – scoleman2272 Feb 29 '12 at 21:45

Converting a 4 channel matrix to 1 channel in Android using OpenCV

1 Answers1