Mat from width*height*4 bytes BGRA Buffer [closed]

asked 2016-04-24 07:51:21 -0500

Hey guys.

Instead of wasting more time I decided to ask those people who already know a nice answer to my question ; )

I'm using the Chromium Embedded Framework off-screen rendering which provides me an image-buffer which I want to convert to an cv::Mat. According to CEFs docs: "On Windows the buffer will be widthheight4 bytes in size and represents a BGRA image with an upper-left origin." The programming language used is C++.

Unfortunately my basic OpenCV knowledge is not strong enough to convert the buffer properly. With the following code I just get some awkward results saving the Mat.

// Convert the buffer from "const void" to "unsigned char":
unsigned char* buffer = (unsigned char*)cef_buffer_data;
// Buffer to Mat:
cv::Mat image(cef_buffer_height, cef_buffer_width, CV_8UC3, buffer);
// Write Mat to file:
imwrite("image.jpg", image);

Fortunately I'm able to convert my cef_buffer to an hbitmat and save it as an reference. The following Image is what I get by saving the hbitmat and the second one is what I get saving the Mat.

image description

image description

Hopefully someone knows how to fix this. Thanks in advance!

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Closed for the following reason the question is answered, right answer was accepted by DoctorJohn
close date 2016-04-24 08:00:12.809125



CV_8UC3 == 3 8bit channels (your input has 4 of them, so try CV_8UC4 instead)

berak gravatar imageberak ( 2016-04-24 07:53:16 -0500 )edit

Turned a 3 to 4, problem solved. Thanks a lot!

DoctorJohn gravatar imageDoctorJohn ( 2016-04-24 07:59:14 -0500 )edit

oh, cool.

just saying, careful here, this is "borrowed memory".

maybe the 1st thing you want to do is convert it to a "deep" copy

Mat bgr;
cvtColor(image, bgr, COLOR_BGRA2BGR); // CV_8UC3 output now.
// use bgr Mat instead image.
berak gravatar imageberak ( 2016-04-24 08:28:42 -0500 )edit

Well, that's what I started searching for one minute ago. I need to somehow remove the alpha channel anyway for template matching... I guess you brought me the solution right away! Again thanks a lot!

DoctorJohn gravatar imageDoctorJohn ( 2016-04-24 08:36:14 -0500 )edit