FreeType::putText write to 4 channels Mat (BGRA)

[xamix]

Hello,

I need some feedback about an Assert used in freetype module of OpenCv:

System information (version)

• OpenCV => 3.4.5-dev
• Operating System / Platform => Windows 64 Bit
• Compiler => Visual Studio 2017

Detailed description

I have a Mat which is created with BGRA data layout -> CV_8UC(4).
I need to write some special text on it and so I cannot use cv::putText.
So I used the function FreeType2::putText

However the Assert at line 196 in freetype.cpp is triggering because my image has 4 channels
but the code seem to handle only 3 channels:
https://github.com/opencv/opencv_contrib/blob/3.4/modules/freetype/src/freetype.cpp#L196

I tested to remove the test to check number of channels and all seem good as far as I know (text seem to be drawn correctly):

CV_Assert( ( _img.empty()    == false ) &&
               ( _img.isMat()    == true  ) &&
               ( _img.depth()    == CV_8U ) &&
               ( _img.dims()     == 2     ) /*&&
               ( _img.channels() == 3     )*/ );

So my question is:
Is there any reason to limit FreeType2::putText function only to RGB image i.e channels = 3 but not channels = 4?, For example the cv::putText function works on both RGB and RGBA image.

Regards

[kalrey]

em~~
I am faced with the same problem. This solution is still work good？did you find any better way to work?

[kalrey]

@xamix

[xamix]

I have not found another solution to this.
It seem to work as far as I know.

But since I was using this to get fixed size character set, I decided to generate a raster image and skip using FreeType contrib for the moment, I'm still waiting answer for the question....

[alalek]

Relaxing check is not enough, need to extend implementation too (search for code with Vec3b):

• Vec3b access pattern

Also there are bad news - no tests for this module.

[kalrey]

I have viewed the code about putTextBitmapMono.I think it’s not necessary to extend implementation of 4 channels.
In fact, 'putTextBitmapMono' just draw the text to a bitmap and then copy it to dst mat. The copying operation is a assignment of B,G,R channel one by one.