[Insight-users] Cannot read a RGBA png file into itk::Image<unsigned char, 2> properly

[Aurelien Bricier]

Hello ITK users,

I tried to read a 4 channels (RGBA) png image file into an
itk:Image<unsigned char, 2> and the output image makes no sense. It
appears that it works fine with RGB png images. In fact, I located the
issue in ConvertPixelBuffer::ConvertRGBAToGray() that computes the
grayscale pixel value by applying the following formula:

((2125.0 * static_cast<double>RedPixelValue +
   7154.0 * static_cast<double>GreenPixelValue +
   0721.0 * static_cast<double>BluePixelValue)/1000.0)        //OK
      * static_cast<double>AlphaPixelValue
//Here is the issue

In a RGBA png image, the range of AlphaPixelValue is [0,255]. The
resulting grayscale value is no longer reasonably allowed to be casted
into an unsigned char. That's why the reader output doesn't make any
sense. I isolated this behavior in the attachment. Is there another
place where I should report this bug?

Regards,
Aurelien.

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