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

[Dženan Zukić]

Yes, you should report it here: http://public.kitware.com/Bug/

Regards,
Dženan

On Tue, Jun 22, 2010 at 13:39, Aurelien Bricier <aurelien.bricier at c-s.fr>wrote:

> 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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