> Sent: Monday, May 07, 2018 at 4:41 PM
> From: "Christoph Feck" <cf...@kde.org>
> To: "Jason H" <jh...@gmx.com>, "interestqt-project.org"
> <interest@qt-project.org>
> Subject: Re: [Interest] QImage transformed() background color
>
> On 07.05.2018 21:56, Jason H wrote:
> > I'm rotating some images by non-90 degree amounts, but when I do, the image
> > gets filled with a color value (black) for pixels where there is no image
> > data after rotation, but are in the output image, which causes a problem
> > with later analysis because it trips edge detection. It would be nice to be
> > able to control the fill color, or better yet, not have any fill as a
> > result of the rotate, and just use want's in the image. Ideally, I'd like
> > to pass it a fillColor (Qt::transparent) so that I can just look at the
> > alpha channel and ignore pixels with a 0 alpha. How can I accomplish that
> > if I can't select the color?
> >
> > I don't know that it's possible to select the rotated rectangle out and
> > draw it on a transparent image with a QPainter?
> >
> >
> > QImage rotate(const QImage &image, double degrees){
> > if (degrees > 0.01 || degrees < -0.01) {
> > QTransform tx;
> > QPoint center = image.rect().center();
> > tx.translate(center.x(), center.y());
> > tx.rotate(degrees);
> > return image.transformed(tx, Qt::SmoothTransformation);
> > } else {
> > return image;
> > }
> > }
>
> The rotated image is filled with transparent pixels for ARGB images. You
> can use QPainter compositing to paint that image on any colored
> background (or on your original image).
Ah, so that implies that the image I am working on is not ARGB, just RGB...
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