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).
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