How do I save a file with transparency to a JPEG file without Qt making the transparent color black? I know JPEG doesn't support alpha, and the black is probably just a default "0" value for alpha, but black is a horrible default color.
It seems like this should be a simple operation, but all of the mask and alpha functions I've tried are ignored when saving as JPEG.
image->load("someFile.png"); // Has transparent background or alpha channel image->save("somefile.jpg", "JPG"); // Transparent color is black
I've tried filling the image with white before saving as a JPEG, converting the image to ARGB32 (with 8-bit alpha channel) before saving, and even tried ridiculously slow stuff like:
QImage image2 = image1->convertToFormat(QImage::Format_ARGB32); image2.setAlphaChannel(image1->alphaChannel()); image2.save(fileURI, "JPG", this->jpgQuality; // Still black! See: http://188.8.131.52/qt_black_transparent.png for a visual.
I'd try something like this (i.e., load the image, create another image of the same size, paint the background, paint the image):
QImage image1("someFile.png"); QImage image2(image1.size()); image2.fill(QColor(Qt::white).rgb()); QPainter painter(&image2); painter.drawImage(0, 0, image1); image2.save("somefile.jpg", "JPG");