[Interest] QImage + pixel lambdas

Jason H jhihn at gmx.com
Fri Jun 1 15:38:03 CEST 2018


So I'm doing some qimage analysis/manipulation. I think it would be really good if QImage came with a per-pixel function. (Examples below)
I'm tired of writing the x/y for loops. The really neat thing (not in the examples) is using QImage::scanLine(int y) for faster access, and automatically choosing the value of p in the lambda based on bit depth. 

Anyone else think this is a good idea?

//Really sorry about this SFINAE
template <typename T, typename std::enable_if<std::is_same<void, decltype(std::declval<T>()(1))>::value, int>::type = 0>
void eachPixel(const QImage &image, T pixelFunc, const QRect &bounds=QRect()) {
	QRect imageRect(QRect(0,0, image.width(), image.height()));
	QRect region = bounds.isNull() ? imageRect : bounds.intersected(imageRect);

	for (int y=region.y(); y<=region.bottom(); y++) {
		for (int x=region.x(); x<=region.right(); x++) {
			pixelFunc(image.pixel(x,y));
		}
	}
}

//Really sorry about this SFINAE too. 
template <typename T, typename std::enable_if<std::is_same<uint, decltype(std::declval<T>()(1))>::value, int>::type = 0>
QImage eachPixel(const QImage &image, T pixelFunc, const QRect &bounds=QRect()) {
	QRect imageRect(QRect(0,0, image.width(), image.height()));
	QRect region = bounds.isNull() ? imageRect : bounds.intersected(imageRect);

	QImage out(image.size(), image.format());
	for (int y=region.y(); y<=region.bottom(); y++) {
		for (int x=region.x(); x<=region.right(); x++) {
			out.setPixel(x,y, pixelFunc(image.pixel(x,y)));
		}
	}
	return out;
}

void test_pixelFunc() {
	QImage image(300,200, QImage::Format_ARGB32);
	image.fill(Qt::blue);

	QImage out = eachPixel(image, [] (uint p)  {
		return qRgb(qRed(p), qBlue(p), qGreen(p)); // swap green and blue channels 
	}, QRect (5,5, 300, 200));                         // for a portion of the image
	out.save("test_pixelfunc.png");


	int accumulator=0;
        int min = 255;
        int max = 0
	eachPixel(image, [&accumulator, &min, &max](uint p) {         // This one can be used for statistics,
		accumulator +=p;                                      // if you're not making a new image
                if (p < min) min = p;
                if (p > max) max = p;
	}, QRect (5,5, 300, 200));
	qDebug() << "accumulator" << accumulator << "min" << min << "max" << max;

}



More information about the Interest mailing list