can Qt darker / lighter a image ?

[wesley]

I want to implment a widget to indicate the light status, and I alread have a light image.

Does Qt has ability to darker/lighter a image ? how to do ?

and the image has some transparent area, and alpha channel, is it possible that the result image still have transparent and alpha ?
sorry, i am not familiar with this ...

Tks ...

/WX

[aamer4yu]

From the QImage you can get pixel ( QImage::pixel ) . You can then set the pixel to desired color.QColor::setRgb and use QColor::darker or QColor::lighter .

Other wise you can also have look at QGraphicsEffect and derived classes.

[vishwajeet.dusane]

hi

try this code

QImage *tmpImage = new QImage(SOME_IMAGE_PATH);
    QPoint p1, p2;
    p2.setY(tmpImage->height());
 
    QLinearGradient gradient(p1, p2);
    gradient.setColorAt(0, Qt::transparent);
    gradient.setColorAt(1, QColor(0, 0, 0, 255));
 
    QPainter p(tmpImage);
    p.fillRect(0, 0, tmpImage->width(), tmpImage->height(), gradient);
 
    gradient.setColorAt(0,QColor(0, 0, 0, 255));
    gradient.setColorAt(1, Qt::transparent);
    p.fillRect(0,0, tmpImage->width(), tmpImage->height(), gradient);
 
    p.end();

QImage *tmpImage = new QImage(SOME_IMAGE_PATH);
    QPoint p1, p2;
    p2.setY(tmpImage->height());

    QLinearGradient gradient(p1, p2);
    gradient.setColorAt(0, Qt::transparent);
    gradient.setColorAt(1, QColor(0, 0, 0, 255));

    QPainter p(tmpImage);
    p.fillRect(0, 0, tmpImage->width(), tmpImage->height(), gradient);

    gradient.setColorAt(0,QColor(0, 0, 0, 255));
    gradient.setColorAt(1, Qt::transparent);
    p.fillRect(0,0, tmpImage->width(), tmpImage->height(), gradient);

    p.end();

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You can use this code to darker or lighter the image, depending upon ur requirement change gradient color range.

BTW this is gradient color i have used on the image. you can use plain color as well

[wesley]

Hello, thanks , follow your suggestion， I have below code. and better idea ?

place here for someone may also looking for ...

void do_light_adjust(QImage *image, int factor)
{
	if (image == NULL || image->isNull() || factor == 0)
		return;
 
	int bytes_per_pixel = image->bytesPerLine() / image->width();
	uchar *pixel = NULL;
	QRgb *rgba;
 
	if (factor > 0) { // lighter
		factor += 100;
		for (int h = 0; h < image->height(); h++) {
			pixel = image->scanLine(h);
			for (int w = 0; w < image->width(); w++) {
				rgba = (QRgb *)pixel;
				if (qAlpha(*rgba) != 0 && (qRed(*rgba) != 0 || qGreen(*rgba) != 0 || qBlue(*rgba) != 0))
					*rgba = QColor::fromRgba(*rgba).lighter(factor).rgba();
				pixel += bytes_per_pixel;
			}
		}
	} else { // darker
		factor = -factor;
		factor += 100;
		for (int h = 0; h < image->height(); h++) {
			uchar *pixel = image->scanLine(h);
			for (int w = 0; w < image->width(); w++) {
				rgba = (QRgb *)pixel;
				if (qAlpha(*rgba) != 0 && (qRed(*rgba) != 0 || qGreen(*rgba) != 0 || qBlue(*rgba) != 0))
					*rgba = QColor::fromRgba(*rgba).darker(factor).rgba();
				pixel += bytes_per_pixel;
			}
		}
	}
}

void do_light_adjust(QImage *image, int factor)
{
	if (image == NULL || image->isNull() || factor == 0)
		return;

	int bytes_per_pixel = image->bytesPerLine() / image->width();
	uchar *pixel = NULL;
	QRgb *rgba;

	if (factor > 0) { // lighter
		factor += 100;
		for (int h = 0; h < image->height(); h++) {
			pixel = image->scanLine(h);
			for (int w = 0; w < image->width(); w++) {
				rgba = (QRgb *)pixel;
				if (qAlpha(*rgba) != 0 && (qRed(*rgba) != 0 || qGreen(*rgba) != 0 || qBlue(*rgba) != 0))
					*rgba = QColor::fromRgba(*rgba).lighter(factor).rgba();
				pixel += bytes_per_pixel;
			}
		}
	} else { // darker
		factor = -factor;
		factor += 100;
		for (int h = 0; h < image->height(); h++) {
			uchar *pixel = image->scanLine(h);
			for (int w = 0; w < image->width(); w++) {
				rgba = (QRgb *)pixel;
				if (qAlpha(*rgba) != 0 && (qRed(*rgba) != 0 || qGreen(*rgba) != 0 || qBlue(*rgba) != 0))
					*rgba = QColor::fromRgba(*rgba).darker(factor).rgba();
				pixel += bytes_per_pixel;
			}
		}
	}
}

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