Image contrast

[toutarrive]

Hello,

i must implement a brightness/contrast filter.

So far I've managed to brighten an image as follows :

QImage ConvolutionFilter:: brighten(QImage& source, int factor)
{
	if (factor < -255 || factor > 255) return source;
	int red, green, blue;
 
	/* for ( int y=0; y<source.height(); y++ ) { 
            uchar *p = source.scanLine(y);
            for (int x = 0; x < source.width(); x ++) {
		red = int((*p++) + factor);
		red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
                green = int((*p++)+ factor);
		green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
                blue = int((*p++) + factor);
		blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
                int alpha = int(*p++);
                QRgb rgbaValue = qRgba(red,green,blue, alpha);
				source.setPixel(x,y, rgbaValue);
				}	
		}*/
 
    int pixels = source.width() * source.height();
    unsigned int *data = (unsigned int *)source.bits();
    for (int i = 0; i < pixels; ++i) {
        red= qRed(data[i])+ factor;
	red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
	green= qGreen(data[i])+factor;
	green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
	blue= qBlue(data[i])+factor;
	blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
        data[i] = qRgba(red, green, blue, qAlpha(data[i]));
    }
    return source;
}

QImage ConvolutionFilter:: brighten(QImage& source, int factor)
{
	if (factor < -255 || factor > 255) return source;
	int red, green, blue;

	/* for ( int y=0; y<source.height(); y++ ) { 
            uchar *p = source.scanLine(y);
            for (int x = 0; x < source.width(); x ++) {
		red = int((*p++) + factor);
		red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
                green = int((*p++)+ factor);
		green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
                blue = int((*p++) + factor);
		blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
                int alpha = int(*p++);
                QRgb rgbaValue = qRgba(red,green,blue, alpha);
				source.setPixel(x,y, rgbaValue);
				}	
		}*/

    int pixels = source.width() * source.height();
    unsigned int *data = (unsigned int *)source.bits();
    for (int i = 0; i < pixels; ++i) {
        red= qRed(data[i])+ factor;
	red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
	green= qGreen(data[i])+factor;
	green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
	blue= qBlue(data[i])+factor;
	blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
        data[i] = qRgba(red, green, blue, qAlpha(data[i]));
    }
    return source;
}

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But I'm totally stuck with contrast.

I would deeply appreciate if someone could give me some hints how to handle this task.

Regards.

[toutarrive]

for those interested i came up with this code, the contrast can be applied recursively :

QImage ConvolutionFilter::contrast(QImage& source, int factor)
{
	//contrast :new color = 128 + Contrast *( old color - 128)
	if (factor < 0) return source;
	if (factor >  20) return source;
	double contrast = (100.0+factor)/100.0;
	double red, green, blue;
	int pixels = source.width() * source.height();
    unsigned int *data = (unsigned int *)source.bits();
    for (int i = 0; i < pixels; ++i) {
		red= 128+ contrast*(qRed(data[i])-128);
		red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
		green= 128+ contrast*(qGreen(data[i])-128);
		green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
		blue= 128+ contrast*(qBlue(data[i])-128);
		blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
		data[i] = qRgba(red, green, blue, qAlpha(data[i]));
    }
    return source;
}

QImage ConvolutionFilter::contrast(QImage& source, int factor)
{
	//contrast :new color = 128 + Contrast *( old color - 128)
	if (factor < 0) return source;
	if (factor >  20) return source;
	double contrast = (100.0+factor)/100.0;
	double red, green, blue;
	int pixels = source.width() * source.height();
    unsigned int *data = (unsigned int *)source.bits();
    for (int i = 0; i < pixels; ++i) {
		red= 128+ contrast*(qRed(data[i])-128);
		red = (red < 0x00) ? 0x00 : (red > 0xff) ? 0xff : red;
		green= 128+ contrast*(qGreen(data[i])-128);
		green = (green < 0x00) ? 0x00 : (green > 0xff) ? 0xff : green;
		blue= 128+ contrast*(qBlue(data[i])-128);
		blue =  (blue  < 0x00) ? 0x00 : (blue  > 0xff) ? 0xff : blue ;
		data[i] = qRgba(red, green, blue, qAlpha(data[i]));
    }
    return source;
}

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Comments and improvements are welcome ...