Converting colored image to black-white image

depecheSoul

Hello.

I am trying to make a simple program that converts colored images to black-white images.

So far I have made this.

@
void ObradaSlike::convert_picture_to_bw()
{
QImage image;
image.load(fileModel->fileInfo(listView->currentIndex()).absoluteFilePath());

QSize sizeImage = image.size();
int width = sizeImage.width(), height = sizeImage.height();

QRgb color;
int value;

for (int f1=0; f1<width; f1++) {
    for (int f2=0; f2<height; f2++) {
        color = image.pixel(f1, f2);
        image.setPixel(f1, f2, QColor((qRed(color) + qGreen(color) + qBlue(color))/3).rgb());
    }
}
sceneGraphics->clear();
sceneGraphics->addPixmap(QPixmap::fromImage(image));

}
@
I think the code should work, but there is a problem.

The problem with this code is that I always get blue-black images insted black-white images. Do you know how to fix this.

Thanks.

mlong

Be aware that just averaging R, G, and B doesn't lead to a very nice gray scale conversion. (You're not doing that properly either, given the blue/black thing.) You should use QColor's non-member "qGray()":http://qt-project.org/doc/qt-4.8/qcolor.html#qGray-2 function to give you the gray value you're looking for.

You could replace lines 14 and 15 above with
@
color = image.pixel(f1,f2);
image.setPixel(f1,f2, qGray(color));
@

depecheSoul

I have tried what have you suggested mlong, but I am still getting blue-black images.

Thanks.

depecheSoul

Here is the solution:
@
int gray = (qRed(color) + qGreen(color) + qBlue(color))/3;
image.setPixel(f1, f2, qRgb(gray, gray, gray));
@

or

@
int gray = qGray(color);
image.setPixel(f1, f2, qRgb(gray, gray, gray));
@

mlong

Ah, of course. I was thinking that qGray() returned a QRgb value. (I directed you to the docs, but didn't read them, myself, apparently.)

Glad you got it working.

Be sure and edit the original post to add [Solved] to the title. Thanks!

Chesterton WORD

Before you work out your own code, why don't you see some others" template code or image processing software":http://www.rasteredge.com/dotnet-imaging/image-convert/.

andre

[quote author="Chesterton WORD" date="1361957470"]Before you work out your own code, why don't you see some others" template code or image processing software":http://www.rasteredge.com/dotnet-imaging/image-convert/.[/quote]

How does one integrate this .net application with a cross-platform Qt application exactly?