如何在Qimage中设置像素并保存更改

Question

I want change some colors of pixels and save changes, but not working. I have this loop. First I print on screen true value: like 255,173..., and second cout print on screen zeros. Until here is good.

for (int i = 0; i < image->width(); i++) {
            for (int j = 0; j < image->height(); j++) {

                QRgb pixelData = image->pixel(i,j);
                int red = qRed(pixelData);
                cout<<red<<endl;
                image->setPixel(i, j, qRgb(0, 0, 0));
                pixelData = image->pixel(i,j);
                int red2 = qRed(pixelData);
                 cout<<red2<<endl;
            }
        }

After this loop I saved image. When I reopen or read this image. I got default values.

if (image->save(out.c_str())) {
            std::cout << "save successful!" <<out<<std::endl;
}

Path is good. So I think setPixel not work for save function? How can I fix that?

Answer 1

You have problems with save/load, not with setPixel. May be you need to specify a format while saving, for example:

image.save("somefile.jpg", "JPG");

Answer 2

Problem is saving in JPG. Somehow this format change values and try making file smaller. I saving in PNG and my values stay like I want.

image.save("somefile.png", "PNG");