Question

I am building a QT GUI application and use QImage for opening images.
My problem is that I can’t figure out how to use QImage’s bit() and scanline()
methods to get access at per pixel level.

I’ve seen this post Qt QImage pixel manipulation problems
but this is only for the first pixel of each row. Is this correct or I got it all wrong?

thanks in advance

Answer 1

The scanlines correspond to the the height of image, the columns correspond to the width of the image.

According to the docs, the prototype looks like uchar* QImage::scanline(int i), or a similar const version.

But, as a commenter pointed out, because the data is dependent on the machine architecture and image, you should NOT use the uchar * directly. Instead, use something like the following:

QRgb *rowData = (QRgb*)img.scanLine(row);
QRgb pixelData = rowData[col];
int red = qRed(pixelData);