Menu
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
204
The QPixmap class is an off-screen image representation that can be used as a paint device. The QImage class provides a hardware-independent image representation that allows direct access to the pixel data, and can be used as a paint device.
A QPixmap object can be converted into a QImage using the toImage() function. Likewise, a QImage can be converted into a QPixmap using the fromImage(). If this is too expensive an operation, you can use QBitmap::fromImage() instead.
There isn't a widget specifically made for displaying images, but this can be done with the label widget. We do this with the pixmap property. QPixmap pic("/path/to/your/image"); ui->label->setPixmap(pic);
Since you use QPixmap, you can use its copy method and supply it with a QRect to perform the actual crop. Show activity on this post. Just use of the QPixmap's copy() functions.
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);
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
