VIPS image skewed in QT

ademmler

I am trying to load an image with lib vips and display this in Qt.
After loading the image and passing it to QImage - the image is skewed.

Below you can download a minimal code sample and a test image.
Also two screenshots from using vips or qt internal function to load image.

Any hint and help is welcome.
thx in advance Alexander

http://files.lacunasolutions.com/various/VipsMinimal.zip

ademmler

I got help from VIPS maintainer. Here is what did the trick ...

/*
* Hint from vips guy for fixinf skewing:
* In your code, you are using QImage(pointer, width, height, format).
* Perhaps this has assumptions about scanline padding?
* I would try the constructor that lets you set bytesperline as well.
* Use VIPS_IMAGE_SIZEOF_LINE(image.get_image()) to get the line size.
*/

   vipsObject = VImage::new_from_file (imagePath.toStdString().c_str(), VImage::option ()->set ("access", VIPS_ACCESS_SEQUENTIAL));

   imageObject = new QImage();
   *imageObject = QImage((uchar*)vipsObject.data(), vipsObject.width(), vipsObject.height(), VIPS_IMAGE_SIZEOF_LINE(vipsObject.get_image()), QImage::Format_RGB888);
   image = QPixmap::fromImage(*imageObject);

Pl45m4

@ademmler

This looks like an image-type issue. I'm not an expert, when it comes to VIPS (more experience with OCV). but what channel structure do these vip-images have? Is there an alpha channel?

ademmler

I got help from VIPS maintainer. Here is what did the trick ...

/*
* Hint from vips guy for fixinf skewing:
* In your code, you are using QImage(pointer, width, height, format).
* Perhaps this has assumptions about scanline padding?
* I would try the constructor that lets you set bytesperline as well.
* Use VIPS_IMAGE_SIZEOF_LINE(image.get_image()) to get the line size.
*/

   vipsObject = VImage::new_from_file (imagePath.toStdString().c_str(), VImage::option ()->set ("access", VIPS_ACCESS_SEQUENTIAL));

   imageObject = new QImage();
   *imageObject = QImage((uchar*)vipsObject.data(), vipsObject.width(), vipsObject.height(), VIPS_IMAGE_SIZEOF_LINE(vipsObject.get_image()), QImage::Format_RGB888);
   image = QPixmap::fromImage(*imageObject);

SGaist

Hi,

One important thing: there's no need for imageObject to be allocated on the heap. You are likely leaking it with the way you use your code.

ademmler

@SGaist What does this mean in detail?
What should I change?

SGaist

@ademmler said in VIPS image skewed in QT:

imageObject

Make it a simple QImage. No pointers needed.

ademmler

@SGaist thx for the hint.