How to permanently scale an ImageMagick++ image on Ubuntu? - c++

Question

I have an ImageMagick++ image that I'd like to scale to whatever width and height I like, and then I'd like to get access to the pixels of this new scaled image.
I want the scale operation to permanently alter the image. So far there are four ImageMagick++ methods that sound like they might achieve this scaling operation: resize(), sample(), scale(), and transform(), but the only one that I can get to almost work is sample().
The problem is that when I call tMyImage.sample() and then read the pixel values, the image is only scaled to the height that I pass to it and then the width is set according to the original aspect ratio.
Here's the code I'm using:
Magick::Image tMyIMage(iOriginalWidth, iOriginalHeight, "BGRA", Magick::CharPixel, (void *)pSourceData);
try { tImage.sample(Magick::Geometry(200, 50, 0, 0)); }
catch { Magick::Exception &eException)
{
// This never happens...
}
tImage.modifyImage();
size_t nNewWidth = tImage.columns();
size_t nNewHeight = tImage.rows();
// At this point I would expect that nNewWidth is 200 and nNewHeight is 50
// Instead, nNewHeight is 50 but nNewWidth is scaled according to the original aspect ratio
// Note here that tImage.baseColumns() and tImage.baseRows() both return 0
tImage.type(Magick::TrueColorType);
const Magick::PixelPacket *pPixels = tImage.getConstPixels(0, 0, nNewWidth, nNewHeight);
// Here I would expect that pPixels points to pixel data of a 200x50 pixel image
I am new to ImageMagick++ so I'm sure that I must be doing something wrong. Any help is greatly appreciated! Thanks!

Answer 1

I found out the reason that the scaling wasn't working; apparently the default in ImageMagick++ is to not take the exact dimensions you're using if the resulting aspect ratio would change -_-
You have to explicitly tell ImageMagick++ to take the exact dimensions when creating the geometry:
char szGeometry[64];
memset(&(szGeometry[0]), 0, sizeof(szGeometry));
snprintf(szGeometry, sizeof(szGeometry) - 1, "%ix%i!", iWidth, iHeight);
Magick::Image tScaled(iOriginalWidth, iOriginalHeight, "BGRA", Magick::CharPixel, (void *)pSourceData);
try { tScaled.sample(Magick::Geometry(szGeometry)); }
catch (Magick::Exception &eException)
{
...
}