I have written a program that relies on Magick++ simply for importing and exporting of a wide variety of image formats. It uses Image.getPixels() to get a PixelPacket, does a lot of matrix transformations, then calls Image.syncPixels() before writing a new image. The general approach is the same as the example shown in Magick++'s documentation. More or less, the relevant code is:
Magick::Image image("image01.bmp");
image.modifyImage();
Magick::PixelPacket *imagePixels = image.getPixels(0, 0, 10, 10);
// Matrix manipulation occurs here.
// All actual changes to the PixelPacket direct changes to pixels like so:
imagePixels[i].red = 4; // or any other integer
// finally, after matrix manipulation is done
image.syncPixels();
image.write("image01_transformed.bmp");
When I run the above code, the new image file ("image01_transformed.bmp" in this example) ends up being the same as the original. However, if I write it to a different format, such as "image01_transformed.ppm", I get the correct result: a modified image. I assume this is due to a cached version of the format-encoded image, and that Magick++ is for some reason not aware that the image is actually changed and therefore the cache is out of date. I tested this idea by adding image.blur(1.0, 0.1); immediately before image.syncPixels();, and forcing this inconsequential change did indeed result in the correct result for same-format images.
Is there a way to force Magick++ to realize that the cache is out-of-date? Am I using getPixels() and syncPixels() incorrectly in the first place? Thanks!