Specify filter for wand.image.distort

[ansstuff]

Some ImageMagick docs recommend using "Distort Resize" instead of simple "Resize" for higher quality slower resizing.

With commandline IM it's simple:
magick.exe input.png -filter Lanczos -distort Resize 200x200! output.png

But with Wand you can only specify filter for wand.image.resize(), but not for wand.image.distort()

inputImage.distort("resize", (newWidth, newHeight))
This uses default filter. And I couldn't find any way to specify global filter in Wand API. Is it perhaps an omission?

[emcconville]

You would achieve this by defining the filter option before calling the distort method.

with Image(...) as inputImage:
    inputImage.options['filter'] = 'lanczos'
    inputImage.distort('resize', (newWidth, newHeight))

The C-API also doesn't have a clear way to mimic the CLI example, but we can update Wand's Distortion Guide to include examples. I think interpolate and filter are the only two previously set options that can impact distortion.

[emcconville]

So there's no way to do it without CLI?

You would have to hack together a solution that uses MagickCore library methods. Wand & other language bindings integrate with MagickWand library, which is the public C-API. I'll post another answer with a working example, but it wouldn't be included in any Wand release until MagickWand publicly offers this feature / behavior.

Sounds like a bug. Should it be posted as an issue here?

You're free to open an issue. It wouldn't be a bug, but rather a request to implement the following methods.

FilterType MagickGetImageFilter(MagickWand *wand);
MagickBooleanType MagickSetImageFilter(MagickWand *wand, FilterType filter);

[emcconville]

Here's a work around. Use at your own risk.

from wand.api import libmagick, library
from wand.image import Image
import ctypes

libmagick.AcquireImageInfo.argtypes = []
libmagick.AcquireImageInfo.restype = ctypes.c_void_p
libmagick.CloneImageInfo.argtypes = [ctypes.c_void_p]
libmagick.CloneImageInfo.restype = ctypes.c_void_p
libmagick.DestroyImageInfo.argtypes = [ctypes.c_void_p]
libmagick.DestroyImageInfo.restype = ctypes.c_void_p
libmagick.SyncImageSettings.argtypes = [ctypes.c_void_p,
                                        ctypes.c_void_p,
                                        ctypes.c_void_p]
libmagick.SyncImageSettings.restype = ctypes.c_bool
libmagick.SetImageOption.argtypes = [ctypes.c_void_p,
                                     ctypes.c_char_p,
                                     ctypes.c_char_p]
libmagick.SetImageOption.restype = ctypes.c_bool


class NeuImage(Image):
    def distort(self, method, arguments, best_fit=False, filter=None):
        if filter is not None:
            image_ptr = library.GetImageFromMagickWand(img.wand)
            image_info_ptr = libmagick.AcquireImageInfo()
            exception_ptr = libmagick.AcquireExceptionInfo()
            libmagick.SetImageOption(image_info_ptr, b"filter", f.encode())
            ok = libmagick.SyncImageSettings(image_info_ptr,
                                             image_ptr,
                                             exception_ptr)
            if not ok:
                raise RuntimeError("Unable to sync ImageInfo.")
            image_info_ptr = libmagick.DestroyImageInfo(image_info_ptr)
            exception_ptr = libmagick.DestroyExceptionInfo(exception_ptr)
        super(NeuImage, self).distort(method, arguments, best_fit)

[ansstuff]

You're free to open an issue. It wouldn't be a bug, but rather a request to implement the following methods.

Yes, not a bug per se, I just assumed feature parity between CLI IM and MagickWand at least for these widespread operations.
Here I've created the issue, is it correct?

What are the risks of this workaround?

[ansstuff]

from wand.api import libmagick, library
from wand.image import Image
import ctypes

libmagick.AcquireImageInfo.argtypes = []
libmagick.AcquireImageInfo.restype = ctypes.c_void_p
libmagick.CloneImageInfo.argtypes = [ctypes.c_void_p]
libmagick.CloneImageInfo.restype = ctypes.c_void_p
libmagick.DestroyImageInfo.argtypes = [ctypes.c_void_p]
libmagick.DestroyImageInfo.restype = ctypes.c_void_p
libmagick.SyncImageSettings.argtypes = [ctypes.c_void_p,
                                        ctypes.c_void_p,
                                        ctypes.c_void_p]
libmagick.SyncImageSettings.restype = ctypes.c_bool
libmagick.SetImageOption.argtypes = [ctypes.c_void_p,
                                     ctypes.c_char_p,
                                     ctypes.c_char_p]
libmagick.SetImageOption.restype = ctypes.c_bool


class NeuImage(Image):
    def distort(self, method, arguments, best_fit=False, filter=None):
        if filter is not None:
            image_ptr = library.GetImageFromMagickWand(self.wand)
            image_info_ptr = libmagick.AcquireImageInfo()
            exception_ptr = libmagick.AcquireExceptionInfo()
            libmagick.SetImageOption(image_info_ptr, b"filter", filter.encode())
            ok = libmagick.SyncImageSettings(image_info_ptr,
                                             image_ptr,
                                             exception_ptr)
            if not ok:
                raise RuntimeError("Unable to sync ImageInfo.")
            image_info_ptr = libmagick.DestroyImageInfo(image_info_ptr)
            exception_ptr = libmagick.DestroyExceptionInfo(exception_ptr)
        super(NeuImage, self).distort(method, arguments, best_fit)

Okay, this works! Thank you for the help! I'd still like to learn about possible issues of this workaround, though. But since I'm only using it for personal projects, I'll stick to this workaround until MagicWand API updates. Not sure if I should press "Mark as answer" until then, since the case isn't closed.

[emcconville]

What are the risks of this workaround?

For home project & academic work, not really. If a script crashes, it would be isolated to you. Putting the work around in a production environment might cause memory leaks as it omitted assertions & error handling.

[ansstuff]

Good news! Getter/setter for filterType has been added to MagicWand.
ImageMagick/ImageMagick@44dc2fb
Do you plan adding similar get/set methods to Wand?

[emcconville]

Do you plan adding similar get/set methods to Wand?

In time. Patience is important here. It'll take time for the work to be released as a stable version, it'll take time for bindings to update, and then it'll take time for bindings to release.

[ansstuff]

OK! Just wanted to make sure I don't need to do anything else for this to happen eventually.

[ansstuff]

I've tested 0.6.11 release, everything works as expected, thank you! This thread can be closed.