Transforming the image with an arbitrary matrix

[vpenades]

Could it be possible to transform an image by an arbitrary matrix?

Something like this:

Matrix3x2 xform = Matrix3x2.CreateRotation(2) * Matrix3x2.CreateTranslation(5,0);
pl.AddTransform(new TransformMatrix(xform));

[saucecontrol]

Yep, that's entirely possible if you create your own IPixelTransform implementation.

I'm not clear what such a transform would do, though. Typically a 3x2 matrix transform is something you'd apply to vectors, not to pixels.

[vpenades]

The usual transformations applied to an image are scaling, rotation and translation, which happen to be a generalized as a matrix3x2.

So what this pixel transform would do is:

• loop over the destination pixels
• for every destination pixel, transform its pixel coordinates by the inverse of the input matrix
• copy the pixel from source, using the transformed pixel coordiantes

That would allow to have translation, rotation and scaling in a single pixel transformer

[saucecontrol]

It's not quite that simple, because a pixel value cannot be arbitrarily moved without distorting the image. In most cases, the transform will place the destination sample somewhere other than the center of a pixel, and in those cases, the destination pixel value must be interpolated by sampling several values from the source. This can be done, of course, but the general implementation is quite expensive in terms of memory bandwidth and computation (though well suited to GPU acceleration).

In general, I don't believe that kind of expensive transform fits with the philosophy of MagicScaler, so I'd not likely include it in-box. I do want people to be able to build those things or to be able to bridge into other libraries that provide them (e.g. SkiaSharp or ImageSharp) however, so if you attempt that and run into any issues, please let me know.