real image scaling algorithms?

[oldlaptop]

tkmprand currently scales images with Tk's built-in -zoom/-subsample features, which do dumb nearest-neighbor interpolation and dumb subsampling, respectively; in the unlikely event it ever has to upscale albumart, it'll look blocky and pixelated, and in the (virtually guaranteed) event it has to downscale it, it looks nasty and aliased. Options to fix this include:

• shell out to imagemagick's convert(1) if detected (present in almost any linux/unix system's package system)
• interface with TclMagick or some other C extension
• drag something like https://wiki.tcl-lang.org/page/Shrinking+an+image in (licensing unclear)
• write image-scaling code from scratch

For the moment I don't care about it enough to consider any of these worthwhile, except possibly a conditional shell-out to convert(1) since that'll be very quick (if dirty) and won't drag more dependency headaches in (building Img from scratch on !debian is bad enough).