Feature Request: Filter Option for Resizing.

[mpelham]

Hey there! Great bit of work you've got here!

I'm currently using your plugin to downscale some PNGs for retina / non-retina support. Our artist took a great deal of care and time ensuring there was no aliasing of our PNGs for optimal compression, however, when downscaling, we run into a minor issue where Aliasing is applied.

Original:

Downscaled:

As there is no Filter Option as part of the grunt-image-resize task, there is no easy way to pass this into GraphicsMagick, however, it seems to be a fairly trivial task to add it.

On line 89 of image_resize.js:

var resizer = gm(filepath)
 .resize(imOptions.width, imOptions.height);

If I hack in:

var resizer = gm(filepath)
 .filter('Point')
 .resize(imOptions.width, imOptions.height);

I receive a Downscaled image with my specific use case solved for! Hooray!

Obviously, this is not the final solution for the code, I would propose we allow a new Option to be passed via Grunt, which is "filter" (Or "interpolation", I don't really care what we name it). Filter would default to what GraphicsMagick defaults to if not passed via Grunt.

Available options would include:
Point | Box | Triangle | Hermite | Hanning | Hamming | Blackman | Gaussian | Quadratic | Cubic | Catrom | Mitchell | Lanczos | Bessel | Sinc

From GraphicsMagick documentation, here: http://www.graphicsmagick.org/GraphicsMagick.html#details-filter

As most people want clean, smooth, aliased resizes which Grunt Image Resizes supports, this is definitely a unique use case, but it would be great to see it added!

[normanrz]

Hi @mpelham,
seems like you put quite some effort in this feature request already. Could you make a pull request out of it?

[nrshvch]

+1 I'm looking for a way to upscale 8bit graphics for my game, without AA.

[nrshvch]

Actually gm also has scale() method, which is same as filter("point").resize(), but faster.

[mpelham]

Hi @normanrz!

Sorry to be off the loop, this was actually a quick hackjob with some poor documentation (on my end) that worked perfectly for my use-case.

I'm glad that @dnarushevich jumped in to provide an alternate use case, and the GM method.
In my use-case, I run this rarely to optimize external_assets before dropping them onto S3 with a week cache at least, so "faster" isn't required.

I can't promise I'll get patches done anytime soon (I keep lazily dropping in the two lines I need when updates come out, sorry), but @dnarushevich / @normanrz, would you prefer something that allows unique resizer logic, and/or a series of options?

I would imagine you can pass either a function in the grunt command for the actual resize function, to satisfy Denis's use case, or options to filter resize.