Support resize without preserving aspect ratio

[skedastik]

Goal

Add an ignoreAspectRatio method to support resizing of images to arbitrary aspect ratios, as requested in #118.

Behavior

Fixed width and height:

sharp('foo.jpg').ignoreAspectRatio().resize(300, 300);

Fixed width (leaving height unchanged):

sharp('foo.jpg').ignoreAspectRatio().resize(300);

Fixed height (leaving width unchanged):

sharp('foo.jpg').ignoreAspectRatio().resize(null, 300);

sharp's behavior is otherwise unchanged.

Code paths affected

• src/resize.cc
  • Canvas
    • Additional member IGNORE_ASPECT
  • ResizeWorker::Execute
    • Logic is mostly unchanged. Add separate x and y variables for factor, shrink, and residual.
    • Move small amount of logic into private class methods:
      • CalculateShrink
      • CalculateResidual
    • Use average of xresidual and yresidual to compute sigma for pre-affine-reduction Gaussian blur (see Progress on #118 (ignore aspect ratio) #191).
• index.js
  • New method Sharp.prototype.ignoreAspectRatio
    • Sets this.options.canvas to "ignore_aspect"
• test/unit/resize.js

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 1f4e1c1 on skedastik:judgement into 3810f64 on lovell:judgement.

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 1f4e1c1 on skedastik:judgement into 3810f64 on lovell:judgement.

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 1f4e1c1 on skedastik:judgement into 3810f64 on lovell:judgement.

[lovell]

Hi @jsongHBO @bkw @blowsie, as requestors of #118 are you able to help test @skedastik's great work on the feature you need?

[bkw]

Great work, @skedastik !
I noticed something odd with the size calculations, though:
Resizing a 610x600 image to 256x256 with ignoreAspectRatio() consistently results in a 256x260 image for me.

[skedastik]

Thanks, @bkw.
I'm having a hard time reproducing the bug on my end. Running vips-7.42.1 under OSX. I'm using a 610x600 input image with combinations of JPEG/PNG/TIFF inputs and outputs and getting a 256x256 result consistently. I'll keep you posted...

[bkw]

I just noticed I was a bit behind on my checkout of libvips. rebuilding with 7.42 now, will report back if it makes a difference.

[bkw]

I can still reproduce it with this:

var sharp = require('sharp'),
    request = require('request'),
    resizer = sharp().ignoreAspectRatio().resize(256,256);

request('http://i.imgur.com/dLKxTCk.jpg')
  .pipe(resizer)
  .pipe(sharp().metadata(console.log));

This gives the following output for me:

null { format: 'jpeg',
  width: 256,
  height: 260,
  space: 'srgb',
  channels: 3,
  hasProfile: false,
  hasAlpha: false }

Strange but true: Adding .gamma() produces the correct height of 256...

[skedastik]

Curiouser and curioser. Reproduced on my system. Looking into it...

[lovell]

Quick thought: possibly related to the use of gamma correction preventing JPEG shrink-on-load.

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 968736c on skedastik:judgement into 3810f64 on lovell:judgement.

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 968736c on skedastik:judgement into 3810f64 on lovell:judgement.

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling 968736c on skedastik:judgement into 3810f64 on lovell:judgement.

[skedastik]

Right again, @lovell. There was a typo in the JPEG shrink-on-load conditional. In fixing it I realized we could retain the shrink-on-load optimization even if the aspect ratio changes. An improvement all around!

Nice work exposing the bug @bkw.

Fix has been squashed and pushed.

[bkw]

I can confirm that for me it works as expected now. Thanks for the quick response, @skedastik !

[lovell]

Are you able to add a couple of tests for upscaling width but downscaling height and vice versa?

[coveralls]

Coverage increased (+0.03%) to 97.31% when pulling f72435c on skedastik:judgement into 3810f64 on lovell:judgement.

[skedastik]

More unit tests: done!

[lovell]

Fantastic, thank you Alaric. This will be included in the forthcoming v0.10.0 release.