image-blob-reduce

image-blob-reduce - downscale blobs with images inside
======================================================


> Wrapper for pica to work with blobs, with
> some sugar.

This is pica wrapper for convenient work with images from file input fields.
While pica works with raw bitmaps, this package operates with "image files".
Additional features are:

- \[jpeg] Apply orientation to downscaled result.
- \[jpeg] Keep metadata, but with patched orientation & removed original color
profile.
- Easy to monkey-patch for your needs.

Demo

Install
-------

``sh
npm install image-blob-reduce
`


Known issues
------------

This package is not compaible with some minification options. If you use
terser, disable evaluate or all compress options:

- { compress: { evaluate: false } }
- { compress: false }

This should not cause notable assets increase


Usage
-----

`js
const reduce = require('image-blob-reduce')();

//...

reduce
.toBlob(image_blob, { max: 1000 })
.then(blob => { ... });
`

If you load prebuild script in browser, use window.ImageBlobReduce


API
---

$3

Create new reducer. Options:

- pica - instance of pica, if you wish different defaults or shareable
webworkers pool.

Short call: require('image_blob_reduce')()

$3

Downscale image to fit into max\*max size. If blob contains jpeg, then
orientation is applied and metadata from original image reused (with minimal
change).

Options:

- __max__ - max allowed image size.
- __pica .resize() options__ - alpha, unsharpAmount, unsharpRadius,
unsharpThreshold, cancelToken

$3

The same as .toBlob(), but with canvas output.

$3

Inject your custom handler before specified method. See .init() source code
for example.

$3

The same as .before(), but handler is injected after specified method.

$3

Sugar to simplify assign of external plugins. Just calls
plugin_init(this, ...params).

$3

require('./lib/utils'), to simplify modifications.

$3

- ImageBlobReduce.pica => require('pica') - useful to customize pica options.

Customization

Since it's difficult to implement all possible options, this package is
specially designed for easy customization. See source code first.

- You can inherit class & replace existing methods.
- You can add extra actions before/after existing method.
- You can override existing methods of instance.

For example, if you wish force output to be always jpeg with some quality:

`js
const reducer = require('image-blob-reduce')();

reducer._create_blob = function (env) {
return this.pica.toBlob(env.out_canvas, 'image/jpeg', 0.8)
.then(function (blob) {
env.out_blob = blob;
return env;
});
};
`

Or rewrite scaling logic, introducing min option instead:

`js
const reducer = require('image-blob-reduce')();

reducer._calculate_size = function (env) {
const scale_factor = env.opts.min / Math.min(env.image.width, env.image.height);

if (scale_factor > 1) scale_factor = 1;

env.transform_width = Math.max(Math.round(env.image.width * scale_factor), 1);
env.transform_height = Math.max(Math.round(env.image.height * scale_factor), 1);

return env;
};
``