[CHICKEN]: http://call-cc.org
  [stb_image_resize.h]: https://github.com/nothings/stb

# stb-image-resize

This is a [CHICKEN] egg that wraps [stb_image_resize.h] version 0.95
from Jorge L Rodriguez and friends. It works on [CHICKEN] 4 and 5.

# API

    [procedure] (image-resize pixels width height channels target-width target-height #!key filter region alpha-channel)

Takes in raw `pixels` (a srfi-4 u8/u16/u32/f32vector) of size
`width`*`height`*`channels` and returns raw pixels after resizing. The
returned type is the same as `pixels`' of size
`target-width`*`target-height`*`channels`.

`channels` must be an integer between 0 and 64 and keys are processed
as follows.

- `filter:` one of `box`, `triangle`, `cubicbspline`, `catmullrom` or
  `mitchell`. The default uses `catmullrom` for up-sampling and
  `mitchell` for down-sampling.
- `region:` a vector of 4 elements `s0 t0 s1 t1`, representing the
  UV-coordinates to use as source image. This can be used to crop the
  image. These values must be in the range of `[0, 1]` and represent
  the fraction of the input image. `#(0 0 0.5 1)`, for example, cuts
  off the right half of the image.
- `alpha-channel:` index of channel which is the alpha channel in the
  image. supply `#f` (default) for no alpha channel.

# Examples

You can try `example-thumbnail.scm` like this:

![screenshot of running example-thumbnail.scm](example.png?raw=true)

Or turn a 3x1 greyscale image into a single pixel like this:

```
$ csi -R srfi-4 -R stb-image-resize -p '(image-resize (f32vector 0 4 8) 3 1 1   1 1)'
#f32(4.0)
```