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Add joinChannel and toColourspace/toColorspace operations (#513)

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This commit is contained in:
Matt Hirsch
2016-08-17 10:42:05 -04:00
committed by Lovell Fuller
parent 72354d55a8
commit 5c5d74a903
17 changed files with 310 additions and 19 deletions
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docs/api.md
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@@ -60,7 +60,7 @@ Fast access to image metadata without decoding any compressed image data.
* `format`: Name of decoder used to decompress image data e.g. `jpeg`, `png`, `webp`, `gif`, `svg`
* `width`: Number of pixels wide
* `height`: Number of pixels high
* `space`: Name of colour space interpretation e.g. `srgb`, `rgb`, `scrgb`, `cmyk`, `lab`, `xyz`, `b-w` [...](https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/enumtypes.c#L522)
* `space`: Name of colour space interpretation e.g. `srgb`, `rgb`, `scrgb`, `cmyk`, `lab`, `xyz`, `b-w` [...](https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568)
* `channels`: Number of bands e.g. `3` for sRGB, `4` for CMYK
* `density`: Number of pixels per inch (DPI), if present
* `hasProfile`: Boolean indicating the presence of an embedded ICC profile
@@ -445,7 +445,7 @@ Convert to 8-bit greyscale; 256 shades of grey.
This is a linear operation. If the input image is in a non-linear colour space such as sRGB, use `gamma()` with `greyscale()` for the best results.
The output image will still be web-friendly sRGB and contain three (identical) channels.
By default the output image will be web-friendly sRGB and contain three (identical) color channels. This may be overridden by other sharp operations such as `toColourspace('b-w')`, which will produce an output image containing one color channel. An alpha channel may be present, and will be unchanged by the operation.
#### normalize() / normalise()
@@ -490,11 +490,17 @@ sharp('input.png')
});
```
#### toColourspace(colourspace) / toColorspace(colorspace)
Set the output colourspace. By default output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
`colourspace` is a string or `sharp.colourspace` enum that identifies an output colourspace. String arguments comprise vips colour space interpretation names e.g. `srgb`, `rgb`, `scrgb`, `cmyk`, `lab`, `xyz`, `b-w` [...](https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568)
#### extractChannel(channel)
Extract a single channel from a multi-channel image.
* `channel` is a zero-indexed integral Number representing the band number to extract. `red`, `green` or `blue` are also accepted as an alternative to `0`, `1` or `2` respectively.
`channel` is a zero-indexed integral Number representing the band number to extract. `red`, `green` or `blue` are also accepted as an alternative to `0`, `1` or `2` respectively.
```javascript
sharp(input)
@@ -505,6 +511,22 @@ sharp(input)
});
```
#### joinChannel(channels, [options])
Join a data channel to the image. The meaning of the added channels depends on the output colourspace, set with `toColourspace()`. By default the output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
`channels` is one of
* a single file path
* an array of file paths
* a single buffer
* an array of buffers
Note that channel ordering follows vips convention:
* sRGB: 0: Red, 1: Green, 2: Blue, 3: Alpha
* CMYK: 0: Magenta, 1: Cyan, 2: Yellow, 3: Black, 4: Alpha
Buffers may be any of the image formats supported by sharp: JPEG, PNG, WebP, GIF, SVG, TIFF or raw pixel image data. In the case of a RAW buffer, the `options` object should contain a `raw` attribute, which follows the format of the attribute of the same name in the `sharp()` constructor. See `sharp()` for details. See `raw()` for pixel ordering.
#### bandbool(operation)
Perform a bitwise boolean operation on all input image channels (bands) to produce a single channel output image.