gray

Work with 1 byte per pixel data

install

npm install @rgba-image/gray

usage

createGray

Creates an object similar to an ImageData, but the length of the .data property is width * height rather than width * height * 4

const { createGray } = require( '@rgba-image/gray' )

const width = 5
const height = 10
const gray = createGray( width, height )

const data = new Uint8ClampedArray( width, height )

data.fill( 127 )

const grayFromData = createGray( width, height, data )

extractChannel

Extract a single channel from the RGBA data

const { ALPHA_CHANNEL, extractChannel } = require( '@rgba-image/gray' )

// get some image here

const alpha = extractChannel( image, ALPHA_CHANNEL )

const x = 2
const y = 3
const width = 5
const height = 7

const alphaFromRegion = extractChannel( image, ALPHA_CHANNEL, x, y, width, height )

The channels are defined as numbers 0-3:

export const RED_CHANNEL = 0
export const GREEN_CHANNEL = 1
export const BLUE_CHANNEL = 2
export const ALPHA_CHANNEL = 3

There are aliases for extractChannel where you can omit the channel argument:

• extractRed
• extractGreen
• extractBlue
• extractAlpha

You can also get back an array of channels with extractRgba:

const { extractRgba } = require( '@rgba-image/gray' )

// get some image here

const [ red, green, blue, alpha ] = extractRgba( image )

maskImage

Mask the destination pixels using a GrayImage:

const { maskImage } = require( '@rgba-image/gray' )

// get an image in ImageData format and a mask in `GrayData` format here

maskImage( mask, image )


//mask a region:
const sourceX = 2
const sourceY = 3
const sourceWidth = 5
const sourceHeight = 7
const destX = 4
const destY = 6

maskImage( mask, image, sourceX, sourceY, sourceWith, sourceHeight, destX, destY )

fromAverage

Create a new GrayData image from an ImageData instance, the gray will be the average of the red, green and blue channels, ignoring alpha:

const { fromAverage } = require( '@rgba-image/gray' )

// get an image here

const averaged = fromAverage( image )

// from a region:
const x = 2
const y = 3
const width = 5
const height = 7

const averagedFromRegion = fromRegion( image, x, y, width, height )

fromLightness

Convert an image to grayscale.

Creates a new GrayData image from an ImageData instance, the gray will be the perceived lightness of the red, green and blue channels, ignoring alpha:

const { fromLightness } = require( '@rgba-image/gray' )

// get an image here

const grayscale = fromLightness( image )

// from a region:
const x = 2
const y = 3
const width = 5
const height = 7

const grayscaleFromRegion = fromLightness( image, x, y, width, height )

grayToImage

Create a normal ImageData instance from a GrayData instance

const { grayToImage } = require( '@rgba-image/gray' )

// get a gray image here

const image = grayToImage( gray )

// from a region
const x = 2
const y = 3
const width = 5
const height = 7

const imageFromRegion = grayToImage( gray, x, y, width, height )

// alpha is full opacity by default, you can specify it if you want:

const halfAlphaImage = grayToImage( gray, x, y, width, height, 127 )

combineChannels

Combines four GrayData instances of the same size to create a new ImageData:

const { combineChannels } = require( '@rgba-image/gray' )

// get your gray channels here

const image = combineChannels( red, green, blue, alpha )

By default, grayToImage and combineChannels use create-image

A factory function is exposed so that you can use a custom createImage, such as create-image-browser:

const createImage = require( '@rgba-image/create-image-browser' )
const { GrayToImageFactory } = require( '@rgba-image/gray' )

const { grayToImage, combineChannels } = GrayToImageFactory( createImage )

license

MIT License

Copyright (c) 2018 Nik Coughlin

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.