node-pgm

This is a simple Reader/Writer for PGM (Portable Graymap) image files.

Usage

To use this module, import it into your code:

import { PGM, readPgmSync, writePgmSync } from 'node-pgm'

Creating a New PGM Instance

To create a new PGM, simply create a new instance of the PGM class. This creates a PGM with a width of 240px and a height of 360px, fills it with a gradient and saves it with the file name out.pgm.

import * as fs from 'fs'
import { PGM, writePgmSync } from 'node-pgm'

// create a PGM
const w = 240; const h = 360
const pgm = new PGM(w, h)

// fill with gradient
for (let y = 0; y < h; y++) {
  for (let x = 0; x < w; x++) {
    const c = Math.floor(x / w * y / h * 255)
    pgm.data.writeUInt8(c, y * w + x)
  }
}

// save
const buf = writePgmSync(pgm)
fs.writeFileSync('out.pgm', buf)

Reading and Writing PGM Files

To read a PGM file, use the readPgmSync function:

import * as fs from 'fs'
import { readPgmSync } from 'node-pgm'
const buffer = fs.readFileSync('myimage.pgm')
const pgm = readPgmSync(buffer)
console.log(pgm.width)
console.log(pgm.height)

To write a PGM file, use the writePgmSync function:

import * as fs from 'fs'
import { writePgmSync } from 'node-pgm'
const pgm = new PGM(100, 100)
const buffer = writePgmSync(pgm);
fs.writeFileSync('newimage.pgm', buffer);

Example

It reads src.pgm, inverts the colors and changes the descriptor and saves it to out.pgm.

import * as fs from 'fs'
import { readPgmSync, writePgmSync } from 'node-pgm'

// read
const file = fs.readFileSync('tests/files/gimp_binary.pgm')
const pgm = readPgmSync(file)
// invert the colors
for (let y = 0; y < pgm.height; y++) {
  for (let x = 0; x < pgm.width; x++) {
    const i = y * pgm.width + x
    const c = 255 - pgm.data.readUInt8(i)
    pgm.data.writeUInt8(c, i)
  }
}
// change descriptor from P5 to P2
pgm.descriptor = 'P2'

// save
const buf = writePgmSync(pgm)
fs.writeFileSync('out.pgm', buf)

API

PGM Class

Class for creating PGM.

Constructor

PGM(width, height)

Creates a new PGM instance with the specified width and height.

Properties

• width (number): The width of the image.
• height (number): The height of the image.
• comment (string): The comment associated with the image.
• descriptor (string): The descriptor of the PGM file. Default value is 'P5'.
• maxValue (number): The maximum pixel value. Default value is 255.
• data (Buffer): The pixel data of the image stored in a Buffer object.

Methods

trim(x, y, width, height)

Trims the image to the specified dimensions and position.

readPgmSync(buffer: Buffer): PGM

Take a PGM format buffer and return a PGM object.

writePgmSync(pgm: PGM): Buffer

Take a PGM object and return a PGM format buffer.

License

This module is available under the MIT License.